Maps of Altimetric Gravity Based on ERS-1 Geodetic Phase Data
Maps of high-resolution gravity anomalies are derived from vertical deflection grids, which are computed in a first solution from a high-density ERS-1 mean sea surface height model. For generation of high-quality sea surface heights, GFZ/D-PAF has reprocessed the ESA standard altimeter product (ERS.ALT.OPRO2). This process includes improved orbit calculation, the replacement of standard geophysical corrections and the application of additional range corrections. A second solution is based on the computation of vertical deflections derived from gradients of the 1-Hz altimeter measurements in order to keep the high frequency signal of the original data.
The computation of gravity anomalies from deflections of the vertical is performed by the 2-dimensional Fast-Fourier transformation (FFT), which is based on the plane approximation of the earth. The error due to this assumption can be minimized by first subtracting a long wavelength spherical harmonic geoid model from the gridded sea surface heights, before generating the vertical deflection grids. The gravity anomalies now result from addition and multiplication operations of the Fourier transformed vertical deflections, followed by the inverse FFT. A piecewise application of this method combined with the elimination of the edges of each computation area suppresses truncation effects. To obtain the final result, the long wavelength part is added back to the computed residual gravity anomalies.
A global map of gravity anomalies was generated which served as one of the input data sets for computing the high-resolution gravity model GFZ96. Quality tests are performed for an area along the Mid-Atlantic Ridge (30.5°–36.5°S), where the altimetric derived anomalies from both solutions are compared with anomalies from the gravity maps of Marks et al.  and of Smith & Sandwell , and additional with validated shipboard gravity data [Neumann et al. 1993].
KeywordsGravity Field Gravity Anomaly Vertical Deflection Altimeter Measurement South American Plate
Unable to display preview. Download preview PDF.
- Anzenhofer M., Gruber Th., and Reigber Ch. (1997); Fully reprocessed ERS-1 altimeter data from 1992 to 1995: reflection of sea level change; submitted to Journal of Geophysical Research (ERS special issue).Google Scholar
- Gruber Th. and Anzenhofer M. (1993); The GFZ 360 gravity field model; Proceedings of Session G3, European Geophysical Society XV III General Assembly, ed: Forsberg R., Denker H., Geodetic Division, Kort-og Matrikelstyrelsen, Copenhagen.Google Scholar
- Gruber Th., Anzenhofer M., and Rentsch M. (1996); The 1995 GFZ High Resolution Gravity Model; Global Gravity Field and Its Temporal Variations, Proceedings of IAG Symposium No.116; ed: Rapp R., Cazenave A., Nerem S.; Springer, Berlin.Google Scholar
- Gruber Th., Anzenhofer M., Rentsch M., and Schwintzer P. (1997); Improvements in highresolution gravity field modelling at GFZ; this issue.Google Scholar
- Haxby W.F., Karner G.D., LaBrecque J.L., and Weissel J.K. (1983); Digital Images of Combined Oceanic and Continental Data Sets and Their Use in Tectonic Studies; EOS Transactions AGU 64, 995–1004.Google Scholar
- Hwang C. and Parsons B. (1996); An optimal procedure for deriving marine gravity frommulti-satellite altimetry; Geophysical Journal International 125, 705–718.Google Scholar
- Knudsen P. and Andersen O.B. (1997); New global gravity field from the ERS-1 GeodeticMission altimetry; this issue.Google Scholar
- Marks K.M., McAdoo D.C., and Smith W.H.F. (1993); Mapping the Southwest Indian Ridge with Geosat; EOS Transactions AGU 74, 81, 86, 87.Google Scholar
- Mazzega P., Berge M., Cazenave A., and Schaeffer P. (1997); Mean sea surface and gravity anomaly maps from multi-satellite altimetry; this issue.Google Scholar
- Neumann G.A., Forsyth D.W., and Sandwell D.T. (1993); Comparison of marine gravity from shipboard and high-density satellite altimetry along the Mid-Atlantic ridge, 30.5 ° 35.5°S; Geophysical Research Letters 20, 1639–1642.Google Scholar
- Olgiati A., Balmino G., Sarrailh M., and Green C.M. (1994); Gravity Anomalies From Satellite Altimetry; Bulletin Geodesique 69, 252–260.Google Scholar
- Rapp R.H. (1979); Geos 3 Data Processing for the Recovery of Geoid Undulations and Gravity Anomalies; Journal of Geophysical Research 84, 3784–3792.Google Scholar
- Sandwell D.T. (1992); Antarctic marine gravity field from high-density satellite altimetry; Geophysical Journal International 109, 437–448.Google Scholar
- Sarrailh M., Balmino G., and Doublet D. (1997); The artic ocean gravity field from ERS-1 altimetric data; this issue.Google Scholar
- Smith W.H.F. and Sandwell D.T. (1995); Marine gravity field from declassified Geosatand ERS-1 altimetry (Abstract); EOS Transactions AGU 76 (Supplement), G42A-02. SmithGoogle Scholar
- Smith W.H.F. and Sandwell D.T. (1997); Detailed gravity anomaly and predicted depthimages produced from combined ERS-1 and Geosat altimeter data; this issue.Google Scholar