REGIONAL RECOVERY OF THE GRAVITY-FIELD FROM SATELLITE GRAVITY GRADIOMETER AND GRAVITY VECTOR DATA USING COLLOCATION

The method of least squares collocation has been used to investigate t he regional recovery of the gravity field from satellite gravity gradi ometer (SGG) data and gravity vector data derived from, e.g., satellit e-to-satellite tracking (SST). We chose a region centered over the Eur opean Alps where the gravity anomalies showed a (large) standard devia tion of 60 mGal. Mean gravity anomalies were used to generate SGG data at a satellite altitude of 200 km. As SGG data we used the second-ord er derivatives in radial direction, across-track, and the mixed radial /cross-track derivative, all assumed to have an associated noise equal to 0.01 EU (Eotvos unit =EU, 1 EU=10(-9)s(-2)). As gravity data we us ed the three components of the gravity vector, assuming that the assoc iated errors were uncorrelated noise with standard deviation equal to 1 mGal, The satellite data in the test area were used in combination t o predict 0:5(0) mean gravity anomalies and geoid heights. Ground trut h data were used to investigate the quality of the recovery. The diffe rence between observed and computed values have a standard deviation e qual to 22 mGal in the best case, The use of the gravity vector data g ave no improvement when added to the SGG data. The use of topographic information with 5 are min resolution (ETOPO5U) gave, after removal of severe errors, a 17-mGal standard deviation of observed minus compute d values. This is a much smaller improvement than expected but is due to errors in the:topographic values.