Evaluation of the accuracy of the EIGEN-1S and -2 CHAMP-derived gravity field models by satellite crossover altimetry |
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| Authors: | J Klokoník J Kostelecký CA Wagner P Schwintzer Ch Förste and R Scharroo |
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| Institution: | (1) CEDR—Astronomical Institute of the Academy of Sciences of the Czech Republic, CZ-251 65 Ond ejov Observatory, Czech Republic;(2) CEDR—Research Institute of Geodesy, Topography and Cartography, CZ-250 66 Zdiby 98, Czech Republic;(3) Department of Higher Geodesy, Czech Technical University, CZ-166 29 Prague 6, Thákurova 7, Czech Republic;(4) NOAA/NESDIS, Laboratory for Satellite Altimetry, East–West Highway, Silver Spring, MD 20910, USA;(5) Dept. 1:  Geodesy and Remote Sensing , GeoForschungsZentrum Potsdam (GFZ), Telegrafenberg A17, D-14473 Potsdam, Germany;(6) Delft Institute for Earth-Oriented Space Research (DEOS), Delft University of Technology, Kluyverweg 1, 2629, HS, Delft, The Netherlands |
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| Abstract: | Since the advent of CHAMP, the first in a series of low-altitude satellites being almost continuously and precisely tracked by GPS, a new generation of long-wavelength gravitational geopotential models can be derived. The accuracy evaluation of these models depends to a large extent on the comparison with external data of comparable quality. Here, two CHAMP-derived models, EIGEN-1S and EIGEN-2, are tested with independent long-term-averaged single satellite crossover (SSC) sea heights from three altimetric satellites (ERS-1, ERS-2 and Geosat). The analyses show that long-term averages of crossover residuals still are powerful data to test CHAMP gravity field models. The new models are tested in the spatial domain with the aid of ERS-1/-2 and Geosat SSCs, and in the spectral domain with latitude-lumped coefficient (LLC) corrections derived from the SSCs. The LLC corrections allow a representation of the satellite-orbit-specific error spectra per order of the model s spherical harmonic coefficients. These  observed LLC corrections are compared to the LLC projections from the models variance–covariance matrix. The excessively large LLC errors at order 2 found in the case of EIGEN-2 with the ERS data are discussed. The degree-dependent scaling factors for the variance-covariance matrices of EIGEN-1S and –2, applied to obtain more realistic error estimates of the solved-for coefficients, are compatible with the results found here. |
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| Keywords: | Gravity field models Accuracy assessment Satellite crossover altimetry Latitude-lumped coefficients CHAMP |
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