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  • 1
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    Supply Response, Marginal Cost, and Soil Erosion Implications of Stover-based Biofuels (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-11
    Description: Existing economic analysis of corn stover as an energy feedstock has not considered potential changes in land use associated with different stover prices. We estimate the response of corn stover supply density to its price driven by changes in land use and examine its implications for a processing plant's pricing strategy and marginal cost, as well as associated changes in soil erosion. We find that plants will exploit the intensive margin as well as the extensive margin to secure additional amounts of stover. Our results show, counterintuitively, that a market for stover may result in lower soil erosion due to reallocations of land to continuous corn with removal, which, combined with no-till farming, results in lower soil erosion than the baseline without stover removal. Also contrary to expectations, using cover crops with stover removal may result in higher soil erosion due to land use changes within the fuel shed associated with optimal pricing.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q24 - Land, Q42 - Alternative Energy Sources
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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  • 2
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    On the response of the Earth to a fault system: its evaluation beyond the epicentral reference frame (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-24
    Description: Previous formalisms for determining the static perturbation of spherically symmetric self-gravitating elastic Earth models due to displacement dislocations deal with each infinitesimal element of the fault system in its epicentral reference frame. In this work, we overcome this restriction and present novel and compact formulas for obtaining the perturbation due to the whole fault system in an arbitrary and common reference frame. Furthermore, we show that, even in an arbitrary reference frame, it is still possible to discriminate the contributions associated with the polar, bipolar and quadrupolar patterns of the seismic source response, as well as their relation with the along strike, along dip and tensile components of the displacement dislocation. These results allow a better understanding of the relation between the static perturbation and the whole fault system, and find direct applications in geodetic problems, like the modelling of long-wavelength geoid or gravity data from GRACE and GOCE space missions and of the perturbation of the deviatoric inertia tensor of the Earth.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 3
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    A simple pendulum borehole tiltmeter based on a triaxial optical-fibre displacement sensor (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-26
    Description: Sensitive instruments like strainmeters and tiltmeters are necessary for measuring slowly varying low amplitude Earth deformations. Nonetheless, laser and fibre interferometers are particularly suitable for interrogating such instruments due to their extreme precision and accuracy. In this paper, a practical design of a simple pendulum borehole tiltmeter based on laser fibre interferometric displacement sensors is presented. A prototype instrument has been constructed using welded borosilicate with a pendulum length of 0.85 m resulting in a main resonance frequency of 0.6 Hz. By implementing three coplanar extrinsic fibre Fabry-Perot interferometric probes and appropriate signal filtering, our instrument provides tilt measurements that are insensitive to parasitic deformations caused by temperature and pressure variations. This prototype has been installed in an underground facility (Rustrel, France) where results show accurate measurements of Earth strains derived from Earth and ocean tides, local hydrologic effects, as well as local and remote earthquakes. The large dynamic range and the high sensitivity of this tiltmeter render it an invaluable tool for numerous geophysical applications such as transient fault motion, volcanic strain and reservoir monitoring.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 4
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    Constraints provided by ground gravity observations on geocentre motions (2016)
    Oxford University Press
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    Publication Date: 2016-07-08
    Description: The geocentre motion is the motion of the centre of mass of the entire Earth, considered an isolated system, in a terrestrial system of reference. We first derive a formula relating the harmonic degree-1 Lagrangian variation of the gravity at a station to both the harmonic degree-1 vertical displacement of the station and the displacement of the whole Earth's centre of mass. The relationship is independent of the nature of the Earth deformation and is valid for any source of deformation. We impose no constraint on the system of reference, except that its origin must initially coincide with the centre of mass of the spherically symmetric Earth model. Next, we consider the geocentre motion caused by surface loading. In a system of reference whose origin is the centre of mass of the solid Earth, we obtain a specific relationship between the gravity variation at the surface, the geocentre displacement and the load Love number $h^{\prime }_1$ , which demands the Earth's structure and rheological behaviour be known. For various networks of real or fictitious stations, we invert synthetic signals of surface gravity variations caused by atmospheric loading to retrieve the degree-1 variation of gravity. We then select six well-distributed stations of the Global Geodynamics Project, which is a world network of superconducting gravimeters, to invert actual gravity data for the degree-1 variations and determine the geocentre displacement between the end of 2004 and the beginning of 2012, assuming it to be due to surface loading. We find annual and semi-annual displacements with amplitude 0.5–2.3 mm.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 5
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    On computing the geoelastic response to a disk load (2016)
    Oxford University Press
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    Publication Date: 2016-05-05
    Description: We review the theory of the Earth's elastic and gravitational response to a surface disk load. The solutions for displacement of the surface and the geoid are developed using expansions of Legendre polynomials, their derivatives and the load Love numbers. We provide a matlab  function called diskload that computes the solutions for both uncompensated and compensated disk loads. In order to numerically implement the Legendre expansions, it is necessary to choose a harmonic degree, n max , at which to truncate the series used to construct the solutions. We present a rule of thumb (ROT) for choosing an appropriate value of n max , describe the consequences of truncating the expansions prematurely and provide a means to judiciously violate the ROT when that becomes a practical necessity.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 6
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    Constraints on seasonal load variations and regional rigidity from continuous GPS measurements in Iceland, 1997-2014 (2016)
    Oxford University Press
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    Publication Date: 2016-05-06
    Description: Two types of signals are clearly visible in continuous GPS (cGPS) time-series in Iceland, in particular in the vertical component. The first one is a yearly seasonal cycle, usually sinusoid-like with a minimum in the spring and a maximum in the fall. The second one is a trend of uplift, with higher values the closer the cGPS stations are to the centre of Iceland and ice caps. Here, we study the seasonal cycle signal by deriving its average at 71 GPS sites in Iceland. We estimate the annual and semi-annual components of the cycle in their horizontal and vertical components using a least-squares adjustment. The peak-to-peak amplitude of the cycle of the vertical component at the studied sites ranges from 4 mm near the coastline up to 27 mm at the centre of the Vatnajökull, the largest ice cap in Iceland. The minimum of the seasonal cycle occurs earlier in low lying areas than in the central part of Iceland, consistent with snow load having a large influence on seasonal deformation. Modelling shows that the seasonal cycle is well explained by accounting for elastically induced surface displacements due to snow, atmosphere, reservoir lake and ocean variations. Model displacement fields are derived considering surface loads on a multilayered isotropic spherical Earth. Through forward and inverse modelling, we were able to reproduce a priori information on the average seasonal cycle of known loads (atmosphere, snow in non-glaciated areas and lake reservoir) and get an estimation of other loads (glacier mass balance and ocean). The seasonal glacier mass balance cycle in glaciated areas and snow load in non-glaciated areas are the main contributions to the seasonal deformation. For these loads, induced seasonal vertical displacements range from a few millimetres far from the loads in Iceland, to more than 20 mm at their centres. Lake reservoir load also has to be taken into account on local scale as it can generate up to 20 mm of vertical deformation. Atmosphere load and ocean load are observable and generate vertical displacements in the order of a few millimetres. Inversion results also shows that the Iceland crust is less rigid than the world average. Interannual deviation from the GPS seasonal cycle can occur and are caused by unusual weather conditions over extended period of time.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 7
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    Optimization of regional constraints for estimating the Greenland mass balance with GRACE level-2 data (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-03
    Description: Data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission can be used to estimate the mass change rate for separate drainage systems (DSs) of the Greenland Ice Sheet (GrIS). One approach to do so is by inversion of the level-2 spherical harmonic data to surface mass changes in predefined regions, or mascons. However, the inversion can be numerically unstable for some individual DSs. This occurs mainly for DSs with a small mass change signal that are located in the interior region of Greenland. In this study, we present a modified mascon inversion approach with an improved implementation of the constraint equations to obtain better estimates for individual DSs. We use separate constraints for mass change variability in the coastal zone, where run-off takes place, and for the ice sheet interior above 2000 m, where mass changes are smaller. A multi-objective optimization approach is used to find optimal prior variances for these two areas based on a simulation model. Correlations between adjacent DSs are suppressed when our optimized prior variances are used, while the mass balance estimates for the combination of the DSs that make up the GrIS above 2000 m are not affected significantly. The resulting mass balance estimates for some DSs in the interior are significantly improved compared to an inversion with a single constraint, as determined by a comparison with mass balance estimates from surface mass balance modelling and discharge measurements. The rate of mass change of the GrIS for the period of January 2003 to December 2012 is found to be –266.1 ± 17.2 Gt yr –1 in the coastal zone and areas below 2000 m, and +8.2 ± 8.6 Gt yr –1 in the interior region.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 8
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    Integrated velocity field from ground and satellite geodetic techniques: application to Arenal volcano (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-17
    Description: Measurements of ground deformation can be used to identify and interpret geophysical processes occurring at volcanoes. Most studies rely on a single geodetic technique, or fit a geophysical model to the results of multiple geodetic techniques. Here we present a methodology that combines GPS, Total Station measurements and InSAR into a single reference frame to produce an integrated 3-D geodetic velocity surface without any prior geophysical assumptions. The methodology consists of five steps: design of the network, acquisition and processing of the data, spatial integration of the measurements, time series computation and finally the integration of spatial and temporal measurements. The most significant improvements of this method are (1) the reduction of the required field time, (2) the unambiguous detection of outliers, (3) an increased measurement accuracy and (4) the construction of a 3-D geodetic velocity field. We apply this methodology to ongoing motion on Arenal's western flank. Integration of multiple measurement techniques at Arenal volcano revealed a deformation field that is more complex than that described by individual geodetic techniques, yet remains consistent with previous studies. This approach can be applied to volcano monitoring worldwide and has the potential to be extended to incorporate other geodetic techniques and to study transient deformation.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 9
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    On the decorrelation filtering of RL05 GRACE data for global applications (2014)
    Oxford University Press
    Details
    Publication Date: 2014-11-09
    Description: In autumn 2012, the new release 05 (RL05) of monthly geopotencial spherical harmonics Stokes coefficients (SC) from Gravity Recovery and Climate Experiment (GRACE) mission was published. This release reduces the noise in high degree and order SC, but they still need to be filtered. One of the most common filtering processing is the combination of decorrelation and Gaussian filters. Both of them are parameters dependent and must be tuned by the users. Previous studies have analyzed the parameters choice for the RL05 GRACE data for oceanic applications, and for RL04 data for global application. This study updates the latter for RL05 data extending the statistics analysis. The choice of the parameters of the decorrelation filter has been optimized to: (1) balance the noise reduction and the geophysical signal attenuation produced by the filtering process; (2) minimize the differences between GRACE and model-based data and (3) maximize the ratio of variability between continents and oceans. The Gaussian filter has been optimized following the latter criteria. Besides, an anisotropic filter, the fan filter, has been analyzed as an alternative to the Gauss filter, producing better statistics.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 10
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    Transient gravity perturbations induced by earthquake rupture (2015)
    Oxford University Press
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    Publication Date: 2015-04-06
    Description: The static and transient deformations produced by earthquakes cause density perturbations which, in turn, generate immediate, long-range perturbations of the Earth's gravity field. Here, an analytical solution is derived for gravity perturbations produced by a point double-couple source in homogeneous, infinite, non-self-gravitating elastic media. The solution features transient gravity perturbations that occur at any distance from the source between the rupture onset time and the arrival time of seismic P waves, which are of potential interest for real-time earthquake source studies and early warning. An analytical solution for such prompt gravity perturbations is presented in compact form. We show that it approximates adequately the prompt gravity perturbations generated by strike-slip and dip-slip finite fault ruptures in a half-space obtained by numerical simulations based on the spectral element method. Based on the analytical solution, we estimate that the observability of prompt gravity perturbations within 10 s after rupture onset by current instruments is severely challenged by the background microseism noise but may be achieved by high-precision gravity strainmeters currently under development. Our analytical results facilitate parametric studies of the expected prompt gravity signals that could be recorded by gravity strainmeters.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 11
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    Transient gravity perturbations from a double-couple in a homogeneous half-space (2016)
    Oxford University Press
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    Publication Date: 2016-04-03
    Description: Seismic waves produced by fault ruptures give rise to gravity perturbations. So far, these perturbations have either been modelled as permanent coseismic gravity change in a half-space or spherical Earth model, or as full time-domain model in infinite space. In this paper, we present the explicit solution of gravity perturbations in time domain produced by a double-couple buried in a homogeneous half-space. This result is especially suited to study gravity perturbations up to a few hundreds of kilometres from the epicentre. It facilitates detailed parametric studies of gravity perturbations from fault rupture, and predicts gravity perturbations of real earthquakes with greatly improved accuracy. The results may serve to develop first designs of gravity-assisted earthquake early-warning systems, made possible by a new generation of ultrasensitive gravity gradiometers, which is currently under development.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 12
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    Five years gravity observation with the superconducting gravimeter OSG#058 at Syowa Station, East Antarctica: gravitational effects of accumulated snow mass (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-07
    Description: Continuous gravimetric observations have been made with three successive generations of superconducting gravimeter over 20 yr at Syowa Station ( $39.6\deg$ E, $69.0\deg$ S), East Antarctica. The third-generation instrument, OSG#058, was installed in January 2010 and was calibrated by an absolute gravimeter during January and February, 2010. The estimated scale factor was –73.823 ± 0.053 μGal V –1 (1 μGal = 10 –8 m s –2 ). The first 5 yr of OSG#058 data from 2010 January 7 to 2015 January 10 were decomposed into tidal waves (M3 to Ssa) and other non-tidal components by applying the Bayesian tidal analysis program BAYTAP. Long-term non-tidal gravity residuals, which were obtained by subtracting annual and 18.6 year tidal waves and the predicted gravity response to the Earth's variable rotation, showed significant correlation with the accumulated snow depth measured at Syowa Station. The greatest correlation occurred when the gravity variations lagged the accumulated snow depth by 21 d. To estimate the gravitational effect of the accumulated snow mass, we inferred a conversion factor of 3.13 ± 0.08 μGal m –1 from this relation. The accumulated snow depth at Syowa Station was found to represent an extensive terrestrial water storage (the snow accumulation) around Syowa Station, which was estimated from the Gravity Recovery and Climate Experiment satellite gravity data. The snow accumulation around Syowa Station was detectable by the superconducting gravimeter.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 13
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    AIUB-RL02: an improved time-series of monthly gravity fields from GRACE data (2016)
    Oxford University Press
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    Publication Date: 2016-04-07
    Description: The new release AIUB-RL02 of monthly gravity models from GRACE GPS and K-Band range-rate data is based on reprocessed satellite orbits referring to the reference frame IGb08. The release is consistent with the IERS2010 conventions. Improvements with respect to its predecessor AIUB-RL01 include the use of reprocessed (RL02) GRACE observations, new atmosphere and ocean dealiasing products (RL05), an upgraded ocean tide model (EOT11A), and the interpolation of shallow ocean tides (admittances). The stochastic parametrization of AIUB-RL02 was adapted to include daily accelerometer scale factors, which drastically reduces spurious signal at the 161 d period in C 20 and at other low degree and order gravity field coefficients. Moreover, the correlation between the noise in the monthly gravity models and solar activity is considerably reduced in the new release. The signal and the noise content of the new AIUB-RL02 monthly gravity fields are studied and calibrated errors are derived from their non-secular and non-seasonal variability. The short-period time-variable signal over the oceans, mostly representing noise, is reduced by 50 per cent with respect to AIUB-RL01. Compared to the official GFZ-RL05a and CSR-RL05 monthly models, the AIUB-RL02 stands out by its low noise at high degrees, a fact emerging from the estimation of seasonal variations for selected river basins and of mass trends in polar regions. Two versions of the monthly AIUB-RL02 gravity models, with spherical harmonics resolution of degree and order 60 and 90, respectively, are available for the time period from March 2003 to March 2014 at the International Center for Global Earth Models or from ftp://ftp.unibe.ch/aiub/GRAVITY/GRACE (last accessed 22 March 2016).
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 14
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    Is there a term structure in land lease rates? (2015)
    Oxford University Press
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    Publication Date: 2015-12-29
    Description: This article applies the concept of a term structure to agricultural land rental prices. Based on theoretical considerations, we develop a hedonic pricing model that allows for different shapes of the term structure curve while controlling for other price-relevant characteristics. We apply this model to land lease contracts in Saxony-Anhalt. We find an upward-sloping term structure during the agricultural price boom in 2007 and 2008, where market participants expected increasing rental prices. For the subsequent years, however, we detect a single-humped term structure. Hence, market participants revised their expectations and assumed a decline of land rental prices in the long term.
    Keywords: D44 - Auctions, E43 - Determination of Interest Rates ; Term Structure of Interest Rates, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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  • 15
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    Irrigation Decisions for Major West Coast Crops: Water Scarcity and Climatic Determinants (2015)
    Oxford University Press
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    Publication Date: 2015-12-13
    Description: This article uses the 2007 Farm and Ranch Irrigation Survey database developed by the U.S. Department of Agriculture to assess the impact of water scarcity and climate on irrigation decisions for producers of specialty crops, wheat, and forage crops. We estimate an irrigation management model for major crops in the West Coast (California, Oregon, and Washington), which includes a farm-level equation of irrigated share and crop-specific equations of technology adoption and water application rate (orchard/vineyard, vegetable, wheat, alfalfa, hay, and pasture). We find that economic and physical water scarcity, climate, and extreme weather, such as frost, extreme heat, and drought, significantly impact producers’ irrigation decisions. Producers use sprinkler technologies or additional water applications to mitigate risk of crop damage from extreme weather. Water application rates are least responsive to surface water cost or groundwater well depth for producers of orchard/vineyard. Water supply institutions influence producers’ irrigation decisions. Producers who receive water from federal agencies use higher water application rates and are less likely to adopt water-saving irrigation technologies for some crops. Institutional arrangements, including access to distinct water sources (surface or ground) and whether surface water cost is fee based, also affect the responsiveness of water application rates to changes in surface water cost. The analysis provides valuable information about how producers in irrigated agricultural production systems would respond and adapt to water pricing policies and climate change.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q16 - R&D ; Agricultural Technology ; Agricultural Extension Services, Q18 - Agricultural Policy ; Food Policy, Q54 - Climate ; Natural Disasters ; Global Warming
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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  • 16
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    Accounting for time- and space-varying changes in the gravity field to improve the network adjustment of relative-gravity data (2015)
    Oxford University Press
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    Publication Date: 2015-12-13
    Description: The relative gravimeter is the primary terrestrial instrument for measuring spatially and temporally varying gravitational fields. The background noise of the instrument—that is, non-linear drift and random tares—typically requires some form of least-squares network adjustment to integrate data collected during a campaign that may take several days to weeks. Here, we present an approach to remove the change in the observed relative-gravity differences caused by hydrologic or other transient processes during a single campaign, so that the adjusted gravity values can be referenced to a single epoch. The conceptual approach is an example of coupled hydrogeophysical inversion, by which a hydrologic model is used to inform and constrain the geophysical forward model. The hydrologic model simulates the spatial variation of the rate of change of gravity as either a linear function of distance from an infiltration source, or using a 3-D numerical groundwater model. The linear function can be included in and solved for as part of the network adjustment. Alternatively, the groundwater model is used to predict the change of gravity at each station through time, from which the accumulated gravity change is calculated and removed from the data prior to the network adjustment. Data from a field experiment conducted at an artificial-recharge facility are used to verify our approach. Maximum gravity change due to hydrology (observed using a superconducting gravimeter) during the relative-gravity field campaigns was up to 2.6 μGal d –1 , each campaign was between 4 and 6 d and one month elapsed between campaigns. The maximum absolute difference in the estimated gravity change between two campaigns, two months apart, using the standard network adjustment method and the new approach, was 5.5 μGal. The maximum gravity change between the same two campaigns was 148 μGal, and spatial variation in gravity change revealed zones of preferential infiltration and areas of relatively high groundwater storage. The accommodation for spatially varying gravity change would be most important for long-duration campaigns, campaigns with very rapid changes in gravity and (or) campaigns where especially precise observed relative-gravity differences are used in the network adjustment.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 17
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    Traveling ionospheric disturbances propagating ahead of the Tohoku-Oki tsunami: a case study (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-01
    Description: We document two kinds of traveling ionospheric disturbances, namely, CTIDs (Co-tsunami-Traveling-Ionospheric-disturbances) and ATIDs (Ahead-of-Tsunami-Traveling-Ionospheric-disturbances) related to the Tohoku-Oki tsunami of 2011 March 11. They are referred to the disturbances that remain behind and ahead of the principal tsunami wave front, respectively. We first note their presence in a numerical experiment performed using a simulation code coupling the tsunami, atmosphere and ionosphere. This code uses the tsunami wavefield as an input and simulates acoustic-gravity waves (AGWs) in the atmosphere and TIDs, in the form of total electron content (TEC) disturbance, in the ionosphere. The simulated TEC reveals the excitation of CTIDs (at about 2 TECU) and ATIDs (at about 1 TECU), representing up to 5 per cent disturbance over the ambient electron density, and they arise from the dissipation of AGWs in the thermosphere. A novel outcome is that during the tsunami passage between ~6° and 12° of epicentral distance, strong ATIDs arrive ~20–60 min ahead of the tsunami wave front covering ~3°–10° of distance from the tsunami location. Simulation results are compared with the far-field observations using GNSS satellites and confirm that ATIDs are the first detected TEC maximum, occurring 20–60 min ahead of the tsunami arrival. Our simulation also confirms the presence of largest TEC maximum representing CTIDs, 10–20 min after the first tsunami wave. ATIDs reported in this study have characteristics that can be potentially used for the early warning of the tsunami.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 18
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    Geological units and Moho depth determination in the Western Balkans exploiting GOCE data (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-20
    Description: In the present work we illustrate a new local inversion algorithm to retrieve the Moho depth from GOCE (Gravity field and steady-state Ocean Circulation Explorer) gravity field. In details the proposed procedure can be divided into two main steps: the first one consists in recognizing and isolating the different geological provinces in the study area by exploiting information coming from the GOCE global gravity field model. Once the main geological provinces are defined, a function relating the crust density of each province with depth is built and used to reduce the data. The gravitational effects of sediments, topography, bathymetry and upper mantle are also removed. In the second step the residual gravitational field is inverted to retrieve the Moho depth and some information on the crustal density. In particular, the clustering of geological province is performed by means of an automatic Bayesian classification algorithm while the inversion of GOCE residual field is performed by adapting the global algorithm developed in the framework of the GEMMA project to the local scale. The procedure, based on an iterative Wiener filter, allows to compute the Moho depth considering lateral as well as radial variations of crustal density. The algorithm has been applied to the fifth release of GOCE time-wise global gravity field model to infer information on the crustal structure in the Western Balkan area, that is, the region laying between Bulgaria and the Adriatic Sea. This region is one of the most complex and active, from the tectonic point of view, in the whole Europe and it is characterized by the presence of the Alpine-Himalayan orogenic belt, formed by the collision between the African and Eurasian plates, and by the opening of the Pannonian Basin. Results show a good agreement between the obtained geological provinces with the actual knowledge on the region. The resulting Moho depth ranges between about 20 km beneath the Adriatic Sea and 45 km in the Dinarides. Comparisons with available seismic data show differences smaller than 1 km (standard deviation).
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Decadal and quadratic variations of Earth's oblateness and polar ice mass balance from 1979 to 2010 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-29
    Description: Gravity variations associated with Earth's oblateness ( J 2 ) have been observed by satellite laser ranging (SLR) since 1976. The J 2 time-series has been used to measure and help understand many geophysical processes within the Earth system ranging from the mantle to the atmosphere. While post glacial rebound and the Earth climate system are believed to be the primary driving forces of long-term and seasonal J 2 variations, the physical cause of decadal and longer timescale J 2 variations has remained uncertain, although recent evidence indicates that polar ice mass changes are important. In this study, we estimate a variety of climate contributions to J 2 over the period 1979–2010, and find that ice mass variations in Greenland and Antarctica are the dominant cause of observed decadal and longer J 2 variations. Residual variations at periods near 10–11 years may reflect limitations of numerical climate models in estimating mass change variability at long periods, but are also suggestive of potential contribution related to variable solar activity.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Calibrating interferometric synthetic aperture radar (InSAR) images with regional GPS network atmosphere models (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-30
    Description: Interferometric synthetic aperture radar (InSAR) technology provides a valuable tool for obtaining Earth surface deformation and topography at high spatial resolution for crustal deformation studies. Similar to global positioning system (GPS), InSAR measurements are affected by the Earth's ionospheric and tropospheric layers as the electromagnetic signals significantly refract while propagating through the different layers. While GPS signals propagating through the neutral atmosphere are affected primarily by the distribution, pressure and temperature of atmospheric gases, including water vapour, the propagation through the ionosphere is mainly affected by the number of free electrons along the signal path. Here, we present the use of dense regional GPS networks for extracting tropospheric zenith delays and ionospheric total electron content (TEC) maps in order to reduce the noise levels in InSAR images. The results show significant reduction in the root mean square (RMS) values when simultaneously combining the two corrections, both at short time periods where no surface deformation is expected, and at longer periods, where imaging of localized subsidence and fault creep is enhanced.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Correction of inconsistencies in ECMWF's operational analysis data during de-aliasing of GRACE gravity models (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-30
    Description: The main objective of the Gravity Recovery and Climate Experiment (GRACE) Atmospheric and Oceanic De-Aliasing Level-1B product (AOD1B) is the removal of high-frequency non-tidal mass variations due to sub-monthly mass transport in the atmosphere and oceans. Application of AOD1B shall avoid aliasing of these high-frequency signals into monthly gravity models derived from modern gravity missions and shall help to derive consistent orbit solutions for altimetry and Satellite Laser Ranging missions. The AOD1B 6-h series of spherical harmonic coefficients up to degree and order 100 are routinely generated at the German Research Centre for Geoscience and distributed to the GRACE Science Data System and the user community. Inputs for this product are acquired from numerical weather prediction models which are regularly revised and consequently not stable in time. The latest AOD1B release 5 (RL05) is based, as all other releases, on input from ECMWF and does not resolve this problem of discontinuities present in the surface pressure and surface geopotential input data. This might contaminate the gravity field variations derived from atmospheric mass variations. In this paper we present a method to overcome this problem during future AOD1B product generation, as well as two new Level-2 products (GAE and GAF) that, over land, fix a posteriori the two jumps present in the already distributed Level-2 RL05 monthly gravity models which were based on AOD1B RL05. The impact of the proposed correction on the variations and long-term trend of the total mass of the atmosphere and on the ice mass balance over Antarctica and over Greenland is also illustrated. We found that the GAE/GAF-corrected trend of the global atmospheric mass over the GRACE mission lifetime significantly decreased from –0.05 to –0.02 mm yr –1 in terms of geoid height. A considerable effect (33 per cent) was also found in the quadratic term of ice mass loss over Antarctica which results in an acceleration of 3.2 Gt yr –1  yr –1 smaller than without applying this correction.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
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    Topics: Geosciences
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    The Economic Costs of Environmental Regulation in U.S. Dairy Farming: A Directional Distance Function Approach (2015)
    Oxford University Press
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    Publication Date: 2015-07-10
    Description: Analyses of the costs of regulating greenhouse gas emissions from dairy production, which could be used to assess the effectiveness of alternative policy measures, is a missing link in the literature. This article addresses this gap by establishing the economic impact associated with a hypothetical greenhouse gas environmental regulatory regime across major dairy producing counties in the United States. In doing so, the article makes three important contributions to the literature. First, it develops a comprehensive pollution index based on Environmental Protection Agency methodologies, which contrasts with previous studies that rely on partial measures based only on surplus nitrogen stemming from the over-application of fertilizer. Second, the article uses a directional output distance function, an approach that has not been employed previously to evaluate polluting technologies in the U.S. dairy sector. Third, the article incorporates a four-way error approach that accounts for unobserved county heterogeneity, time-invariant persistent technical efficiency, time-varying transient technical efficiency, and a random error. The results indicate that regulating greenhouse gas emissions from dairy farming would induce a 5-percentage point increase in average technical efficiency. In addition, the economic costs of implementing this hypothetical regulatory framework exhibit significant spatial variation across counties in the United States.
    Keywords: D22 - Firm Behavior: Empirical Analysis, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q52 - Pollution Control Costs ; Distributional Effects ; Employment Effects
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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    Did glacially induced TPW end the ice age? A reanalysis (2015)
    Oxford University Press
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    Publication Date: 2015-07-17
    Description: Previous studies of Earth rotation perturbations due to ice-age loading have predicted a slow secular drift of the rotation axis relative to the surface geography (i.e. true polar wander, TPW) of order of several degrees over the Plio-Pleistocene. It has been argued that this drift and the change in the geographic distribution of solar insolation that it implies may have been responsible for important transitions in ice-age climate, including the termination of ice-age cycles.We use a revised rotational stability theory that incorporates a more accurate treatment of the Earth's background ellipticity to reconsider this issue, and demonstrate that the net displacement of the pole predicted in earlier studies disappears. This more muted polar motion is due to two factors: first, the revised theory no longer predicts the permanent shift in the rotation axis, or the so-called ‘unidirectional TPW’, that appears in the traditional stability theory; and, second, the increased background ellipticity incorporated in the revised predictions acts to reduce the normal mode amplitudes governing the motion of the pole. We conclude that ice-age-induced TPW was not responsible for the termination of the ice age. This does not preclude the possibility that TPW induced by mantle convective flow may have played a role in major Plio-Pleistocene climate transitions, including the onset of Northern Hemisphere glaciation.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
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    Topics: Geosciences
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    Spurious barometric pressure acceleration in Antarctica and propagation into GRACE Antarctic mass change estimates (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-03
    Description: Apparent acceleration in Gravity Recovery and Climate Experiment (GRACE) Antarctic ice mass time-series may reflect both ice discharge and surface mass balance contributions. However, a recent study suggests there is also contamination from errors in atmospheric pressure de-aliasing fields [European Center for Medium-Range Weather Forecast (ECMWF) operational products] used during GRACE data processing. To further examine this question, we compare GRACE atmospheric pressure de-aliasing (GAA) fields with in situ surface pressure data from coastal and inland stations. Differences between the two are likely due to GAA errors, and provide a measure of error in GRACE solutions. Time-series of differences at individual weather stations are fit to four presumed error components: annual sinusoids, a linear trend, an acceleration term and jumps at times of known ECMWF model changes. Using data from inland stations, we estimate that atmospheric pressure error causes an acceleration error of about +7.0 Gt yr –2 , which is large relative to prior GRACE estimates of Antarctic ice mass acceleration in the range of –12 to –14 Gt yr –2 . We also estimate apparent acceleration rates from other barometric pressure (reanalysis) fields, including ERA-Interim, MERRA and NCEP/DOE. When integrated over East Antarctica, the four mass acceleration estimates (from GAA and the three reanalysis fields) vary considerably (by ~2–16 Gt yr –2 ). This shows the need for further effort to improve atmospheric mass estimates in this region of sparse in situ observations, in order to use GRACE observations to measure ice mass acceleration and related sea level change.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Importance of far-field topographic and isostatic corrections for regional density modelling (2016)
    Oxford University Press
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    Publication Date: 2016-08-27
    Description: The long-wavelength gravity field contains information about processes in the sublithospheric mantle. As satellite-derived gravity models now provide the long to medium-wavelength gravity field at unprecedented accuracy, techniques used to process gravity data need to be updated. We show that when determining these long-wavelengths, the treatment of topographic-isostatic effect (TIE) and isostatic effects (IE) is a likely source of error. We constructed a global isostatic model and calculated global TIE and IE. These calculations were done for ground stations as well as stations at satellite height. We considered both gravity and gravity gradients. Using these results, we determined how much of the gravity signal comes from distant sources. We find that a significant long-wavelength bias is introduced if far-field effects on the topographic effect are neglected. However, due to isostatic compensation far-field effects of the topographic effect are to a large degree compensated by the far-field IE. This means that far-field effects can be reduced effectively by always considering topographic masses together with their compensating isostatic masses. We show that to correctly represent the ultra-long wavelengths, a global background model should be used. This is demonstrated both globally and for a continental-scale case area in North America. In the case of regional modelling, where the ultra-long wavelengths are not of prime importance, gravity gradients can be used to help minimize correction errors caused by far-field effects.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Elastic tidal response of a laterally heterogeneous planet: a complete perturbation formulation (2016)
    Oxford University Press
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    Publication Date: 2016-08-12
    Description: Constraining laterally varying structures in planetary interiors is important for understanding both the composition and the internal dynamics of a planet. Recognizing that seismic imaging technique is currently only viable for studying the Earth's interior structures, methods that can be supported by advanced space geodetic techniques may become alternatives to ‘image’ the interiors of other planets. The method of tidal tomography is one possibility, and it relies on high precision measurement of the response of a planet to its body tide. However, it is essential to develop an efficient analytical tool that computes the dependence of tidal response to 3-D interior structures. In this paper, we present a complete formulation of such an analytical tool, which calculates to high accuracy the tidal response of a terrestrial planet with lateral heterogeneities in its elastic and density structures. We treat the lateral heterogeneities as small perturbations and derive the governing equations based on the perturbation theory. In a spherical harmonic representation, equations at each order of perturbation are reduced into multiple matrix equations at harmonics that are allowed by mode couplings, and the total response equals the sum of all those single-harmonic responses, which can be solved semi-analytically. We test our perturbation method by applying it to the Moon with a harmonic degree-1 mantle structure for which the perturbation solutions of the tidal response are compared with those from a fully numerical method. The remarkable agreement between results from these two methods validates the perturbation method. As an example, we then use the perturbation method to evaluate the impact of lunar crustal thickness variations on tidal response of the Moon. We find that lunar crust produces much smaller degree-3 tidal responses than a relatively weak degree-1 structure in the deep lunar mantle. Our calculations show that degree-3 tidal response measurements may hold key constraints on possible degree-1 mantle structure of the Moon, as suggested from previous modelling results.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
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    Topics: Geosciences
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    Generalized model for a Moho inversion from gravity and vertical gravity-gradient data (2016)
    Oxford University Press
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    Publication Date: 2016-08-14
    Description: Seismic data are primarily used in studies of the Earth's lithospheric structure including the Moho geometry. In regions, where seismic data are sparse or completely absent, gravimetric or combined gravimetric-seismic methods could be applied to determine the Moho depth. In this study, we derive and present generalized expressions for solving the Vening Meinesz–Moritz's (VMM) inverse problem of isostasy for a Moho depth determination from gravity and vertical gravity-gradient data. By solving the (non-linear) Fredholm's integral equation of the first kind, the linearized observation equations, which functionally relate the (given) gravity/gravity-gradient data to the (unknown) Moho depth, are derived in the spectral domain. The VMM gravimetric results are validated by using available seismic and gravimetric Moho models. Our results show that the VMM Moho solutions obtained by solving the VMM problem for gravity and gravity-gradient data are almost the same. This finding indicates that in global applications, using the global gravity/gravity-gradient data coverage, the spherical harmonic expressions for the gravimetric forward and inverse modelling yield (theoretically) the same results. Globally, these gravimetric solutions have also a relatively good agreement with the CRUST1.0 and GEMMA GOCE models in terms of their rms Moho differences (4.7 km and 4.1 km, respectively).
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
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    Topics: Geosciences
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    Drought Index Insurance for the Central Valley Project in California (2016)
    Oxford University Press
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    Publication Date: 2016-08-20
    Description: A multi-year drought has taken a severe toll on the agricultural economy of California’s Central Valley. Index insurance is an instrument with the potential to protect water users from economic losses due to periodic water shortages. An index insurance product based on the Sacramento Index and adapted to the Central Valley Project water supply is proposed. To address the potential for intertemporal adverse selection, three product designs are suggested: (1) "early bird" insurance; (2) variable premium insurance; and (3) variable deductible insurance. The performance of the designs are assessed using loss functions from the Westlands Water District in the San Joaquin Valley.
    Keywords: Q14 - Agricultural Finance, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q54 - Climate ; Natural Disasters ; Global Warming
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Investigating hydrological contributions to volcano monitoring signals: a time-lapse gravity example (2016)
    Oxford University Press
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    Publication Date: 2016-08-27
    Description: Geophysical techniques are widely used to monitor volcanic unrest. A number of studies have also demonstrated that hydrological processes can produce or trigger geophysical signals. Hydrologically induced gravity signals have previously been recorded by specifically designed gravity surveys as well as, inadvertently, by volcano monitoring studies. Water table corrections of microgravity surveys are commonplace. However, the fluctuations of the water table beneath survey locations are often poorly known, and such a correction fails to account for changes in water-mass storage in the unsaturated zone. Here, we combine 2-D axis-symmetrical numerical fluid-flow models with an axis-symmetric, distributed-mass, gravity calculation to model gravity changes in response to fluctuating hydrological recharge. Flow simulations are based on tropical volcanic settings where high surface permeabilities promote thick unsaturated zones. Our study highlights that mass storage (saturation) changes within the unsaturated zone beneath a survey point can generate recordable gravity changes. We show that for a tropical climate, recharge variations can generate gravity variations of over 150 μGal; although, we demonstrate that for the scenarios investigated here, the probability of recording such large signals is low. Our modelling results indicate that microgravity survey corrections based on water table elevation may result in errors of up to 100 μGal. The effect of inter-annual recharge fluctuations dominate over seasonal cycles which makes prediction and correction of the hydrological contribution more difficult. Spatial hydrogeological heterogeneity can also impact on the accuracy of relative gravity surveys, and can even result in the introduction of additional survey errors. The loading fluctuations associated with saturation variations in the unsaturated zone may also have implications for other geophysical monitoring techniques, such as geodetic monitoring of ground deformation.
    Keywords: Gravity, Geodesy and Tides
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    Topics: Geosciences
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    GRACE time-variable gravity field recovery using an improved energy balance approach (2015)
    Oxford University Press
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    Publication Date: 2015-10-25
    Description: A new approach based on energy conservation principle for satellite gravimetry mission has been developed and yields more accurate estimation of in situ geopotential difference observables using K-band ranging (KBR) measurements from the Gravity Recovery and Climate Experiment (GRACE) twin-satellite mission. This new approach preserves more gravity information sensed by KBR range-rate measurements and reduces orbit error as compared to previous energy balance methods. Results from analysis of 11 yr of GRACE data indicated that the resulting geopotential difference estimates agree well with predicted values from official Level 2 solutions: with much higher correlation at 0.9, as compared to 0.5–0.8 reported by previous published energy balance studies. We demonstrate that our approach produced a comparable time-variable gravity solution with the Level 2 solutions. The regional GRACE temporal gravity solutions over Greenland reveals that a substantially higher temporal resolution is achievable at 10-d sampling as compared to the official monthly solutions, but without the compromise of spatial resolution, nor the need to use regularization or post-processing.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
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    Topics: Geosciences
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    Monte Carlo simulation for background study of geophysical inspection with cosmic-ray muons (2016)
    Oxford University Press
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    Publication Date: 2016-06-19
    Description: Several attempts have been made to obtain a radiographic image inside volcanoes using cosmic-ray muons (muography). Muography is expected to resolve highly heterogeneous density profiles near the surface of volcanoes. However, several prior works have failed to make clear observations due to contamination by background noise. The background contamination leads to an overestimation of the muon flux and consequently a significant underestimation of the density in the target mountains. To investigate the origin of the background noise, we performed a Monte Carlo simulation. The main components of the background noise in muography are found to be low-energy protons, electrons and muons in case of detectors without particle identification and with energy thresholds below 1 GeV. This result was confirmed by comparisons with actual observations of nuclear emulsions. This result will be useful for detector design in future works, and in addition some previous works of muography should be reviewed from the view point of background contamination.
    Keywords: Gravity, Geodesy and Tides
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    Estimating the sea level highstand during the last interglacial: a probabilistic massive ensemble approach (2016)
    Oxford University Press
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    Publication Date: 2016-06-09
    Description: Essential to understanding sea level change and its causes during the last interglacial (LIG) is the quantification of uncertainties. In order to estimate the uncertainties, we develop a statistical framework for the comparison of palaeoclimatic sea level index points and GIA model predictions. For the investigation of uncertainties, as well as to generate better model predictions, we implement a massive ensemble approach by applying a data assimilation scheme based on particle filter methods. The different runs are distinguished through varying ice sheet reconstructions based on oxygen-isotope curves and different parameter selections within the GIA model. This framework has several advantages over earlier work, such as the ability to examine either the contribution of individual observations to the results or the probability of specific input parameters. This exploration of input parameters and data leads to a larger range of estimates than previously published work. We illustrate how the assumptions that enter into the statistical analysis, such as the existence of outliers in the observational database or the initial ice volume history, can introduce large variations to the estimate of the maximum highstand. Thus, caution is required to avoid overinterpreting results. We conclude that there are reasonable doubts whether the data sets previously used in statistical analyses are able to tightly constrain the value of maximum highstand during the LIG.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
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    An isostatic study of the Karoo basin and underlying lithosphere in 3-D (2016)
    Oxford University Press
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    Publication Date: 2016-06-01
    Description: A 3-D density model of the crust and upper mantle beneath the Karoo basin is presented here. The model is constrained using potential field, borehole and seismic data. Uplift of the basin by the end of the Cretaceous has resulted in an unusually high plateau (〉1000 m) covering a large portion of South Africa. Isostatic studies show the topography is largely compensated by changes in Moho depths (~35 km on-craton and 〉45 km off-craton) and changes in lithospheric mantle densities between the Kaapvaal Craton and surrounding regions (~50 kg m –3 increase from on- to off-craton). This density contrast is determined by inverted satellite gravity and gravity gradient data. The highest topography along the edge of the plateau (〉1200 m) and a strong Bouguer gravity low over Lesotho, however, can only be explained by a buoyant asthenosphere with a density decrease of around 40 kg m –3 .
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
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    Rotation change in the orientation of the centre-of-figure frame caused by large earthquakes (2016)
    Oxford University Press
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    Publication Date: 2016-06-19
    Description: A method to estimate the rotation change in the orientation of the centre-of-figure (CF) frame caused by earthquakes is proposed for the first time. This method involves using the point dislocation theory based on a spherical, non-rotating, perfectly elastic and isotropic (SNREI) Earth. The rotation change in the orientation is related solely to the toroidal displacements of degree one induced by the vertical dip slip dislocation, and the spheroidal displacements induced by an earthquake have no contribution. The effects of two recent large earthquakes, the 2004 Sumatra and the 2011 Tohoku-Oki, are studied. Results showed that the Sumatra and Tohoku-Oki earthquakes both caused the CF frame to rotate by at least tens of μas (micro-arc-second). Although the visible co-seismic displacements are identified and removed from the coordinate time-series, the rotation change due to the unidentified ones and errors in removal is non-negligible. Therefore, the rotation change in the orientation of the CF frame due to seismic deformation should be taken into account in the future in reference frame and geodesy applications.
    Keywords: Gravity, Geodesy and Tides
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    Topics: Geosciences
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    Formulation of geopotential difference determination using optical-atomic clocks onboard satellites and on ground based on Doppler cancellation system (2016)
    Oxford University Press
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    Publication Date: 2016-06-25
    Description: In this study, we propose an approach for determining the geopotential difference using high-frequency-stability microwave links between satellite and ground station based on Doppler cancellation system. Suppose a satellite and a ground station are equipped with precise optical-atomic clocks (OACs) and oscillators. The ground oscillator emits a signal with frequency f a towards the satellite and the satellite receiver (connected with the satellite oscillator) receives this signal with frequency f b which contains the gravitational frequency shift effect and other signals and noises. After receiving this signal, the satellite oscillator transmits and emits, respectively, two signals with frequencies f b and f c towards the ground station. Via Doppler cancellation technique, the geopotential difference between the satellite and the ground station can be determined based on gravitational frequency shift equation by a combination of these three frequencies. For arbitrary two stations on ground, based on similar procedures as described above, we may determine the geopotential difference between these two stations via a satellite. Our analysis shows that the accuracy can reach 1 m 2 s – 2 based on the clocks’ inaccuracy of about 10 –17 (s s –1 ) level. Since OACs with instability around 10 –18 in several hours and inaccuracy around 10 –18 level have been generated in laboratory, the proposed approach may have prospective applications in geoscience, and especially, based on this approach a unified world height system could be realized with one-centimetre level accuracy in the near future.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Who Really Benefits from Agricultural Subsidies? Evidence from Field-level Data (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-09
    Description: If agricultural subsidies are largely capitalized into farmland values through their effect on rental rates, then expanding support for agriculture may not benefit farmers who rent the land they farm. Existing evidence on the incidence of subsidies on cash rental rates is mixed. Identification is obscured by unobserved or imprecisely measured factors that tend to be correlated with subsidies, especially land quality and time-varying factors like commodity prices and adverse weather events. A problem that has received less attention is the fact that subsidies and land quality on rented land may differ from owned land. Since most farms possess both rented and owned acreage, farm-level measures of subsidies, land values, and rental rates may bias estimated incidence. Using a new, field-level data set that, for the first time, precisely links subsidies to land parcels, we show that this bias is considerable: where farm-level estimates suggest an incidence of 42–49 cents of the marginal subsidy dollar, field-level estimates from the same farms indicate that landlords capture just 20–28 cents. The size of the farm and the duration of the rental arrangement have substantial effects. Incidence falls by 5–15 cents when doubling total operated acres, and the incidence falls by 0.1–0.8 cents with each additional year of the rental arrangement. Low incidence of subsidies on rents combined with the farm-size and duration effects suggest that farmers renting land have monopsony power.
    Keywords: H22 - Incidence, Q14 - Agricultural Finance, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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    What Drives the Global "Land Rush"? (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-21
    Description: We review evidence regarding the size and evolution of the "land rush" in the wake of the 2007–8 boom in agricultural commodity prices, and we study the determinants of foreign land acquisition for large-scale agricultural investment. The use of data on bilateral investment relationships to estimate gravity models of transnational land-intensive investments confirms the central role of agro-ecological potential as a pull factor. However, this finding contrasts the standard literature insofar as the quality of the destination country's business climate is insignificant, and weak tenure security is associated with increased interest for investors to acquire land in the country. Policy implications are discussed.
    Keywords: F21 - International Investment ; Long-Term Capital Movements, O13 - Agriculture ; Natural Resources ; Energy ; Environment ; Other Primary Products, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q34 - Natural Resources and Domestic and International Conflicts
    Print ISSN: 0258-6770
    Electronic ISSN: 1564-698X
    Topics: Economics
    Published by Oxford University Press
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    Irrigated Agricultural Adaptation to Water and Climate Variability: The Economic Value of a Water Portfolio (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-18
    Description: Increasing aridity, more frequent and intense drought, and greater degrees of water scarcity create unique challenges for agriculture. In response to these challenges, which often manifest themselves as lower and more variable surface water supplies, as well as depleted and degraded ground water supplies, growers tend to seek opportunities to adapt. One option for growers to reduce their exposure to water scarcity and heightened uncertainty is to diversify. Indeed, access to a portfolio of supplies is one way in which water and irrigation districts, as well as individual growers, are responding to the changing landscape of water resource availability. This article evaluates the benefits to irrigated agriculture from having access to multiple sources of water. With farm-level information on 1,900 agricultural parcels across California, we use the hedonic property value method to investigate the extent that growers benefit from having access to multiple sources of water (i.e., a water portfolio). Our results suggest that while lower quality waters, less reliable water, and less water all negatively impact agricultural land values, holding a water portfolio has a positive impact on land values through its role in mitigating the negative aspects of these factors and reducing the sensitivity of agriculture to climate-related factors. From a policy perspective, such results identify a valuable adaptation tool that irrigation districts may consider to help offset the negative impacts of climate change, drought, and population increases on water supply availability and reliability.
    Keywords: Q10 - General, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy, Q50 - General, Q51 - Valuation of Environmental Effects
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Depth distribution of the sedimentary basin and Moho undulation in the Yellow Sea, NE Asia interpreted by using satellite-derived gravity field (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-24
    Description: We interpreted the TRIDENT satellite derived gravity field to provide detailed insights into the spatial distribution of the crustal density structures in the area of the Yellow Sea. We used 3-D forward density modelling for the interpretation that incorporated constraints from existing geological and geophysical information. A gravity stripping method is used to separate out the gravity effects of different geological crustal structures. From this analysis we see that (1) the Gunsan sedimentary basin is isostatically compensated. (2) The satellite-derived Bouguer anomalies ranging from 15 to –30 x 10 –5 m s –2 are linked to basin thicknesses in the Yellow Sea. (3) The calculated Moho depth in the Yellow Sea varies from 27 km beneath the deep sedimentary basin to 34 km in the uplifted zones. (4) Moho depth calculations show two distinct areas, characterized by the deepest Moho depths and the largest crustal thicknesses in the Yellow Sea. The one region extends along the Qianliyan Uplift Zone from Jiaodong to Hongsung while the other area extends from southeastern China to Hongsung in the Korean peninsula. Compared to previous works we suggest that they are the part of the collisions zone between North and South China Blocks extending from China to the Korean peninsula via the Yellow Sea.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    On the regularization of regional gravity field solutions in spherical radial base functions (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-19
    Description: Regional refinement of the gravity field models from satellite data using spherical radial base functions (SRBF) is an ill-posed problem. This is mainly due to the regional confinement of the data and the base functions, which leads to severe instabilities in the solutions. Here, this ill-posedness as well as the related regularization process are investigated. We compare three methods for the choice of the regularization parameter, which have been frequently used in gravity modelling. These methods are (1) the variance component estimation (VCE), (2) the generalized cross validation (GCV) and (3) the L-curve criterion. A particular emphasis is put on the impact of the SRBF type on the regularization parameter. To do this, we include two types of SRBF which are often used for regional gravity field modelling. These are the Shannon SRBF or the reproducing kernel and the Spline SRBF. The investigations are performed on two months of the real GOCE ultrasensitive gravity gradients over Central Africa and Amazon. The solutions are validated against a state-of-the-art global gravity solution. We conclude that if a proper regularization method is applied, both SRBF deliver more or less the same accuracy. We show that when the Shannon wavelet is used, the L-curve method gives the best results, while with the Spline kernel, the GCV outperforms the other two methods. Moreover, we observe that the estimated coefficients for the Spline kernel cannot be spatially interpreted. In contrast, the coefficients obtained for the Shannon wavelet reflect the energy of the recovered gravity field with a correlation factor of above 95 per cent. Therefore, when combined with the L-curve method, the Shannon SRBF is advantageous for regional gravity field estimation, since it is one of the simplest band-limited SRBF. In addition, it delivers promising solutions and the estimated coefficients represent the characteristics of the gravity field within the target region.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    A modified acceleration-based monthly gravity field solution from GRACE data (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-28
    Description: This paper describes an alternative acceleration approach for determining GRACE monthly gravity field models. The main differences compared to the traditional acceleration approach can be summarized as: (1) The position errors of GRACE orbits in the functional model are taken into account; (2) The range ambiguity is eliminated via the difference of the range measurements and (3) The mean acceleration equation is formed based on Cowell integration. Using this developed approach, a new time-series of GRACE monthly solution spanning the period January 2003 to December 2010, called Tongji_Acc RL01, has been derived. The annual signals from the Tongji_Acc RL01 time-series agree well with those from the GLDAS model. The performance of Tongji_Acc RL01 shows that this new model is comparable with the RL05 models released by CSR and JPL as well as with the RL05a model released by GFZ.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    A new bound constraints method for 3-D potential field data inversion using Lagrangian multipliers (2015)
    Oxford University Press
    Details
    Publication Date: 2015-02-19
    Description: In this paper, we present a method for incorporating prior geological information into potential field data inversion problem. As opposed to the traditional inverse algorithm, our proposed method takes full advantage of prior geological information as a constraint and thus obtains a new objective function for inversion by adding Lagrangian multipliers and slack variables to the traditional inversion method. These additional parameters can be easily solved during iterations. We used both synthetic and observed data sets to test the stability and validity of the proposed method. Our results using synthetic gravity data show that our new method predicts depth and density anomalies more efficiently and accurately than the traditional inversion method that does not include prior geological constraints. Then using observed gravity data in the Three Gorges area and geological constraint information, we obtained the density distribution of the upper and middle crust in this area thus revealing its geological structure. These results confirm the proposed method's validity and indicate its potential application for magnetism data inversion and exploration of geological structures.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Recurrent slow slip event reveals the interaction with seismic slow earthquakes and disruption from large earthquake (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-10
    Description: It remains enigmatic how slow slip events (SSEs) interact with other slow seismic events and large distant earthquakes at many subduction zones. Here we model the spatiotemporal slip evolution of the most recent long-term SSE in 2009–2011 in the Bungo Channel region, southwest Japan using GEONET GPS position time-series and a Kalman filter-based, time-dependent slip inversion method. We examine the space-time relationship between the geodetically determined slow slip transient and seismically observed low frequency earthquakes (LFEs) and very-low frequency earthquakes (V-LFEs) near the Nankai trough. We find a strong but distinct temporal correlation between transient slip and LFEs and V-LFEs, suggesting a different relationship to the SSE. We also find the great Tohoku-Oki earthquake appears to disrupt the normal source process of the SSE, probably reflecting large-scale stress redistribution caused by the earthquake. Comparison of the 2009–2011 SSE with others in the same region shows much similarity in slip and moment release, confirming its recurrent nature. Comparison of transient slip with plate coupling shows that slip transients mainly concentrate on the transition zone from strong coupling region to downdip LFEs with transient slip relieving elastic strain accumulation at transitional depth. The less consistent spatial correlation between the long-term SSE and seismic slow earthquakes, and susceptibility of these slow earthquakes to various triggering sources including long-term slow slip, suggests caution in using the seismically determined slow earthquakes as a proxy for slow slip.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    A normal mode treatment of semi-diurnal body tides on an aspherical, rotating and anelastic Earth (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-04
    Description: Normal mode treatments of the Earth's body tide response were developed in the 1980s to account for the effects of Earth rotation, ellipticity, anelasticity and resonant excitation within the diurnal band. Recent space-geodetic measurements of the Earth's crustal displacement in response to luni-solar tidal forcings have revealed geographical variations that are indicative of aspherical deep mantle structure, thus providing a novel data set for constraining deep mantle elastic and density structure. In light of this, we make use of advances in seismic free oscillation literature to develop a new, generalized normal mode theory for the tidal response within the semi-diurnal and long-period tidal band. Our theory involves a perturbation method that permits an efficient calculation of the impact of aspherical structure on the tidal response. In addition, we introduce a normal mode treatment of anelasticity that is distinct from both earlier work in body tides and the approach adopted in free oscillation seismology. We present several simple numerical applications of the new theory. First, we compute the tidal response of a spherically symmetric, non-rotating, elastic and isotropic Earth model and demonstrate that our predictions match those based on standard Love number theory. Second, we compute perturbations to this response associated with mantle anelasticity and demonstrate that the usual set of seismic modes adopted for this purpose must be augmented by a family of relaxation modes to accurately capture the full effect of anelasticity on the body tide response. Finally, we explore aspherical effects including rotation and we benchmark results from several illustrative case studies of aspherical Earth structure against independent finite-volume numerical calculations of the semi-diurnal body tide response. These tests confirm the accuracy of the normal mode methodology to at least the level of numerical error in the finite-volume predictions. They also demonstrate that full coupling of normal modes, rather than group coupling, is necessary for accurate predictions of the body tide response.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Decoupling of agricultural support payments: the impact on land market participation decisions (2012)
    Oxford University Press
    Details
    Publication Date: 2012-08-03
    Description: This paper analyses the impact of the recent decision by the European Union to ‘decouple’ agricultural support payments from agricultural production on Irish farmers' land market decisions. The land market participation decisions of Irish farmers are modelled using a dynamic probit model, while the extent of participation decisions is modelled using a dynamic tobit model. Decoupling does not appear to have significantly altered farmers' land market decisions. One likely explanation for this is the cross-compliance obligation for farmers to maintain land in a state fit for agricultural production in order to receive their full payments.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Fault locking near Istanbul: indication of earthquake potential from InSAR and GPS observations (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-26
    Description: A sequence of large earthquakes occurred along the North Anatolian fault in the 20th century. These earthquakes, including the 1999 Izmit/Düzce earthquakes, generally propagated westward towards the Marmara Sea, defining the Main Marmara fault as a potential seismic gap. It is important to conduct a detailed assessment of the seismic hazards along the main Marmara fault because the megacity Istanbul lies only approximately 10 km north of the eastern segment of the Main Marmara fault, which is referred to as the Princes’ Islands Fault segment (PIF). Here, we study the locking status of this fault segment to evaluate the seismic hazard potential. For the first time, combined ascending and descending Interferometric Synthetic Aperture Radar and Global Positioning System observations were used to investigate the crustal deformation associated with the PIF. After careful corrections of the estimated ground velocity, a deformation pattern relating to fault locking near the Princes’ Islands was identified. The modeling results revealed that the slip rate and locking depth of the fault segment show a clear trade-off, which were estimated as 18.9 ± 7.2 mm yr –1 and 12.1 ± 7.0 km, respectively. With a moment accumulation rate of 1.7 ± 0.4  x  10 17 Nm yr –1 (proportional to the product of slip rate and locking depth), our results imply a build-up of a geodetic moment on the PIF and therefore a potential for earthquake hazards in the vicinity of the Istanbul megacity.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    An improved geodetic source model for the 1999 Mw 6.3 Chamoli earthquake, India (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-20
    Description: We present a distributed slip model for the 1999 M w 6.3 Chamoli earthquake of north India using interferometric synthetic aperture radar (InSAR) data from both ascending and descending orbits and Bayesian estimation of confidence levels and trade-offs of the model geometry parameters. The results of fault-slip inversion in an elastic half-space show that the earthquake ruptured a $9 _{ - 2.2}^{\circ + 3.4}$ northeast-dipping plane with a maximum slip of ~1 m. The fault plane is located at a depth of ~ $15.9_{ - 3.0}^{ + 1.1}$ km and is ~120 km north of the Main Frontal Thrust, implying that the rupture plane was on the northernmost detachment near the mid-crustal ramp of the Main Himalayan Thrust. The InSAR-determined moment is 3.35 x 10 18 Nm with a shear modulus of 30 GPa, equivalent to M w 6.3, which is smaller than the seismic moment estimates of M w 6.4–6.6. Possible reasons for this discrepancy include the trade-off between moment and depth, uncertainties in seismic moment tensor components for shallow dip-slip earthquakes and the role of earth structure models in the inversions. The released seismic energy from recent earthquakes in the Garhwal region is far less than the accumulated strain energy since the 1803 M s 7.5 earthquake, implying substantial hazard of future great earthquakes.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    3-D linear inversion of gravity data: method and application to Basse-Terre volcanic island, Guadeloupe, Lesser Antilles (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-02
    Description: We use a Bayesian formalism combined with a grid node discretization for the linear inversion of gravimetric data in terms of 3-D density distribution. The forward modelling and the inversion method are derived from seismological inversion techniques in order to facilitate joint inversion or interpretation of density and seismic velocity models. The Bayesian formulation introduces covariance matrices on model parameters to regularize the ill-posed problem and reduce the non-uniqueness of the solution. This formalism favours smooth solutions and allows us to specify a spatial correlation length and to perform inversions at multiple scales. We also extract resolution parameters from the resolution matrix to discuss how well our density models are resolved. This method is applied to the inversion of data from the volcanic island of Basse-Terre in Guadeloupe, Lesser Antilles. A series of synthetic tests are performed to investigate advantages and limitations of the methodology in this context. This study results in the first 3-D density models of the island of Basse-Terre for which we identify: (i) a southward decrease of densities parallel to the migration of volcanic activity within the island, (ii) three dense anomalies beneath Petite Plaine Valley, Beaugendre Valley and the Grande-Découverte-Carmichaël-Soufrière Complex that may reflect the trace of former major volcanic feeding systems, (iii) shallow low-density anomalies in the southern part of Basse-Terre, especially around La Soufrière active volcano, Piton de Bouillante edifice and along the western coast, reflecting the presence of hydrothermal systems and fractured and altered rocks.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Estimation of the gravimetric pole tide by stacking long time-series of GGP superconducting gravimeters (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-20
    Description: We compute the gravimetric factor at the Chandler wobble (CW) frequency using time-series from superconducting gravimeters (SG) longer than a decade. We first individually process the polar motion and data at each individual gravity station to estimate the gravimetric factor amplitude and phase, then we make a global analysis by applying a stacking method to different subsets of up to seven SG stations. The stacking is an efficient way of getting rid of local effects and improving the signal-to-noise ratio of the combined data sets. Using the stacking method, we find a gravimetric factor amplitude and phase of 1.118 ± 0.016 and –0.45 ± 0.66 deg, respectively, which is smaller in amplitude than expected. The sources of error are then carefully considered. For both local and global analyses, the uncertainties on our results are reliably constrained by computing the standard deviation of the estimates of the gravimetric factor amplitude and phase for increasing length of the time-series. Constraints on the CW anelastic dissipation can be set since any departure of the gravimetric factor from its elastic value may provide some insights into the dissipative processes that occur at the CW period. In particular, assuming given rheological models for the Earth's mantle enables us to make the link between the gravimetric factor phase and the CW quality factor.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Temporal variation of tidal parameters in superconducting gravimeter time-series (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-21
    Description: Analysing independent 1-yr data sets of 10 European superconducting gravimeters (SG) reveals statistically significant temporal variations of M2 tidal parameters. Both common short-term (〈2 yr) and long-term (〉2 yr) features are identified in all SG time-series but one. The averaged variations of the amplitude factor are about 0.2. The path of load vector variations equivalent to the temporal changes of tidal parameters suggests the presence of an 8.85 yr modulation (lunar perigee). The tidal waves having the potential to modulate M2 with this period belong to the 3rd degree constituents. Their amplitude factors turn out to be much closer to body tide model predictions than that of the main 2nd degree M2, which indicates ocean loading for 3rd degree waves to be less prominent than for 2nd degree waves within the M2 group. These two different responses to the loading suggest that the observed modulation is more due to insufficient frequency resolution of limited time-series rather than to time variable loading. Presently, SG gravity time-series are still too short to prove if time variable loading processes are involved too as in case of the annual M2 modulation known to appear for analysis intervals of less than 1 yr. Whatever the variations are caused by, they provide the upper accuracy limit for earth model validation and permit estimating the temporal stability of SG scale factors and assessing the quality of gravity time-series.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Fault locking near Istanbul: indication of earthquake potential from InSAR and GPS observations (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-27
    Description: A sequence of large earthquakes occurred along the North Anatolian fault in the 20th century. These earthquakes, including the 1999 Izmit/Düzce earthquakes, generally propagated westward towards the Marmara Sea, defining the Main Marmara fault as a potential seismic gap. It is important to conduct a detailed assessment of the seismic hazards along the main Marmara fault because the megacity Istanbul lies only approximately 10 km north of the eastern segment of the Main Marmara fault, which is referred to as the Princes’ Islands Fault segment (PIF). Here, we study the locking status of this fault segment to evaluate the seismic hazard potential. For the first time, combined ascending and descending Interferometric Synthetic Aperture Radar and Global Positioning System observations were used to investigate the crustal deformation associated with the PIF. After careful corrections of the estimated ground velocity, a deformation pattern relating to fault locking near the Princes’ Islands was identified. The modeling results revealed that the slip rate and locking depth of the fault segment show a clear trade-off, which were estimated as 18.9 ± 7.2 mm yr –1 and 12.1 ± 7.0 km, respectively. With a moment accumulation rate of 1.7 ± 0.4  x  10 17 Nm yr –1 (proportional to the product of slip rate and locking depth), our results imply a build-up of a geodetic moment on the PIF and therefore a potential for earthquake hazards in the vicinity of the Istanbul megacity.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Coloured noise effects on deformation parameters of permanent GPS networks (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-06
    Description: Deformation analysis in general and strain analysis in particular using permanent GPS networks require proper analysis of time-series in which all functional effects are taken into consideration and all stochastic effects are captured using an appropriate noise model. This contribution addresses both issues when considering the strain parameters of a GPS network. Estimates of spatial correlation, time correlated noise, and multivariate power spectrum for daily position time-series of the Southern California Integrated GPS Network (SCIGN) stations collected between 1996 and 2011 are obtained. Significant signals with periods of 13.63 d and those related to the GPS draconitic year are identified in these time-series. We aim to assess the effect of a realistic noise model of the series on the uncertainties of the strain parameters including displacements, normal and shear strains, and rotations. For the SCIGN network considered, the following results are highlighted. Contrary to the common belief, the uncertainties of the displacements parameters become smaller when taking a realistic noise model into account. This however was not the case when assessing the noise characteristics of the normal and shear strain, and rotation parameters. The uncertainties increase nearly by a factor of two, in agreement to what is expected. Some of the significant deformation parameters of the white noise model become less significant in case of the realistic noise model.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Crustal vertical deformation response to different spatial scales of GRACE and GCMs surface loading (2015)
    Oxford University Press
    Details
    Publication Date: 2015-11-27
    Description: Crustal vertical deformation (CVD) observed by continuous GPS height time-series can be explained largely by surface loading effects recovered from both Gravity Recover and Climate Experiment (GRACE) and General Circulation Models (GCMs) data. We first show that lower degree CVD spatial spectrum due to the Earth's elastic response to a uniform surface loading plays more important roles than that of high-degree case. We then demonstrate that GRACE data with 300–400 km spatial resolution have the ability to detect 99 per cent power of global and regional CVD in spatial spectrum domain using a global frequency–wavenumber spectrum method. We can just use either GRACE or GCMs 36 degree/order (d/o) spherical harmonic coefficients (SHCs) which correspond to 500 km spatial resolution to acquire more than 90 per cent variance of total CVD modeled by up to 180 d/o SHCs at 98 per cent global gridpoints. Globally, CVD modeled by GRACE loading can explain 72 per cent annual amplitude and 69 per cent variance of GPS observed height time-series, which is better than the GCMs results of 64 per cent for annual amplitude and 41 per cent for variance. Using a three cornered hat method, we also show that the noise level of monthly averaged CVD is about 3 mm for both GPS height time-series and GRACE loading result, while that of GCMs result is only 1.3 mm.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Derivation of 3-D surface deformation from an integration of InSAR and GNSS measurements based on Akaike's Bayesian Information Criterion (2015)
    Oxford University Press
    Details
    Publication Date: 2015-11-25
    Description: We present a new method to derive 3-D surface deformation from an integration of interferometric synthetic aperture radar (InSAR) images and Global Navigation Satellite System (GNSS) observations based on Akaike's Bayesian Information Criterion (ABIC), considering relationship between deformations of neighbouring locations. This method avoids interpolated errors by excluding the interpolation of GNSS into the same spatial resolution as InSAR images and harnesses the data sets and the prior smooth constraints of surface deformation objectively and simultaneously by using ABIC, which were inherently unresolved in previous studies. In particular, we define surface roughness measuring smoothing degree to evaluate the performance of the prior constraints and deduce the formula of the covariance for the estimation errors to estimate the uncertainty of modelled solution. We validate this method using synthetic tests and the 2008 M w 7.9 Wenchuan earthquake. We find that the optimal weights associated with ABIC minimum are generally at trade-off locations that balance contributions from InSAR, GNSS data sets and the prior constraints. We use this method to evaluate the influence of the interpolated errors from the Ordinary Kriging algorithm on the derivation of surface deformation. Tests show that the interpolated errors may contribute to biasing very large weights imposed on Kriged GNSS data, suggesting that fixing the relative weights is required in this case. We also make a comparison with SISTEM method, indicating that our method allows obtaining better estimations even with sparse GNSS observations. In addition, this method can be generalized to provide a solution for situations where some types of data sets are lacking and can be exploited further to account for data sets such as the integration of displacements along radar lines and offsets along satellite tracks.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Impacts of GNSS position offsets on global frame stability (2015)
    Oxford University Press
    Details
    Publication Date: 2015-11-27
    Description: While it has been known for some time that offsets in the time-series of Global Navigation Satellite System (GNSS) position estimates degrade station velocity determinations, the magnitude of the effect has not been clear. Using products of the International GNSS Service (IGS), we assess the impact empirically by injecting progressively larger numbers of artificial offsets and solving for a series of long-term secular GNSS frames. Our results show that the stability of the IGS global frame datum is fairly robust, with significant effects at the formal error level only for the R x (and Y-pole) and R z rotational orientations. On the other hand, station velocity estimates are more seriously affected, especially the vertical component. For the typical IGS station, the mean vertical rate uncertainty is already limited to 0.34 mm yr –1 for the current set of position discontinuities. If the number of breaks doubles, which might occur using newer detection schemes, then that uncertainty will worsen by ~40 per cent to 0.48 mm yr –1 . This error source is generally a more important component of realistic velocity uncertainties than any other, including accounting for temporal correlations in the GNSS data. The only way to improve future GNSS velocity estimates is to severely limit manmade displacements at the tracking stations.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Responsiveness of Crop Yield and Acreage to Prices and Climate (2015)
    Oxford University Press
    Details
    Publication Date: 2015-12-13
    Description: We investigate the effect of crop price and climate variables on rainfed corn and soybean yields and acreage in the United States using a large panel dataset for the 1977–2007 period. Instrumental variables are used to control for endogeneity of prices in yield and acreage regressions, while allowing for spatially auto-correlated errors. We find that an increase in corn price has a statistically significant positive impact on corn yield, but the effect of soybean price on soybean yields is not statistically significant. The estimated price elasticities of corn yield and acreage are 0.23 and 0.45, respectively. Of the increase in corn supply caused by an increase in corn price, we find that 33.8% is due to price-induced yield enhancement and 66.2% is due to price-induced acreage expansion. We also find that the impact of climate change on corn production ranges from $-$ 7% to $-$ 41% and on soybean ranges from $-$ 8% to $-$ 45%, depending on the climate change scenarios, time horizon, and global climate models used to predict climate change. We show that the aggregate net impact of omitting price variables is an overestimation of the effect of climate change on corn yield by up to 9% and on soybean yield by up to 15%.
    Keywords: Q11 - Aggregate Supply and Demand Analysis ; Prices, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q54 - Climate ; Natural Disasters ; Global Warming
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Impact of Atmospheric and Oceanic De-aliasing Level-1B (AOD1B) products on precise orbits of altimetry satellites and altimetry results (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-03
    Description: We have extended backwards from 2001 to 1979 the current release 05 (RL05) of the Gravity Recovery and Climate Experiment (GRACE) Atmospheric and Oceanic De-aliasing Level-1B (AOD1B) product and studied the impact of this and a previous release 04 (RL04) of the AOD1B product on precise orbits of five altimetry satellites (ERS-1, ERS-2, TOPEX/Poseidon, Envisat and Jason-1) for the time span 1991–2012, as compared to the case when no AOD1B product is used. We have found that using AOD1B RL05 product reduces root mean square (RMS) fits of satellite laser ranging (SLR) observations by about 1.0–6.4 per cent, 2-d arc overlaps in radial, cross-track and along-track directions by about 1.3–12.0, 0.3–10.0 and 2.0–10.0 per cent, respectively, for various satellites tested, as compared to the case without AOD1B product. Using AOD1B RL05 product instead of RL04 one reduces SLR RMS fits by 0.1–0.7 per cent, 2-d arc overlaps in radial, cross-track and along-track directions by 0.1–0.6, 0.1–1.3 and 0.2–1.2 per cent, respectively, for the satellite orbits tested. The multi-mission crossover analysis shows that the application of an AOD1B product reduces the scatter of radial errors by 0.4–2.8 per cent for the satellite missions studied. At the regions with the most pronounced changes the use of the AOD1B products improves the consistency between the sea level as measured by the TOPEX and ERS-2 missions and by the Jason-1 and Envisat missions by 5 to 10 per cent (globally by about 2 per cent). The results of our study show that extended AOD1B RL05 product performs better than the AOD1B RL04 and improves orbits of altimetry satellites and consistency of sea level products.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Cooperation against theft: A test of incentives for water management In Tunisia (2014)
    Oxford University Press
    Details
    Publication Date: 2014-01-22
    Description: Water theft carried out by manipulating water meters constrains volumetric pricing in semi-arid regions. Cooperative management can reduce theft and improve incentives for efficient water use by inducing peer monitoring. Using a theoretical model, we show that theft is more likely when prices are high, punishments are weak, and cooperatives are large. We also show how cooperative membership and punishment levels are determined endogenously by constraints on monitoring. We test the model on data from Tunisia for the years 2001–2003, relying on instruments that proxy for unobservable monitoring costs. The results confirm that well-designed incentives can reduce theft, and that constraints on monitoring costs affect institutional design.
    Keywords: D82 - Asymmetric and Private Information, Q13 - Agricultural Markets and Marketing ; Cooperatives ; Agribusiness, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q25 - Water
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    A Natural Resource Theory of U.S. Crop Insurance Contract Choice (2014)
    Oxford University Press
    Details
    Publication Date: 2014-01-22
    Description: A large variety of subsidized crop insurance products are available to U.S. crop growers. Distinct and perhaps puzzling patterns in the choices of insurance products and coverage levels can be discerned. Where production conditions are better and yields are less risky then ( a ) higher insurance coverage levels are chosen; and ( b ) revenue insurance is preferred over yield insurance. Also, ( c ) the extent of preference for revenue insurance is stronger in more productive areas. Assuming, as many do, that growers seek to maximize subsidy transfers, point ( a ) can be explained by the interaction between yield technology and natural resource endowments. Points ( b ) and ( c ) can be explained by location in conjunction with the "natural hedge" and a contract design bias in how revenue insurance guarantees are computed. Empirical study of Risk Management Agency data on corn, soybean, and wheat yields, and insurance contract choices lend support to our model inferences.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy, Q24 - Land
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Capitalized Costs of Habitat Conservation Easements (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-05
    Description: Perpetual conservation easements permanently remove the option to convert existing habitat to more intensive agricultural production. If existing habitat is at threat of conversion, removing the option to convert will reduce land values. In this article, we estimate the land value discount resulting from perpetual habitat conservation easements by using propensity score matching. We find that on the average eased parcel, land values fall by approximately $86 per acre for every acre of eased habitat. On average, our results suggest that landowners have been adequately compensated and conservation agencies have successfully secured habitat at risk of conversion.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q24 - Land, Q57 - Ecological Economics: Ecosystem Services ; Biodiversity Conservation ; Bioeconomics
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Agri-environmental Policy and Urban Development Patterns: A General Equilibrium Analysis (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-05
    Description: This paper investigates the spatial effects that the provision of environmental public goods have on residential location choices in a suburban context. Specifically, a spatial general equilibrium framework is developed to analyze the consequences of adopting an agri-environmental policy promoting the provision of positive farming externalities. We use a static monocentric model of an open city where agricultural bid-rents and agricultural amenities vary endogenously in space, and where the positive externalities associated with agricultural production are valued by households. Consistent with empirical evidence of the potential side effects that conservation policies may have in terms of urbanization patterns and land price changes, we show that under certain conditions implementing an agri-environmental policy may promote additional suburban development. Moreover, we demonstrate that the emergence of disconnected suburban areas may be significantly influenced by the location of land regulated by an agri-environmental policy. Finally, we discuss distributional aspects and show that while introducing an agri-environmental policy has a negative impact on most residential land value, it can have positive effects on farmland and residential land located within the regulated areas, suggesting the non-neutrality of such policies regarding the agents’ assets.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy, R13 - General Equilibrium and Welfare Economic Analysis of Regional Economies, R14 - Land Use Patterns, R21 - Housing Demand
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Agricultural Rodent Control Using Barn Owls: Is It Profitable? (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-05
    Description: We develop a model to evaluate the profitability of controlling rodent damage by placing barn owl nesting boxes in agricultural areas. The model incorporates the spatial patterns of barn owl predation pressure on rodents, and the impact of this predation pressure on nesting choices and agricultural output. We apply the model to data collected in Israel and find the installation of nesting boxes profitable. While this finding indicates that economic policy instruments to enhance the adoption of this biological control method are redundant, it does support stricter regulations on rodent control using rodenticides.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy, Q57 - Ecological Economics: Ecosystem Services ; Biodiversity Conservation ; Bioeconomics
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    How do agricultural policies influence farm size inequality? The example of France (2011)
    Oxford University Press
    Details
    Publication Date: 2011-12-27
    Description: We investigate farm size inequality in France using agricultural censuses and farm structure surveys at the NUTS3 level (‘départements’) during the period 1970–2007. Using calculated Gini coefficients, we show that farm size inequality has not systematically increased in France. An econometric analysis of the determinants of farm size inequality reveals that policy measures significantly affected farm size inequality, with most of the measures considered decreasing it. Empirical results suggest that the main contributor was the activity of the SAFER (Société d'Aménagement Foncier et d'Etablissement Rural), a specific feature of the French farm structural policy aimed at regulating rural land management. Besides, this research highlights the great complexity of the dynamics underlying the evolution of farm size distribution.
    Keywords: D30 - General, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Optimisation of implementation policies of environmental quota trade (2011)
    Oxford University Press
    Details
    Publication Date: 2011-12-27
    Description: This paper analyses implementation policies of environmental quota trade, with the Flemish nutrient production rights as an example. Implementation policies concern the transaction quantity, quota reduction and prevention of speculation. They are analysed with a static and a dynamic multi-agent quota trade model. The static model with discrete non-auctioned quota trade shows that the obligation for quota sellers to entirely stop their production stimulates structural change. The dynamic model version indicates that a flat rate reduction on traded quota and measures taken to prevent speculation combined with too low penalties for overuse stimulate the total production.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Comment on: 'The quest for a consistent signal in ground and GRACE gravity time-series', by Michel Van Camp, Olivier de Viron, Laurent Metivier, Bruno Meurers and Olivier Francis (2014)
    Oxford University Press
    Details
    Publication Date: 2014-10-23
    Description: The paper in question by Van Camp and co-authors [MVC] challenges previous work showing that ground gravity data arising from hydrology can provide a consistent signal for the comparison with satellite gravity data. The data sets used are similar to those used previously, that is, the gravity field as measured by the GRACE satellites versus ground-based data from superconducting gravimeters (SGs) over the same continental area, in this case Central Europe. One of the main impediments in this paper is the presentation that is frequently confusing and misleading as to what the data analysis really shows, for example, the irregular treatment of annual components that are first subtracted then reappear in the analysis. More importantly, we disagree on specific points. Two calculations are included in our comment to illustrate where we believe that the processing in [MVC] paper is deficient. The first deals with their erroneous treatment of the global hydrology using a truncated spherical harmonic approach which explains almost a factor 2 error in their computation of the loading. The second shows the effect of making the wrong assumption in the GRACE/hydrology/surface gravity comparison by inverting the whole of the hydrology loading for underground stations. We also challenge their claims that empirical orthogonal function techniques cannot be done in the presence of periodic components, and that SG data cannot be corrected for comparisons with GRACE data. The main conclusion of their paper, that there is little coherence between ground gravity stations and this invalidates GRACE comparisons, is therefore questionable. There is nothing in [MVC] that contradicts any of the previous papers that have shown clearly a strong relation between seasonal signals obtained from both ground gravity and GRACE satellite data.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    The rotational feedback on linear-momentum balance in glacial isostatic adjustment (2014)
    Oxford University Press
    Details
    Publication Date: 2014-10-23
    Description: The influence of changes in surface ice-mass redistribution and associated viscoelastic response of the Earth, known as glacial isostatic adjustment (GIA), on the Earth's rotational dynamics has long been known. Equally important is the effect of the changes in the rotational dynamics on the viscoelastic deformation of the Earth. This signal, known as the rotational feedback, or more precisely, the rotational feedback on the sea level equation, has been mathematically described by the sea level equation extended for the term that is proportional to perturbation in the centrifugal potential and the second-degree tidal Love number. The perturbation in the centrifugal force due to changes in the Earth's rotational dynamics enters not only into the sea level equation, but also into the conservation law of linear momentum such that the internal viscoelastic force, the perturbation in the gravitational force and the perturbation in the centrifugal force are in balance. Adding the centrifugal-force perturbation to the linear-momentum balance creates an additional rotational feedback on the viscoelastic deformations of the Earth. We term this feedback mechanism, which is studied in this paper, as the rotational feedback on the linear-momentum balance. We extend both the time-domain method for modelling the GIA response of laterally heterogeneous earth models developed by Martinec and the traditional Laplace-domain method for modelling the GIA-induced rotational response to surface loading by considering the rotational feedback on linear-momentum balance. The correctness of the mathematical extensions of the methods is validated numerically by comparing the polar-motion response to the GIA process and the rotationally induced degree 2 and order 1 spherical harmonic component of the surface vertical displacement and gravity field. We present the difference between the case where the rotational feedback on linear-momentum balance is considered against that where it is not. Numerical simulations show that the resulting difference in radial displacement and sea level change between these situations since the Last Glacial Maximum reaches values of ±25 and ±1.8 m, respectively. Furthermore, the surface deformation pattern is modified by up to 10 per cent in areas of former or ongoing glaciation, but by up to 50 per cent at the bottom of the southern Indian ocean. This also results in the movement of coastlines during the last deglaciation to differ between the two cases due to the difference in the ocean loading, which is seen for instance in the area around Hudson Bay, Canada and along the Chinese, Australian or Argentinian coastlines.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Ocean contribution to seismic gravity changes: the sea level equation for seismic perturbations revisited (2014)
    Oxford University Press
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    Publication Date: 2014-09-20
    Description: During megathrust earthquakes, great ruptures are accompanied by large scale mass redistribution inside the solid Earth and by ocean mass redistribution due to bathymetry changes. These large scale mass displacements can be detected using the monthly gravity maps of the GRACE satellite mission. In recent years it has become increasingly common to use the long wavelength changes in the Earth's gravity field observed by GRACE to infer seismic source properties for large megathrust earthquakes. An important advantage of space gravimetry is that it is independent from the availability of land for its measurements. This is relevant for observation of megathrust earthquakes, which occur mostly offshore, such as the $M_{\text{w}} \sim 9$ 2004 Sumatra–Andaman, 2010 Maule (Chile) and 2011 Tohoku-Oki (Japan) events. In Broerse et al. , we examined the effect of the presence of an ocean above the rupture on long wavelength gravity changes and showed it to be of the first order. Here we revisit the implementation of an ocean layer through the sea level equation and compare the results with approximated methods that have been used in the literature. One of the simplifications usually lies in the assumption of a globally uniform ocean layer. We show that especially in the case of the 2010 Maule earthquake, due to the closeness of the South American continent, the uniform ocean assumption is not valid and causes errors up to 57 per cent for modelled peak geoid height changes (expressed at a spherical harmonic truncation degree of 40). In addition, we show that when a large amount of slip occurs close to the trench, horizontal motions of the ocean floor play a mayor role in the ocean contribution to gravity changes. Using a slip model of the 2011 Tohoku-Oki earthquake that places the majority of slip close to the surface, the peak value in geoid height change increases by 50 per cent due to horizontal ocean floor motion. Furthermore, we test the influence of the maximum spherical harmonic degree at which the sea level equation is performed for sea level changes occurring along coastlines, which shows to be important for relative sea level changes occurring along the shore. Finally, we demonstrate that ocean floor loading, self-gravitation of water and conservation of water mass are of second order importance for coseismic gravity changes. When GRACE observations are used to determine earthquake parameters such as seismic moment or source depth, the uniform ocean layer method introduces large biases, depending on the location of the rupture with respect to the continent. The same holds for interpreting shallow slip when horizontal motions are not properly accounted for in the ocean contribution. In both cases the depth at which slip occurs will be underestimated.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Intensive and extensive margin adjustments to water scarcity in France's Cereal Belt (2014)
    Oxford University Press
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    Publication Date: 2014-11-11
    Description: Efficient water management in agriculture is becoming critical due to increasing environmental constraints and global food and bio-energy demands. Farmers may respond to increased water scarcity along three main adjustment margins: a move towards rain-fed agriculture (super-extensive margin) or towards less water-intensive crops (extensive margin), and a reduction in water intensity for irrigated crops (intensive margin). Using a positive mathematical programming model of regional supply calibrated to economic and agronomic information, we decompose the total effect of reduced water availability on these adjustment margins in Beauce, a productive cereal region that relies on a groundwater resource to meet its irrigation needs. For realistic water scarcity scenarios, 57 per cent of the total response is attributable to super-extensive margin adjustments. The extensive margin represents 28 per cent of the total response, while the intensive margin accounts for 15 per cent. Crop-level analysis reveals more subtle adaptation patterns.
    Keywords: Q11 - Aggregate Supply and Demand Analysis ; Prices, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q25 - Water
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Encouraging Reductions in Nonpoint Source Pollution through Point-nonpoint Trading: The Roles of Baseline Choice and Practice Subsidies (2014)
    Oxford University Press
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    Publication Date: 2014-09-06
    Description: Water quality regulations in the United States apply almost exclusively to point sources. In impaired watersheds where both point and nonpoint sources contribute to pollution, the U.S. Environmental Protection Agency (EPA) is encouraging the use of point-nonpoint trading to reduce the cost of point sources to meet their permit requirement, and to encourage nonpoint sources to voluntarily contribute more towards meeting overall water quality goals. The EPA guidance encourages trading programs to set a nonpoint source eligibility baseline that extracts some "extra" abatement from nonpoint sources. Research has shown that setting an eligibility baseline that is substantially more stringent than current management could discourage nonpoint source participation and significantly hinder trading. In this paper we examine how choosing the eligibility baseline for agricultural sources affects the efficiency goal of trading (reducing costs to point sources), as well as how it affects the EPA goal of encouraging nonpoint abatement. Using data from the Chesapeake Bay Watershed we find that eligibility baselines set to encourage additional nonpoint source abatement reduce the supply of credits in a market; the more stringent the baseline, the fewer the trades and the smaller the overall abatement from nonpoint sources. A subsidy to farmers for reducing the cost of meeting a baseline encourages greater nonpoint source abatement, but may not benefit the trading market.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q20 - General, Q58 - Government Policy
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Investigating long-term subsidence at Medicine Lake Volcano, CA, using multitemporal InSAR (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-07
    Description: Long-term volcanic subsidence provides insight into intereruptive processes, which comprise the longest portion of the eruptive cycle. Ground-based geodetic surveys of Medicine Lake Volcano (MLV), northern CA, document subsidence at rates of ~–10 mm yr –1 between 1954 and 2004. The long observation period plus the duration and stable magnitude of this signal presents an ideal opportunity to study long-term volcanic deformation, but this first requires accurate knowledge of the geometry and magnitude of the source. Best-fitting analytical source models to past levelling and GPS data sets show conflicting source parameters—primarily the model depth. To overcome this, we combine multiple tracks of InSAR data, each with a different look angle, to improve upon the spatial resolution of ground-based measurements. We compare the results from InSAR to those of past geodetic studies, extending the geodetic record to 2011 and demonstrating that subsidence at MLV continues at ~–10 mm yr –1 . Using geophysical inversions, we obtain the best-fitting analytical source model—a sill located at 9–10 km depth beneath the caldera. This model geometry is similar to those of past studies, providing a good fit to the high spatial density of InSAR measurements, while accounting for the high ratio of vertical to horizontal deformation derived from InSAR and recorded by existing levelling and GPS data sets. We discuss possible causes of subsidence and show that this model supports the hypothesis that deformation at MLV is driven by tectonic extension, gravitational loading, plus a component of volume loss at depth, most likely due to cooling and crystallization within the intrusive complex that underlies the edifice. Past InSAR surveys at MLV, and throughout the Cascades, are of variable success due to dense vegetation, snow cover and atmospheric artefacts. In this study, we demonstrate how InSAR may be successfully used in this setting by applying a suite of multitemporal analysis methods that account for atmospheric and orbital noise sources. These methods include: a stacking strategy based upon the noise characteristics of each data set; pixelwise rate-map formation (-RATE) and persistent scatterer InSAR (StaMPS).
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    The coseismic slip distribution of a shallow subduction fault constrained by prior information: the example of 2011 Tohoku (Mw 9.0) megathrust earthquake (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-11
    Description: In the literature, the inverted coseismic slip models from seismological and geodetic data for the 2011 Tohoku-Oki earthquake portray significant discrepancies, in particular regarding the intensity and the distribution of the rupture near the trench. For a megathrust earthquake, it is difficult to discern the slip along the shallow part of the fault from the geodetic data, which are often acquired on land. In this paper, we discuss the uncertainties in the slip distribution inversion using the geodetic data for the 2011 Tohoku earthquake and the Fully Bayesian Inversion method. These uncertainties are due to the prior information regarding the boundary conditions at the edges of the fault, the dip subduction angle and the smoothing operator. Using continuous GPS data from the Japan Island, the results for the rigid and free boundary conditions show that they produce remarkably different slip distributions at shallow depths, with the latter producing a large slip exceeding 30 m near the surface. These results indicate that the smoothing operator (gradient or Laplacian schemes) does not severely affect the slip pattern. To better invert the coseismic slip, we then introduce the ocean bottom GPS (OB-GPS) data, which improve the resolution of the shallow part of the fault. We obtain a near-trench slip greater than 40 m that reaches the Earth's surface, regardless of which boundary condition is used. Additionally, we show that using a mean dip angle for the fault as derived from subduction models is adequate if the goal is to invert for the general features of the slip pattern of this megathrust event.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Individual and Cooperative Management of Invasive Species in Human-mediated Landscapes (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-13
    Description: As a bioinvasion spreads across a landscape from its point of introduction, damages rise roughly with the square of the distance from the original invasion. It is thus generally beneficial, at the landscape scale, to apply eradication or containment controls early if not immediately upon discovery. However, an individual property owner only has incentives to consider the costs and benefits of control on his/her own property rather than potential landscape-scale damages. Bioinvasions will therefore generally be under-controlled in a landscape of independent owners operating under a laissez-faire system. A mechanism is thus needed to induce early cooperative contributions to control costs from beneficiaries who would, without them, be invaded later. We develop a spatially-explicit, integrated model of invasion spread and human behavior to examine how different degrees of spatial cooperation affect patterns of invasion spread and the total costs and damages imposed. We compare individual laissez-faire, cooperative control by adjacent neighbors, and cooperative control by groups including more distant but nearby neighbors. As expected, private laissez-faire control decisions tend to under-control the invasion relative to socially optimal control under most circumstances. But a reasonably high fraction of first best payoffs can be achieved with only a modest geographical reach of cooperation. We also find that less extensive cooperation is needed to control invasions whose costs and damages otherwise lead to the largest externalities (circumstances with costs that are relatively low compared with damages). This suggests that even small amounts of cooperation to control bioinvasions can provide large social benefits.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q24 - Land, Q57 - Ecological Economics: Ecosystem Services ; Biodiversity Conservation ; Bioeconomics
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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    Farmland Protection and Agricultural Land Values at the Urban-Rural Fringe: British Columbia's Agricultural Land Reserve (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-13
    Description: Farmland conservation policies typically use zoning and differentiated taxes to prevent urban development of farmland, but little is known about the effectiveness of these policies. This study adds to current knowledge by examining the impact of British Columbia's Agricultural Land Reserve (ALR), established in 1973, which severely restricts subdivision and nonagricultural uses for more than 4.7 million hectares of farmland. To determine the extent to which the ALR preserves farmland by reducing or removing the development option, a multilevel hedonic pricing model is used to estimate the impact of land use, geographic, and zoning characteristics on farmland value near the capital city of Victoria on Vancouver Island. Using sales data from 1974 through 2008, the model demonstrates a changing ALR impact over time that varies considerably by improved and unimproved land types. In 2008, landowners paid 19% less for the typical improved farmland parcel within the ALR versus that outside it. This suggests that would-be developers expect permanency in the zoning law, and prefer non-ALR zoned land. However, ALR land that is unimproved has a premium of 55%, suggesting that this land is more valuable for agriculture than for development. Farmland located closer to the city or the commuting highway commands a premium if it has a residence on it, with a residence also explaining why smaller agricultural properties sell at higher prices. However, it appears that zoning by itself is insufficient to protect farmland; other policies likely need to be implemented in conjunction with zoning to protect agricultural land.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q28 - Government Policy, R14 - Land Use Patterns
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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    Capitalized Amenity Value of Native Vegetation in a Multifunctional Rural Landscape (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-13
    Description: In many parts of the world, natural vegetation has been cleared to allow agricultural production. To ensure a long-term flow of ecosystem services without compromising agricultural activities, restoring the environment requires a balance between public and private benefits and costs. Information about private benefits generated by environmental assets can be utilized to identify conservation opportunities on private lands, evaluate environmental projects, and design effective policy instruments. We use a spatio-temporal hedonic model to estimate the private benefits of native vegetation on rural properties in the state of Victoria, Australia. Specifically, we estimate the marginal value of native vegetation on private land and examine how it varies with the extent of vegetation on a property and across a range of property types and sizes. Private benefits of native vegetation are greater per unit area on small and medium-sized properties and smaller on large production-oriented farms. Native vegetation exhibits diminishing marginal benefits as its proportion of a property increases. The current extent of native vegetation cover is lower than the extent that would maximize the amenity value to many landowners. There is scope for improved targeting of investment in the study region by incorporating private benefits of environmental projects into environmental planning processes. Landowners with high marginal private benefits from revegetation would be more willing to participate in a revegetation program. Targeting these landowners would likely provide higher value for money because such projects could be implemented at lower public cost.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q57 - Ecological Economics: Ecosystem Services ; Biodiversity Conservation ; Bioeconomics
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Desmoothing of averaged periodical signals for geodetic applications (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-01
    Description: In general, observations are normally considered to refer to an epoch in time, however, observations take time. During this time span temporal variations of the observable alias the measurement. Similar phenomenon can be defined in the space domain as well: data treated to refer to a geographical location often contains integrated information of the surroundings. In each case the appropriate signal content can partially be recovered by desmoothing the averaged data. The present study delivers the theoretical foundation of a desmoothing method, and suggests its use on different applications in geodesy. The theoretical formulation of the desmoothing has been derived for 1-D and 2-D signals, the latter is interpreted on a plain and also on a sphere. The presented case studies are less elaborated, but intended to demonstrate the need and usefulness of the desmoothing tool.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Estimation of offsets in GPS time-series and application to the detection of earthquake deformation in the far-field (2015)
    Oxford University Press
    Details
    Publication Date: 2015-01-08
    Description: Extracting geophysical signals from Global Positioning System (GPS) coordinate time-series is a well-established practice that has led to great insights into how the Earth deforms. Often small discontinuities are found in such time-series and are traceable to either broad-scale deformation (i.e. earthquakes) or discontinuities due to equipment changes and/or failures. Estimating these offsets accurately enables the identification of coseismic deformation estimates in the former case, and the removal of unwanted signals in the latter case which then allows tectonic rates to be estimated more accurately. We develop a method to estimate accurately discontinuities in time series of GPS positions at specified epochs, based on a so-called ‘offset series’. The offset series are obtained by varying the amount of GPS data before and after an event while estimating the offset. Two methods, a mean and a weighted mean method, are then investigated to produce the estimated discontinuity from the offset series. The mean method estimates coseismic offsets without making assumptions about geophysical processes that may be present in the data (i.e. tectonic rate, seasonal variations), whereas the weighted mean method includes estimating coseismic offsets with a model of these processes. We investigate which approach is the most appropriate given certain lengths of available data and noise within the time-series themselves. For the Sumatra–Andaman event, with 4.5 yr of pre-event data, we show that between 2 and 3 yr of post-event data are required to produce accurate offset estimates with the weighted mean method. With less data, the mean method should be used, but the uncertainties of the estimated discontinuity are larger.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Detection of gravity field source boundaries using deconvolution method (2014)
    Oxford University Press
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    Publication Date: 2014-10-16
    Description: Complications arise in the interpretation of gravity fields because of interference from systematic degradations, such as boundary blurring and distortion. The major sources of these degradations are the various systematic errors that inevitably occur during gravity field data acquisition, discretization and geophysical forward modelling. To address this problem, we evaluate deconvolution method that aim to detect the clear horizontal boundaries of anomalous sources by the suppression of systematic errors. A convolution-based multilayer projection model, based on the classical 3-D gravity field forward model, is innovatively derived to model the systematic error degradation. Our deconvolution algorithm is specifically designed based on this multilayer projection model, in which three types of systematic error are defined. The degradations of the different systematic errors are considered in the deconvolution algorithm. As the primary source of degradation, the convolution-based systematic error is the main object of the multilayer projection model. Both the random systematic error and the projection systematic error are shown to form an integral part of the multilayer projection model, and the mixed norm regularization method and the primal-dual optimization method are therefore employed to control these errors and stabilize the deconvolution solution. We herein analyse the parameter identification and convergence of the proposed algorithms, and synthetic and field data sets are both used to illustrate their effectiveness. Additional synthetic examples are specifically designed to analyse the effects of the projection systematic error, which is caused by the uncertainty associated with the estimation of the impulse response function.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Investigating possible gravity change rates expected from long-term deep crustal processes in Taiwan (2014)
    Oxford University Press
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    Publication Date: 2014-06-21
    Description: We propose to test if gravimetry can prove useful in discriminating different models of long-term deep crustal processes in the case of the Taiwan mountain belt. We discuss two existing tectonic models that differ in the deep processes proposed to sustain the long-term growth of the orogen. One model assumes underplating of the uppermost Eurasian crust with subduction of the deeper part of the crust into the mantle. The other one suggests the accretion of the whole Eurasian crust above crustal-scale ramps, the lower crust being accreted into the collisional orogen. We compute the temporal gravity changes caused only by long-term rock mass transfers at depth for each of them. We show that the underplating model implies a rate of gravity change of –6 x 10 –2 μGal yr –1 , a value that increases to 2 x 10 –2 μGal yr –1 if crustal subduction is neglected. If the accretion of the whole Eurasian crust occurs, a rate of 7 x 10 –2 μGal yr –1 is obtained. The two models tested differ both in signal amplitude and spatial distribution. The yearly gravity changes expected by long-term deep crustal mass processes in Taiwan are two orders of magnitude below the present-day uncertainty of land-based gravity measurements. Assuming that these annually averaged long-term gravity changes will linearly accumulate with ongoing mountain building, multidecadal time-series are needed to identify comparable rates of gravity change. However, as gravity is sensitive to any mass redistribution, effects of short-term processes such as seismicity and surface mass transfers (erosion, sedimentation, ground-water) may prevent from detecting any long-term deep signal. This study indicates that temporal gravity is not appropriate for deciphering the long-term deep crustal processes involved in the Taiwan mountain belt.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Post-earthquake relaxation using a spectral element method: 2.5-D case (2014)
    Oxford University Press
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    Publication Date: 2014-06-21
    Description: The computation of quasi-static deformation for axisymmetric viscoelastic structures on a gravitating spherical earth is addressed using the spectral element method (SEM). A 2-D spectral element domain is defined with respect to spherical coordinates of radius and angular distance from a pole of symmetry, and 3-D viscoelastic structure is assumed to be azimuthally symmetric with respect to this pole. A point dislocation source that is periodic in azimuth is implemented with a truncated sequence of azimuthal order numbers. Viscoelasticity is limited to linear rheologies and is implemented with the correspondence principle in the Laplace transform domain. This leads to a series of decoupled 2-D problems which are solved with the SEM. Inverse Laplace transform of the independent 2-D solutions leads to the time-domain solution of the 3-D equations of quasi-static equilibrium imposed on a 2-D structure. The numerical procedure is verified through comparison with analytic solutions for finite faults embedded in a laterally homogeneous viscoelastic structure. This methodology is applicable to situations where the predominant structure varies in one horizontal direction, such as a structural contrast across (or parallel to) a long strike-slip fault.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Decadal geodetic variations in Ny-Alesund (Svalbard): role of past and present ice-mass changes (2014)
    Oxford University Press
    Details
    Publication Date: 2014-06-21
    Description: The geodetic rates for the gravity variation and vertical uplift in polar regions subject to past and present-day ice-mass changes (PDIMCs) provide important insight into the rheological structure of the Earth. We provide an update of the rates observed at Ny-Ålesund, Svalbard. To do so, we extract and remove the significant seasonal content from the observations. The rate of gravity variations, derived from absolute and relative gravity measurements, is –1.39 ± 0.11 μGal yr –1 . The rate of vertical displacements is estimated using GPS and tide gauge measurements. We obtain 7.94 ± 0.21 and 8.29 ± 1.60 mm yr –1 , respectively. We compare the extracted signal with that predicted by GLDAS/Noah and ERA-interim hydrology models. We find that the seasonal gravity variations are well-represented by local hydrology changes contained in the ERA-interim model. The phase of seasonal vertical displacements are due to non-local continental hydrology and non-tidal ocean loading. However, a large part of the amplitude of the seasonal vertical displacements remains unexplained. The geodetic rates are used to investigate the asthenosphere viscosity and lithosphere/asthenosphere thicknesses. We first correct the updated geodetic rates for those induced by PDIMCs in Svalbard, using published results, and the sea level change due to the melting of the major ice reservoirs. We show that the latter are at the level of the geodetic rate uncertainties and are responsible for rates of gravity variations and vertical displacements of –0.29 ± 0.03 μGal yr –1 and 1.11 ± 0.10 mm yr –1 , respectively. To account for the late Pleistocene deglaciation, we use the global ice evolution model ICE-3G. The Little Ice Age (LIA) deglaciation in Svalbard is modelled using a disc load model with a simple linear temporal evolution. The geodetic rates at Ny-Ålesund induced by the past deglaciations depend on the viscosity structure of the Earth. We find that viscous relaxation time due to the LIA deglaciation in Svalbard is more than 60 times shorter than that due to the Pleistocene deglaciation. We also find that the response to past and PDIMCs of an Earth model with asthenosphere viscosities ranging between 1.0 and 5.5 x 10 18 Pa s and lithosphere (resp. asthenosphere) thicknesses ranging between 50 and 100 km (resp. 120 and 170 km) can explain the rates derived from geodetic observations.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Application of the {chi}2 principle and unbiased predictive risk estimator for determining the regularization parameter in 3-D focusing gravity inversion (2014)
    Oxford University Press
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    Publication Date: 2014-11-16
    Description: The 2 principle and the unbiased predictive risk estimator are used to determine optimal regularization parameters in the context of 3-D focusing gravity inversion with the minimum support stabilizer. At each iteration of the focusing inversion the minimum support stabilizer is determined and then the fidelity term is updated using the standard form transformation. Solution of the resulting Tikhonov functional is found efficiently using the singular value decomposition of the transformed model matrix, which also provides for efficient determination of the updated regularization parameter each step. Experimental 3-D simulations using synthetic data of a dipping dike and a cube anomaly demonstrate that both parameter estimation techniques outperform the Morozov discrepancy principle for determining the regularization parameter. Smaller relative errors of the reconstructed models are obtained with fewer iterations. Data acquired over the Gotvand dam site in the south-west of Iran are used to validate use of the methods for inversion of practical data and provide good estimates of anomalous structures within the subsurface.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    Spectral-finite element approach to post-seismic relaxation in a spherical compressible Earth: application to gravity changes due to the 2004 Sumatra-Andaman earthquake (2014)
    Oxford University Press
    Details
    Publication Date: 2014-11-19
    Description: Global navigation satellite systems (GNSSs) have revealed that a mega-thrust earthquake that occurs in an island-arc trench system causes post-seismic crustal deformation. Such crustal deformation data have been interpreted by combining three mechanisms: afterslip, poroelastic rebound and viscoelastic relaxation. It is seismologically important to determine the contribution of each mechanism because it provides frictional properties between the plate boundaries and viscosity estimates in the asthenosphere which are necessary to evaluate the stress behaviour during earthquake cycles. However, the observation sites of GNSS are mostly deployed over land and can detect only a small part of the large-scale deformation, which precludes a clear separation of the mechanisms. To extend the spatial coverage of the deformation area, recent studies started to use satellite gravity data that can detect long-wavelength deformations over the ocean. To date, compared with theoretical models for calculating the post-seismic crustal deformation, a few models have been proposed to interpret the corresponding gravity variations. Previous approaches have adopted approximations for the effects of compressibility, sphericity and self-gravitation when computing gravity changes. In this study, a new spectral-finite element approach is presented to consider the effects of material compressibility for Burgers viscoelastic earth model with a laterally heterogeneous viscosity distribution. After the basic principles are explained, it is applied to the 2004 Sumatra–Andaman earthquake. For this event, post-seismic deformation mechanisms are still a controversial topic. Using the developed approach, it is shown that the spatial patterns of gravity change generated by the above three mechanisms clearly differ from one another. A comparison of the theoretical simulation results with the satellite gravity data obtained from the Gravity Recovery and Climate Experiment reveals that both afterslip and viscoelastic relaxation are occurring. Considering the spatial patterns in satellite gravity fields is an effective method for investigating post-seismic deformation mechanisms.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    The Effects of Energy Prices on Agricultural Groundwater Extraction from the High Plains Aquifer (2014)
    Oxford University Press
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    Publication Date: 2014-09-02
    Description: We examine the effects of energy prices on groundwater extraction using an econometric model of a farmer's irrigation water pumping decision that accounts for both the intensive and extensive margins. Our results show that energy prices have an effect on both types of margins. Increasing energy prices would affect crop selection decisions, crop acreage allocation decisions, and farmers’ demand for water. Our estimated total marginal effect, which sums the effects on the intensive and extensive margins, suggests that a $1 per million btu increase in the energy price would decrease water extraction by an individual farmer by 5.89 acre-feet per year, a decrease of 3.6 percent of the average annual extraction rate. Our estimated elasticity of water extraction with respect to energy price is –0.26.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q40 - General
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Do Wealth Gains from Land Appreciation Cause Farmers to Expand Acreage or Buy Land? (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-02
    Description: Recent increases in farm real estate values in the United States have increased farm equity. By exploiting periods of high and low appreciation that caused various increases in wealth for farmers owning various shares of their farmland, we examine whether U.S. grain farmers expanded their acres harvested or acres owned in response to an increase in their land wealth. We find that land wealth had little effect on farm size. However, for similarly-sized farms, a larger ownership share (10 percentage points) led to an increase in the growth of land owned (2 percentage points). Because older farmers own more of the land that they farm, greater land appreciation slows the rate at which younger farmers acquire land relative to older farmers.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Characterization of geothermally relevant structures at the top of crystalline basement in Switzerland by filters and gravity forward modelling (2014)
    Oxford University Press
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    Publication Date: 2014-08-07
    Description: Some of the major geothermal anomalies in central Europe are linked to tectonic structures within the top of crystalline basement, which modify strongly the top of this basement. Their assessment is a major challenge in exploration geophysics. Gravity has been proven to be suitable for the detection of mainly large scale lithological and structural inhomogeneities. Indeed, it is well known and proven by different wells that, for example, in northern Switzerland extended negative anomalies are linked to such structures. Due to depth limitation of wells, there vertical extension is often unknown. In this study, we have investigated the potential of gravity for the geometrical characterization of such basement structures. Our approach consists in the combination of the series of Butterworth filters, geological modelling and best-fitting between observed and computed residual anomalies. In this respect, filters of variable wavelength are applied to observed and computed gravity data. The geological model is discretized into a finite element mesh. Near-surface anomalies and the effect of the sedimentary cover were eliminated using cut-off wavelength of 10 km and geological and seismic information. We analysed the potential of preferential Butterworth filtering in a sensitivity study and applied the above mentioned approach to part of the Swiss molasses basin. Sensitivity analyses reveal that such sets of residual anomalies represents a pseudo-tomography revealing the distribution of different structures with depth. This finding allows for interpreting negative anomalies in terms of 3-D volumes. Best-fitting then permits determination of the most likely 3-D geometries of such basement structures. Our model fits both, geological observations and gravity: among 10 deep boreholes in the studied area, six reach the respective units and confirm our distribution of the negative (and positive) anomalies.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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    The role of crop land during economic development: evidence from rural Vietnam (2014)
    Oxford University Press
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    Publication Date: 2014-08-02
    Description: Under economic structural changes, some households intensify farming while others reduce it, resulting in significant changes in landholding. This paper studies the link between such changes in landholding and household well-being during a period of rapid economic transformation in Vietnam. Using a rural household panel data set, we find a U-shaped relationship between landholding and well-being: both accumulating crop land and moving out of farming are associated with higher household income and expenditure. Notably, these relationships are greater in communes that are less developed, suggesting that the benefits of structural transformation may diminish at higher levels of development.
    Keywords: I30 - General, I32 - Measurement and Analysis of Poverty, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Spherical harmonic analysis of a harmonic function given on a spheroid (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-14
    Description: A new analytical method for the computation of a truncated series of solid spherical harmonic coefficients (HCs) from data on a spheroid (i.e. an oblate ellipsoid of revolution) is derived, using a transformation between surface and solid spherical HCs. A two-step procedure is derived to extend this transformation beyond degree and order (d/o) 520. The method is compared to the Hotine–Jekeli transformation in a numerical study based on the EGM2008 global gravity model. Both methods are shown to achieve submicrometre precision in terms of height anomalies for a model to d/o 2239. However, both methods result in spherical harmonic models that are different by up to 7.6 mm in height anomalies and 2.5 mGal in gravity disturbances due to the different coordinate system used. While the Hotine–Jekeli transformation requires the use of an ellipsoidal coordinate system, the new method uses only spherical polar coordinates. The Hotine–Jekeli transformation is numerically more efficient, but the new method can more easily be extended to cases where (a linear combination of) normal derivatives of the function under consideration are given on the surface of the spheroid. It therefore provides a solution to many types of ellipsoidal boundary-value problems in the spectral domain.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Observations of ocean tidal load response in South America from subdaily GPS positions (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-29
    Description: We explore Earth's elastic deformation response to ocean tidal loading (OTL) using kinematic Global Positioning System (GPS) observations and forward-modelled predictions across South America. Harmonic coefficients are extracted from up to 14 yr of GPS-inferred receiver locations, which we estimate at 5 min intervals using precise point positioning. We compare the observed OTL-induced surface displacements against predictions derived from spherically symmetric, non-rotating, elastic and isotropic (SNREI) Earth models. We also compare sets of modelled predictions directly for various ocean-tide and Earth-model combinations. The vector differences between predicted displacements computed using separate ocean-tide models reveal uniform-displacement components common to all stations in the South America network. Removal of the network-mean OTL-induced displacements from each site substantially reduces the vector differences between observed and predicted displacements. We focus on the dominant astronomical tidal harmonics from three distinct frequency bands: semidiurnal (M 2 ), diurnal (O 1 ) and fortnightly (M f ). In each band, the observed OTL-induced surface displacements strongly resemble the modelled displacement-response patterns, and the residuals agree to about 0.3 mm or better. Even with the submillimetre correspondence between observations and predictions, we detect regional-scale spatial coherency in the final set of residuals, most notably for the M 2 harmonic. The spatial coherency appears relatively insensitive to the specific choice of ocean-tide or SNREI-Earth model. Varying the load model or 1-D elastic structure yields predicted OTL-induced displacement differences of order 0.1 mm or less for the network. Furthermore, estimates of the observational uncertainty place the noise level below the magnitude of the residual displacements for most stations, supporting our interpretation that random errors cannot account for the entire misfit. Therefore, the spatially coherent residuals may reveal deficiencies in the a priori SNREI Earth models. In particular, the residuals may indicate sensitivity to regional deviations from standard globally averaged Earth structure due to the presence of the South American craton.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    A new hybrid inversion method for parametric curved faults and its application to the 2008 Wenchuan (China) earthquake (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-20
    Description: Planar faults are widely adopted during inversions to determine slip distributions and fault geometries using geodetic observations; however, little research has been conducted with respect to curved faults. We attribute this to the lack of an appropriate parameterized modelling method. In this paper, we present a curved-fault modelling method (CFMM) that describes a curved fault according to specific parameters, and we also develop a corresponding hybrid iterative inversion algorithm (HIIA) to perform inversions for parametric curved-fault geometries and slips. The results of the strike-component and dip-component synthetic tests show that a complex S-shaped fault surface and a circular slip distribution are successfully recovered, indicating the strong performance of the CFMM and HIIA methods. In addition, we describe and verify a scenario for determining the number of necessary geometrical parameters for the HIIA and examine the case study of the Wenchuan earthquake, which occurred on a complex listric fault surface. During the iteration process of the HIIA, both the fault geometry and slip distribution of the Beichuan and Pengguan faults converge to optimal values, indicating a Beichuan fault (BCF) model with a continuous listric shape and gradual steepening from the southwest to the northeast, which is highly consistent with geological survey results. Both the synthetic and real-world case studies show that the HIIA and the CMFF are superior to the conventional fault modelling method based on rectangular planes and that these models have the potential for use in more integrated research involving inversion studies, such as joint slip/curved-fault-geometry inversions that take into account data resolving power.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Dynamics of Farmland Ownership and Leasing: Implications for Young and Beginning Farmers (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-19
    Description: This study considers the transition into farming and growth of new farmers in U.S. agriculture by examining land ownership and leasing trends. Our approach is to characterize the entire distribution by farmer age and farmer experience rather than using young versus old and beginning versus established farmer categories. We also use a linked-farms longitudinal approach to show trends over time in farmland expansion and contraction. We find that farms operated by older beginning farmers tend to be smaller and do not tend to grow over time. Our results show that it is mostly young farmers as opposed to all beginning farmers who rapidly expand their farm operations after entering agriculture. Our findings inform policy makers about the strategies that young and beginning farmers use to start their businesses and expand over time, and suggest more effective approaches for targeting loan programs to both young and beginning farmers.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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    Globally gridded terrestrial water storage variations from GRACE satellite gravimetry for hydrometeorological applications (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-22
    Description: Globally gridded estimates of monthly-mean anomalies of terrestrial water storage (TWS) are estimated from the most recent GRACE release 05a of GFZ Potsdam in order to provide non-geodetic users a convenient access to state-of-the-art GRACE monitoring data. We use an ensemble of five global land model simulations with different physics and different atmospheric forcing to obtain reliable gridded scaling factors required to correct for spatial leakage introduced during data processing. To allow for the application of this data-set for large-scale monitoring tasks, model validation efforts, and subsequently also data assimilation experiments, globally gridded estimates of TWS uncertainties that include (i) measurement, (ii) leakage and (iii) re-scaling errors are provided as well. The results are generally consistent with the gridded data provided by Tellus, but deviate in some basins which are largely affected by the uncertainties of the model information required for re-scaling, where the approach based on the median of a small ensemble of global land models introduced in this paper leads to more robust results.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Corn Area Response to Local Ethanol Markets in the United States: A Grid Cell Level Analysis (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-24
    Description: We measure corn and total agricultural area response to the biofuels boom in the United States from 2006 to 2010. Specifically, we use newly available micro-scale grid cell data to test whether a location's corn and total agricultural cultivation rose in response to the capacity of ethanol refineries in their vicinity. Based on these data, acreage in corn and overall agriculture not only grew in already-cultivated areas but also expanded into previously uncultivated areas. Acreage in corn and total agriculture also correlated with proximity to ethanol plants, though the relationship dampened over the time period. A formal estimation of the link between acreage and ethanol refineries, however, must account for the endogenous location decisions of ethanol plants and areas of corn supply. We present historical evidence to support the use of the US railroad network as a valid instrument for ethanol plant locations. Our estimates show that a location's neighborhood refining capacity exerts strong and significant effects on acreage planted in corn and total agricultural acreage. The largest impacts of ethanol plants were felt in locations where cultivation area was relatively low. This high-resolution evidence of ethanol impacts on local agricultural outcomes can inform researchers and policy-makers concerned with crop diversity, environmental sustainability, and rural economic development.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q16 - R&D ; Agricultural Technology ; Agricultural Extension Services
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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    Exchanging Land for Solidarity: Solidarity Transfers among Voluntarily Resettled and Non-resettled Land-Reform Beneficiaries (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-24
    Description: Mutual aid among villagers in developing countries is often the only means of insuring against economic shocks. We use "lab-in-the-field experiments" in Cambodian villages to study solidarity in established and newly resettled communities. Our experimental participants were part of an agricultural land-distribution project for which they signed up voluntarily. Half of our sample voluntarily resettled one and a half years before this study. Playing a version of the "solidarity game," we identify the effect of voluntary resettlement on willingness to help anonymous fellow villagers. We find that resettled farmers transfer substantially less money to their fellow villagers than farmers who have not resettled. Our experimental results indicate greater vulnerability on the part of resettled households in the initial years after resettlement.
    Keywords: C93 - Field Experiments, D03 - Behavioral Economics ; Underlying Principles, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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    Does the Minimum Lot Size Program Affect Farmland Values? Empirical Evidence Using Administrative Data and Regression Discontinuity Design in Taiwan (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-24
    Description: This study empirically assesses the causal effect of the minimum lot size program on farmland values in Taiwan. A unique dataset of 4,032 parcels of farmland drawn from administrative foreclosure auction profiles between 2000 and 2008 and regression discontinuity design were applied to cope with the endogeneity issue of land use regulations. The results of the parametric and nonparametric estimations indicate that the minimum lot size program significantly increases farmland value by approximately 18% and 15%, respectively. Moreover, the program effect is more pronounced for farmland located in urban/suburban areas. In the absence of a tax effect and externality resulting from non-agricultural activities, the significant program effect on farmland values is likely to result from the effect of the program on farmland's option value for future development.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, R52 - Land Use and Other Regulations
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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    A Novel, Spatiotemporally Explicit Ecological-economic Modeling Procedure for the Design of Cost-effective Agri-environment Schemes to Conserve Biodiversity (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-31
    Description: Agri-environment schemes (AES) compensate farmers for land use measures that are costly to them but beneficial to biodiversity and the environment. We present an ecological-economic modeling procedure for the design of cost-effective AES to conserve grassland biodiversity, which is applicable to large areas, covers many endangered species and grassland types, and includes several hundred different types of mowing regimes, grazing regimes, and combinations of mowing and grazing regimes as land use measures. The modeling procedure also accounts for the spatial variations in the land use measures' costs and in the effects on species and grassland types. The procedure's main novelty is that it considers variations of the costs and impacts on species and grassland types that arise from different timings of the land use measures. Considering the spatial and the temporal dimension of land use measures makes the modeling procedure spatiotemporally explicit. We demonstrate the power of the modeling procedure by evaluating an existing grassland AES in Saxony, Germany, and identify substantial improvements in terms of cost-effectiveness.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q57 - Ecological Economics: Ecosystem Services ; Biodiversity Conservation ; Bioeconomics
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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    Regional recovery of the disturbing gravitational potential by inverting satellite gravitational gradients (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-10
    Description: Regional recovery of the disturbing gravitational potential in the area of Central Europe from satellite gravitational gradients data is discussed in this contribution. The disturbing gravitational potential is obtained by inverting surface integral formulas which transform the disturbing gravitational potential onto disturbing gravitational gradients in the spherical local north-oriented frame. Two numerical approaches that solve the inverse problem are considered. In the first approach, the integral formulas are rigorously decomposed into two parts, that is, the effects of the gradient data within near and distant zones. While the effect of the near zone data is sought as an inverse problem, the effect of the distant zone data is synthesized from the global gravitational model GGM05S using spectral weights given by truncation error coefficients up to the degree 150. In the second approach, a reference gravitational field up to the degree 180 is applied to reduce and smooth measured gravitational gradients. In both cases we recovered the disturbing gravitational potential from each of the four well-measured gravitational gradients of the GOCE satellite separately as well as from their combination. Obtained results are compared with the EGM2008, DIR-r2, TIM-r2 and SPW-r2 global gravitational models. The best fit was achieved for EGM2008 and the second approach combining all four well-measured gravitational gradients with rms of 1.231 m 2  s –2 .
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Efficient modelling of gravity effects due to topographic masses using the Gauss-FFT method (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-12
    Description: We present efficient Fourier-domain algorithms for modelling gravity effects due to topographic masses. The well-known Parker's formula originally based on the standard fast Fourier transform (FFT) algorithm is modified by applying the Gauss–FFT method instead. Numerical precision of the forward and inverse Fourier transforms embedded in Parker's formula and its extended forms are significantly improved by the Gauss–FFT method. The topographic model is composed of two major aspects, the geometry and the density. Versatile geometric representations, including the mass line model, the mass prism model, the polyhedron model and smoother topographic models interpolated from discrete data sets using high-order splines or pre-defined by analytical functions, in combination with density distributions that vary both laterally and vertically in rather arbitrary ways following exponential or general polynomial functions, now can be treated in a consistent framework by applying the Gauss–FFT method. The method presented has been numerically checked by space-domain analytical and hybrid analytical/numerical solutions already established in the literature. Synthetic and real model tests show that both the Gauss–FFT method and the standard FFT method run much faster than space-domain solutions, with the Gauss–FFT method being superior in numerical accuracy. When truncation errors are negligible, the Gauss–FFT method can provide forward results almost identical to space-domain analytical or semi-numerical solutions in much less time.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Inversion of gravity gradient tensor data: does it provide better resolution? (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-14
    Description: The gravity gradient tensor (GGT) has been increasingly used in practical applications, but the advantages and the disadvantages of the analysis of GGT components versus the analysis of the vertical component of the gravity field are still debated. We analyse the performance of joint inversion of GGT components versus separate inversion of the gravity field alone, or of one tensor component. We perform our analysis by inspection of the Picard Plot, a Singular Value Decomposition tool, and analyse both synthetic data and gradiometer measurements carried out at the Vredefort structure, South Africa. We show that the main factors controlling the reliability of the inversion are algebraic ambiguity (the difference between the number of unknowns and the number of available data points) and signal-to-noise ratio. Provided that algebraic ambiguity is kept low and the noise level is small enough so that a sufficient number of SVD components can be included in the regularized solution, we find that: (i) the choice of tensor components involved in the inversion is not crucial to the overall reliability of the reconstructions; (ii) GGT inversion can yield the same resolution as inversion with a denser distribution of gravity data points, but with the advantage of using fewer measurement stations.
    Keywords: Gravity, Geodesy and Tides
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Profit-Maximizing Land-Use Revisited: The Testable Implications of Non-joint Crop Production Under Land Constraint (2013)
    Oxford University Press
    Details
    Publication Date: 2013-11-22
    Description: This article derives new implications for the land allocation and production decisions of profit-maximizing farm-firms where production of different crops is non-joint but subject to a constraint on the total land area. These implications are observable and thus subject to empirical scrutiny. An estimable model of crop production, land allocation, and input-use decisions is derived that permits joint production and enables the implications of non-joint but land-constrained production to be tested. This may improve econometric estimates of cross-price elasticities of supply by linking models of land use and production decisions, and allowing non-jointness to be imposed where appropriate.
    Keywords: Q11 - Aggregate Supply and Demand Analysis ; Prices, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Comparison of GHG-Emission Indicators for Dairy Farms with Respect to Induced Abatement Costs, Accuracy, and Feasibility (2013)
    Oxford University Press
    Details
    Publication Date: 2013-11-22
    Description: There is broad debate about including agriculture in greenhouse gas (GHG) reduction efforts such as the European Emissions Trading Scheme. Since most agricultural GHG emissions originate from non-point sources, they cannot be directly measured, and therefore have to be derived by calculation schemes (indicators). We designed five such GHG indicators for dairy farms and analyzed the trade-offs between their feasibility, measurement accuracy, and level of induced abatement costs. Analyses of induced abatement costs and calculation accuracy are based on emission reduction simulations with a highly-detailed single-farm optimization model. Feasibility is discussed in a qualitative manner. Our results indicate that the trade-offs depend on both farm characteristics and the targeted reduction level. In particular, the advantages of detailed indicators decrease for higher abatement levels. Only the least feasible indicator led to abatement costs that would result in emission efforts at given prices in the European Emissions Trading Scheme, although with a rather small potential. Our results thus suggest little potential for including dairy production into market-based reduction policies.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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