Improved Recovery of Gravity Anomalies from Dense Altimeter Data
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Date
1996-02
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Ohio State University. Division of Geodetic Science
Abstract
A procedure is developed to recover sea surface heights (SSH) and free-air (FA) gravity anomalies from dense satellite altimeter SSH data with enhanced accuracies over the full spectrum of the gravity field for geological exploration of the sea floor. A key element of the procedure is wavenumber correlation filtering (WCF) of co-linear SSH tracks for the coherent signals of subsurface geological masses. Orbital cross-over adjustments with bias parameters are applied to the filtered SSH data, which are then separated into two groups of ascending and descending tracks and gridded with tensioned splines. A directional sensitive filter (DSF) is developed and applied to reduce residual errors in the orbital adjustments that appear as track patterned SSH. Subtracting sea surface topography from the SSH yields a high resolution estimate of geoid undulations from which FA gravity anomalies can be obtained by the application of a gradient filter. These procedure are applied to the Geosat Geodetic Mission (GM) data of the southern oceans in a test area of ca. 900 km x 1,200 km to resolve geoid undulations and FA gravity anomalies to wavelengths of ~10 km and larger. Comparisons with gravity data from ship surveys, predictions by least squares collocation (LSC), and 2 versions of NOAA's predictions using vertical deflections illustrate the performance of this procedure for recovering all elements of the gravity spectrum. Statistics on differences between precise ship data and predicted FA gravity anomalies show a mean of 0.1 mgal, an RMS of 3.5 mgal, maximum differences of 10.2 mgal and -18.6 mgal, and a correlation coefficient of 0.993 over four straight ship tracks of ca. 1,600 km where gravity changes over 150 mgals.