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  • 1
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    Treatment of ocean tide aliasing in the context of a next generation gravity field mission (2018)
    Oxford University Press
    Details
    Publication Date: 2018-04-12
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 2
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    Joint inversion estimate of regional glacial isostatic adjustment in Antarctica considering a lateral varying Earth structure (ESA STSE Project REGINA) (2017)
    Oxford University Press
    Details
    Publication Date: 2017-08-29
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 3
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    The tree-canopy effect in gravity forward modelling (2019)
    Oxford University Press
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    Publication Date: 2019-06-07
    Description: SUMMARY High resolution and accurate digital terrain models (DTMs) are frequently used as input data sets to define the topographic masses in gravity forward modelling, for example, for terrain corrections in the context of regional gravity modelling. However, over vegetated areas such as forests and scrublands, the radar- and image-based digital elevation models (DEMs) may contain a tree bias, and therefore do not represent the bare-ground surface. The presence of vegetation-induced signals in DEMs, denoted here the tree-canopy effect, will introduce errors in the gravity forward modelling. In this study, the role of the tree-canopy effect in gravity forward modelling calculations is numerically investigated. First, spectral forward modelling techniques were applied to analyse a global tree-canopy bias model with a horizontal resolution of 1 km x 1 km and to quantify its effect on global gravity forward modelling results. We demonstrate that tree-canopy signals in the DEM produce a positive bias in the topographic gravitational field over vegetated areas, with values ranging from 0 to ∼2.7 mGal for gravity disturbances. Second, the role of the tree-canopy effect in high-frequency gravity forward modelling is studied using well-known residual terrain modelling (RTM) techniques. As DEM data sets, we used the 3″ SRTM (Shuttle Radar Topography Mission Digital 9 m Elevation Database) V4.1 (containing vegetation biases) and the 3″ MERIT-DEM (Multi-Error-Removed Improved-Terrain Digital elevation model) as a representation of the bare-ground elevations. Using Tasmania and the Amazon rainforest regions as test areas with significant tree-canopy signals we show that the tree-height effect on RTM calculations is of high-frequency nature, with rather small signals which reach in extreme cases amplitudes of ∼1–2 mGal occurring at forest boundaries. Third, using ground gravity observations, validation experiments were performed over the Australian Alps, Tasmania and the Canadian Rocky Mountains. All validation experiments show that the bare-ground elevation model MERIT-DEM performs better than SRTM V4.1 in terms of reduction of the discrepancies between modelled and observed gravity values. As a general conclusion, bare-ground DEM models should be preferred in any gravity forward modelling application to avoid or reduce the tree-canopy effect.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 4
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    Next generation gravity missions: near-real time gravity field retrieval strategy (2019)
    Oxford University Press
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    Publication Date: 2019-02-13
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 5
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    A new method of improving global geopotential models regionally using GNSS/levelling data (2020)
    Oxford University Press
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    Publication Date: 2020-02-03
    Description: In this paper, a new method for regionally improving global geopotential models (GGMs) with global navigation satellite system (GNSS)/levelling data is proposed. In this method, the GNNS/levelling data are at first converted to disturbing potential data with inverse Bruns’ formula. Then the systematic errors in disturbing potential data are removed with a three-parameter correction surface. Afterwards, the disturbing potential data on the Earth's surface are downward continued to the surface of an inner sphere with inverse Poisson's integral equation. Global disturbing potential data on the whole sphere could be achieved with combination of the downward continued data and the GGM-derived data. At last, the final regionally improved geopotential model (RIGM) could be recovered from the disturbing potential data using least-squares method. Four RIGM models for Qingdao (QD) are determined based on four different sets of GNSS/levelling data points to validate the capability of the method. The standard deviation of height anomaly errors of RIGM-QDs are nearly 25 and 30 per cent on average smaller than Earth Gravity Model 2008 (EGM2008) on checkpoints and data points, respectively. This means that the RIGM-QDs fit better to the GNSS/levelling network in this area than EGM2008. The results show that the proposed method is successful at improving GGMs in regional area with regional GNSS/levelling data.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 6
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    Consistent quantification of the impact of key mission design parameters on the performance of next-generation gravity missions (2020)
    Oxford University Press
    Details
    Publication Date: 2020-02-05
    Description: The GRACE and GRACE-FO missions have been observing time variations of the Earth's gravity field for more than 15 yr. For a possible successor mission, the need to continue mass change observations have to be balanced with the ambition for monitoring capabilities with an enhanced spatial and temporal resolution that will enable improved scientific results and will serve operational services and applications. Various study groups performed individual simulations to analyse different aspects of possible NGGMs from a scientific and technical point of view. As these studies are not directly comparable due to different assumptions regarding mission design and instrumentation, the goal of this paper is to systematically analyse and quantify the key mission parameters (number of satellite pairs, orbit altitude, sensors) and the impact of various error sources (AO, OT models, post-processing) in a consistent simulation environment. Our study demonstrates that a single-pair mission with laser interferometry in a low orbit with a drag compensation system would be the only possibility within the single-pair options to increase the performance compared to the GRACE/GRACE-FO. Tailored post-processing is not able to achieve the same performance as a double-pair mission without post-processing. Also, such a mission concept does not solve the problems of temporal aliasing due to observation geometry. In contrast, double-pair concepts have the potential to retrieve the full AOHIS signal and in some cases even double the performance to the comparable single-pair scenario. When combining a double-pair with laser interferometry and an improved accelerometer, the sensor noise is, apart from the ocean tide modelling errors, one of the limiting factors. Therefore, the next big step for observing the gravity field globally with a satellite mission can only be taken by launching a double pair mission. With this quantification of key architecture features of a future satellite gravity mission, the study aims to improve the available information to allow for an informed decision making and give an indication of priority for the different mission concepts.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 7
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    The experimental gravity field model XGM2016 (2017)
    GFZ Data Services
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    Publication Date: 2021-09-02
    Description: Abstract
    Description: The experimental gravity field model XGM2016 is an outcome of TUM's assessment of a 15'x15' data grid excerpt provided from NGA's updated and revised gravity data base. The assessment shall support NGA's efforts on the way on the way to the Earth Gravity Model EGM2020.
    Description: Other
    Description: XGM2016 is a combination model based on the satellite-only gravity field model GOCO05s and a global 15'x15' data grid provided from NGA's data base.
    Keywords: ICGEM ; global gravitational model ; GOCO ; Geodesy ; GOCE
    Language: English
    Type: Dataset , Dataset
    Format: 15478728 Bytes
    Format: 4 Files
    Format: application/x-zip-compressed
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  • 8
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    The experimental gravity field model XGM2019e (2019)
    GFZ Data Services
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    Publication Date: 2021-09-02
    Description: Abstract
    Description: XGM2019e is a combined global gravity field model represented through spheroidal harmonics up to d/o 5399, corresponding to a spatial resolution of 2’ (~4 km). As data sources it includes the satellite model GOCO06s in the longer wavelength area combined with terrestrial measurements for the shorter wavelengths. The terrestrial data itself consists over land and ocean of gravity anomalies provided by courtesy of NGA (identical to XGM2016, having a resolution of 15’) augmented with topographically derived gravity over land (EARTH2014). Over the oceans, gravity anomalies derived from satellite altimetry are used (DTU13, in consistency with the NGA dataset).The combination of the satellite data with the terrestrial observations is performed by using full normal equations up to d/o 719 (15’). Beyond d/o 719, a block-diagonal least-squares solution is calculated for the high-resolution terrestrial data (from topography and altimetry). All calculations are performed in the spheroidal harmonic domain.In the spectral band up to d/o 719 the new model shows over land a slightly improved behavior over preceding models such as XGM2016, EIGEN6c4 or EGM2008 when comparing it to independent GPS leveling data. Over land and in the spectral range above d/o 719 the accuracy of XGM2019e suffers from the sole use of topographic forward modelling; Hence, errors are increased in well-surveyed areas compared to models containing real gravity data, e.g. EIGEN6c4 or EGM2008. However, the performance of XGM2019e can be considered as globally more homogeneous and independent from existing high resolution global models. Over the oceans the model exhibits an improved performance throughout the complete spectrum (equal or better than preceding models).
    Keywords: geodesy ; global gravity field model ; ICGEM ; GOCO ; GOCE ; EARTH SCIENCE 〉 SOLID EARTH 〉 GEODETICS 〉 GEOID CHARACTERISTICS ; EARTH SCIENCE 〉 SOLID EARTH 〉 GRAVITY/GRAVITATIONAL FIELD 〉 GRAVITY
    Language: English
    Type: Dataset , Dataset
    Format: 6 Files
    Format: application/octet-stream
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  • 9
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    The polar extended gravity field model TIM_R6e (2019)
    GFZ Data Services
    Details
    Publication Date: 2021-09-02
    Description: Abstract
    Description: TIM_R6e is an extended version of the satellity-only global gravity field model TIM_R6 (Brockmann et al., 2019) which includes additional terrestrial gravity field observations over GOCE's polar gap areas. The included terrestrial information consists of the PolarGap campaign data (Forsberg et al., 2017) augumented by the AntGG gravity data compilation (Scheinert et al., 2016) over the southern polar gap (〉83°S) and the ArcGP data (Forsberg et al. 2007) over the northern polar gap (〉83°N). The combination is performed on normal equation level, encompassing the terrestrial data as spectrally limited geographic 0.5°x0.5° grids over the polar gaps.
    Description: TechnicalInfo
    Description: Processing procedures: (extending TIM_R6)Gravity from orbits (SST): (identical to TIM_R6)- short-arc integral method applied to kinematic orbits, up to degree/order 150- orbit variance information included as part of the stochastic model, it is refined by empirical covariance functionsGravity from gradients (SGG): (identical to TIM_R6)- parameterization up to degree/order 300- observations used: Vxx, Vyy, Vzz and Vxz in the Gradiometer Reference Frame (GRF)- realistic stochastic modelling by applying digital decorrelation filters to the observation equations; estimated separately for individual data segments applying a robust procedureGravity from terrestrial observations (TER):- collocation of the original terrestrial data sources onto 30'x30' geographic gravity disturbance grids (in the polar gap areas above 83° southern/northern latitude, thus forming a pair of polar caps)- spectral limitation of the data to D/O 300 within the collocation process- the chosen grid is fully compatible with the grid of the zero observation constraints of the original TIM_R6 model. In its function it replaces the original constraints- from the collocated polar caps, a partial normal equation system, up to D/O 300 is derivedCombined solution:- addition of normal equations (SST D/O 150, SGG D/O 300, TER D/O 300)- Constraints: * Kaula-regularization applied to coefficients of degrees/orders 201 - 300 (constrained towards zero, fully compatible with TIM_R6)- weighting of SST and SGG is identical to TIM_R6. All TER observations are weighted with 5 mGal.Specific features of resulting gravity field:- Gravity field solution is (mostly) independent of any other gravity field information (outside the polar gap region)- Constraint towards zero starting from degree/order 201 to improve signal-to-noise ratio- Related variance-covariance information represents very well the true errors of the coefficients (outside the polar gap region)- Solution can be used for independent comparison and combination on normal equation level with other satellite-only models (e.g. GRACE), terrestrial gravity data, and altimetry (outside the polar gap region)- Since in the low degrees the solution is based solely on GOCE orbits, it is not competitive with a GRACE model in this spectral region (outside the polar gap region)- In comparison to TIM_R6, TIM_R6e should deliver more accurate results, especially towards the polar gaps. However, as it uses additional data sources it cannot be seen as totally independent anymore: even outside the polar gap regions correlations (introduced by the holistic nature of spherical harmonics) may be found.
    Keywords: global gravitational model ; ICGEM ; GOCE ; PolarGap ; geodesy ; EARTH SCIENCE 〉 SOLID EARTH 〉 GEODETICS 〉 GEOID CHARACTERISTICS ; EARTH SCIENCE 〉 SOLID EARTH 〉 GRAVITY/GRAVITATIONAL FIELD 〉 GRAVITY
    Language: English
    Type: Dataset , Dataset
    Format: 3 Files
    Format: application/octet-stream
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  • 10
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    The satellite-only gravity field model GOCO06s (2019)
    GFZ Data Services
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    Publication Date: 2021-09-02
    Description: Abstract
    Description: GOCO06s is a satellite-only, global gravity field model up to degree and order 300, with secular and annual variations up to degree and order 120. It was produced by the GOCO Team (Technical University of Munich, University of Bonn, Graz University of Technology, Austrian Academy of Sciences, University of Bern) and is based on 1,160,000,000 observations from 19 satellites. The contributing satellite mission are: GOCE (TIM6 gradiometer observations), GRACE (ITSG-Grace2018s), kinematic orbits from Swarm A+B+C, TerraSAR-X, TanDEM-X, CHAMP, GRACE and GOCE, and SLR observations to LAGEOS, LAGEOS 2, Starlette, Stella, AJISAI, LARES, LARETS, Etalon 1/2 and BLITS. The combination of the individual data sources is performed on the basis of the full systems of normal equations, where the relative weighting between each constituent is determined by variance component estimation. In order to account for the polar gap of GOCE, the solution is Kaula-regularized after degree and order 150.The model is available via the ICGEM Service (Ince et al., 2019)
    Description: TechnicalInfo
    Description: PARAMETERS:modelname GOCO06sproduct_type gravity_fieldearth_gravity_constant 3.9860044150e+14radius 6.3781363000e+06max_degree 300norm fully_normalizedtide_system zero_tideerrors formal
    Keywords: ICGEM ; global gravitational model ; GOCO ; GOCE ; GRACE ; EARTH SCIENCE 〉 SOLID EARTH 〉 GRAVITY/GRAVITATIONAL FIELD 〉 GRAVITATIONAL FIELD ; EARTH SCIENCE 〉 SOLID EARTH 〉 GEODETICS 〉 GEOID CHARACTERISTICS
    Type: Dataset
    Format: 4 Files
    Format: application/octet-stream
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