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  • 1
    Series available for loan
    Series available for loan
    Gravity field mapping from a combination of satellite altimetry and sea gravimetry in the Mediterranean Sea (1996)
    Masala
    Associated volumes
    Details Availability
    Call number: SR 90.0085(96,1)
    In: Reports of the Finnish Geodetic Institute
    Type of Medium: Series available for loan
    Pages: 22 S.
    ISBN: 9517111924
    Series Statement: Reports of the Finnish Geodetic Institute 96,1
    Language: English
    Location: Lower compact magazine
    Branch Library: GFZ Library
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  • 2
    Electronic Resource
    Electronic Resource
    Combination of Ers-1 and Topex Altimetry For Precise Geoid and Gravity Recovery In the Mediterranean Sea (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 125 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: From the separate processing and crossover analysis of repeat ERS-1 and TOPEX altimeter data in the Mediterranean basin it was assessed that the TOPEX data are characterized by higher accuracy than that of ERS-1 and other previous missions’ data. It is also known from the coverage of both missions that the resolution of ERS-1 data is superior to that of the TOPEX data, since the distance across track in the TOPEX mission is about four times the corresponding distance in the ERS-1 mission for the 35-day repeat. Therefore, taking into account the advantages and drawbacks of both missions, a common adjustment of both altimeter data sources was carried out in order to improve the prediction accuracy of gravity anomalies and geoid heights in the Mediterranean Sea. the computed sea-surface heights (SSHs) have been used in the following two trials.The first one was the recovery of sea gravity anomalies by an inversion of the adjusted altimeter data. the prediction of gravity anomalies has been performed in three individual test subareas of the Mediterranean Sea, located in the western, central and eastern parts, respectively. the method used was the flexible least-squares collocation (LSC) procedure. In order to assess the quality of the recovered gravity anomalies an external comparison was made with observed (control) gravity values. the standard deviation (sd) of the differences was found to vary from 13.4 mGal in the eastern test subarea to 6.5 mGal in the western subarea. In the central test subarea the sd of the corresponding differences reached a level of 5.8 mGal. the second test run comprised comparisons between the adjusted SSHs and the corresponding gravimetric geoidal heights in order to obtain a rough estimation of the sea-surface topography (SST) in the Mediterranean Sea. the gravimetric geoidal heights have been derived from sea gravity data in the western and central test subareas using the fast leastsquares collocation (FLSC), the 2-D planar fast fourier transform (PFFT) and the 2-D spherical FFT (SFFT) methods. In the eastern test area the LSC approach was used due to the irregular distribution of the gravity data. the computed gravimetric geoid heights have been compared with the corresponding SSHs in the three aforementioned test subareas. the sd of the differences was found to vary from 55 cm in the eastern test subarea to 7 cm in the central subarea. In the western test subarea the sd of the corresponding differences reached a level of 12 cm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb06551.x
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  • 3
    Electronic Resource
    Electronic Resource
    Gravity-field improvement in the Mediterranean Sea by estimating the bottom topography using collocation (1998)
    Springer
    Journal of geodesy 72 (1998), S. 136-143 
    Details
    ISSN: 1432-1394
    Keywords: Key words. Gravity inversion ; Bottom topography ; Least-squares Collocation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. The contribution of bathymetry to the prediction of quantities related to the gravity field (e.g., gravity anomalies, geoid heights) is discussed in an extended test area of the central Mediterranean Sea. Sea gravity anomalies and a priori statistical characteristics of depths are used in a least-squares collocation procedure in order to produce new depths, giving a better smoothing of the gravity field when using a remove-restore procedure. The effect of the bottom topography on gravity-field modeling is studied using both the original and the new depths through a residual terrain modeling reduction. The numerical tests show a considerable smoothing of the sea gravity anomalies and the available altimeter heights when the new depth information is taken into account according to the covariance analysis performed. Moreover, geoid heights are computed by combining the sea gravity anomalies either with the original depths or with the new ones, using as a reference surface the OSU91A geopotential model. Comparing the computed geoid heights with adjusted altimeter sea-surface heights (SSHs), better results are obtained when subtracting the attraction of the new depth information. Similar results are obtained when predicting gravity anomalies from altimeter SSHs where the terrain effect on altimetry is based on the new bottom topography.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001900050155
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  • 4
    Electronic Resource
    Electronic Resource
    Validation of ETOPO5U in the Hellenic area (1994)
    Springer
    Journal of geodesy 68 (1994), S. 88-99 
    Details
    ISSN: 1432-1394
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract Mean 5′ × 5′ heights and depths from ETOPO5U (Earth Topography at 5′ spacing Updated) Digital Terrain Model (DTM) were compared with corresponding quantities of a local DTM in the test area [38°≤ φ ≤ 40°, 21°≤ λ ≤ 24°]. From this comparison a shift of ETOPO5U with respect to the local DTM in the longitudinal direction equal to 5 min was found after applying an efficient fast Fourier transform (FFT) technique. Furthermore, sparse mean height differences larger than 1,000 m were observed between ETOPO5U and the local DTM due rather to errors of ETOPO5U. The effect of these errors on gravity and height anomalies was computed in a subregion of the area under consideration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00819385
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  • 5
    Electronic Resource
    Electronic Resource
    Calibration of satellite gradiometer data aided by ground gravity data (1998)
    Springer
    Journal of geodesy 72 (1998), S. 617-625 
    Details
    ISSN: 1432-1394
    Keywords: Key words. Satellite gradiometer data ; Parametric collocation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. Parametric least squares collocation was used in order to study the detection of systematic errors of satellite gradiometer data. For this purpose, simulated data sets with a priori known systematic errors were produced using ground gravity data in the very smooth gravity field of the Canadian plains. Experiments carried out at different satellite altitudes showed that the recovery of bias parameters from the gradiometer “measurements” is possible with high accuracy, especially in the case of crossing tracks. The mean value of the differences (original minus estimated bias parameters) was relatively large compared to the standard deviation of the corresponding second-order derivative component at the corresponding height. This mean value almost vanished when gravity data at ground level were combined with the second-order derivative data set at satellite altitude. In the case of simultaneous estimation of bias and tilt parameters from ∂2 T/∂z 2“measurements”, the recovery of both parameters agreed very well with the collocation error estimation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001900050201
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  • 6
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    The exploitation of state of the art digital terrain databases and combined or satellite-only Earth gravity models for the estimation of the crust-mantle interface over oceanic regions (2013)
    Oxford University Press
    Details
    Publication Date: 2013-05-09
    Description: The prediction of the geometry of characteristic crustal interfaces, such as bathymetry or Moho, can be carried out efficiently by applying well tested estimation procedures. The computation of the gravity response at the Earth's surface of a characteristic density layer in the Earth's interior in combination with the statistical tool of Least Squares Collocation have been proven to be a flexible and useful prediction tool, especially at regions with lack in primary crustal observations. To investigate the contribution of recently released digital terrain databases to this estimation procedure we use the one-minute global elevation databases GEBCO and TOPO14. Using the combined Earth gravity model EGM2008 and recently released GOCE-only models we produce the observed grid of gravity anomalies over two test areas in the Indian and the Atlantic oceans. The estimation procedure is based on a two-layer model of the upper crust and is driven mainly by the definition and quality of the involved covariance functions. The application leads to independent and much denser estimations of the crust–mantle interface over these regions, in comparison with the available Moho information provided by global databases such as CRUST 2.0. Apart from the direct comparison between the obtained solutions a further assessment was carried out in terms of computing the corresponding isostatic effects on the available regional altimeter data.
    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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    Gravity field approximation using airborne gravity gradiometer data (1992)
    American Geophysical Union
    Details
    Publication Date: 1992-01-01
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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  • 8
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    Regional recovery of the gravity field from satellite gravity gradiometer and gravity vector data using collocation (1995)
    American Geophysical Union
    Details
    Publication Date: 1995-11-10
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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  • 9
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    TEC variations over the Mediterranean during the seismic activity period of the last quarter of 2005 in the area of Greece (2008)
    Copernicus
    Details
    Publication Date: 2008-11-25
    Description: In this paper the Total Electron Content (TEC) data of eight Global Positioning System (GPS) stations of the EUREF network (AUT1, Thessaloniki, TUC2, Crete in Greece, MATE, Matera, LAMP, Lampedusa in Italy, GAIA, in Portugal, RABT, Rabat, EVPA, Evpatoria in Ukrain and TRAB, Trabson in Turkey) were analysed using wavelet analysis in order to detect any frequency dependence of the correlation between TEC over different stations. In the same time frequency dependence of Dst (Global geomagnetic field disturbances) and TEC variations over each GPS station are searched in order to detect any correlation between them. The main conclusion of this analysis is that the components of TEC variation with periods
    Print ISSN: 1561-8633
    Electronic ISSN: 1684-9981
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 10
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    Atmospheric tide disturbances as Earthquake precursory phenomena (2004)
    Copernicus
    Details
    Publication Date: 2004-03-01
    Description: The tidal changes of the barometric pressure in the area of Thessaloniki were studied by analysing a sample of 21 years of hourly measurements. The resulted tidal parameters (amplitude and phase difference) were considered as "mean values" of the corresponding parameters for this long time period. Using these parameters, barometric changes were computed and subtracted from the observations. Assuming that the residuals might include local (in terms of time) information,the residual time series was split in 21 blocks and a new analysis was performed for each block separately. The 21 amplitude values computed for each tidal wave were considered as the amplitude variation with respect to the correspondingmean value. An observable correlation of the amplitude exalting of the most of the tidal waves was found to Earthquakes of magnitude 〉4, occurred close to Thessaloniki in the test period.
    Print ISSN: 1561-8633
    Electronic ISSN: 1684-9981
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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