The delineation and interpretation of the Earth's gravity field

The observed changes in velocity with time are reduced relative to the well-determined low degree and order GEM field model and accelerations are found by analytical differentiation of the range rates. This new map is essentially identical to the first map and we have produced a composite map by combining all 90 passes of SST data. The resolution of the map is at worst about 5 deg and much better in most places. A comparison of this map with conventional GEM models shows very good agreement. A reduction of the SEASAT altimeter data has also been carried out for an additional comparison. Although the SEASAT geoid contains much more high frequency information, it agrees very well with both the SST and GEM fields. The maps are dominated (especially in the east) by a pattern of roughly east-west anomalies with a transverse wavelength of about 2000 km. A further comparison with regional bathymetric data shows a remarkably close correlation with plate age.