GRAVITY-ANOMALIES FROM SATELLITE ALTIMETRY - COMPARISON BETWEEN COMPUTATION VIA GEOID HEIGHTS AND VIA DEFLECTIONS OF THE VERTICAL

The accumulation of good quality satellite altimetry missions allows us to have a precise geoid with fair resolution and to compute free air gravity anomalies easily by fast Fourier transform (FFT) techniques. In this study we are comparing two methods to get gravity anomalies. The first one is to establish a geoid grid and transform it into anomalies using inverse Stokes formula in the spectral domain via FFT. The second one computes deflection of the vertical grids and transforms them into anomalies. The comparison is made using different data sets: Geosat, ERS-1 and Topex-Poseidon exact repeat misions (ERMs) north of 30 degrees S and Geosat geodetic mission (GM) south of 30 degrees S. The second method which transforms the geoid gradients converted into deflection of the vertical values is much better and the results have been favourably evaluated by comparison with marine gravity data.