GLOBAL MARINE GRAVITY-FIELD FROM THE ERS-1 AND GEOSAT GEODETIC MISSION ALTIMETRY

Satellite altimetry from the Geosat and the ERS-1 Geodetic Missions pr ovide altimeter data with very dense spatial coverage. Therefore the g ravity field may be recovered in great detail. As neighboring ground t racks are very closely distributed, cross-track variations in the sea surface heights are extremely sensitive to sea surface variability. To avoid errors in the gravity field caused by such effects, sea surface variability needs to be carefully eliminated from the observations. I nitially, a careful removal of gross errors and outliers was performed , and the tracks were fitted individually to a geoid model and crossov er adjusted using bias and tilt. Subsequently, sea surface heights wer e gridded using local collocation in which residual ocean variability was considered. The conversion of the heights into gravity anomalies w as carried out using the fast Fourier transform (FFT). In this process , filtering was done in the spectral domain to avoid the so-called ''o range skin'' characteristics. Comparison with marine gravity was final ly carried out in three different regions of the Earth to evaluate the accuracy of the global marine gravity field from ERS-1 and Geosat.