As the spacecraft orbits the earth it collects a continuous profile of geoid height across an ocean basin. Profiles from many satellites, collected over many years, are combined to make high resolution images. The Poster shows gravity anomaly derived from geoid height measurements from 4.5 years of Geosat measurements and 2 years of ERS-1 measurements. We have developed a new method to convert these raw geoid height measurements, which have a variety of accuracies, track spacings and data densities, into images (or grids) of gravity anomaly. This conversion is done to enhance the small-scale features of the seafloor. Moreover, after the conversion, the satellite-derived gravity measurements can be compared and combined with gravity anomaly measurements made by ships. The algorithms of the conversion are based on laws of physics, geometry and statistics. Since the data sets are large, diverse, and contaminated with errors, many sophisticated computer operations are required. The ultimate test of the accuracy of our methods is through comparisons with shipboard gravity measurements. Our latest grids show agreement with ship data at a level of 5 milligal (mgal). One mgal is about one millionth the normal pull of gravity (9.8 m/s2). Typical variations in the pull of gravity are 20 milligal although over the deep ocean trenches they exceed 300 mgal.
Information provided by: http://www.ngdc.noaa.gov