Increased resolution of processed satellite altimeter data: The development of a quality global gravity database

Abstract

Global coverage of satellite altimeter missions have been steadily increasing with the advent of new missions. In particular, the Geosat mission has provided the greatest advance, both because of the close track spacings of the Geodetic Mission and the 68 fold redundancy of tracks from the Exact Repeat Mission. It is this redundancy which allows "stacking" of the track data to yield a superior horizontal resolution and accuracy. Processing of the repeat tracks must involve many considerations to yield the optimum resolution, both with respect to atmospheric and altimeter orbit considerations. Recent improvements in the binning and gridding algorithms in particular have allowed the data to be gridded into 1/20° bins, using the 10 Hz data resampled to 5 Hz. Integrated gridding of all available mission data has now allowed the compilation of a global gravity grid with an accuracy of less than 1 mGal, and a cross-track resolution of the order of 19 km north of 30°S, and 14 km south of 30°S. Further missions, both those presently acquiring data and those planned for the future will be similarly processed using the concepts developed for the Geosat data. Continuing incorporation of these data will continue to improve the resolution of the data. Furthermore, the extremely high accuracy of these new missions will help to redefine the global geoid models, allowing the improved removal of spurious factors such as dynamic topography. A global gravity database now exists for all oceanic areas, providing a resolution and accuracy often comparable to shipborne gravity, available at a fraction of the cost.