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U.S. Terrain Corrected Free Air Anomalies (96)
This 2’ gravity anomaly grid for the conterminous United States is NOT the input data set used in development of the GEOID96 model. This gravity grid models the 1.7 million terrestrial and marine gravity data held in the National Geodetic Survey gravity data base in July 1996. The data used in this grid have NOT been augmented by gravity data contributions from NGA (former National Imagery and Mapping Agency (former Defence Mapping Agency)). Please note that the GEOID96 model itself does contain the NGA (former National Imagery and Mapping Agency) contributions. These gravity values are based on the International Gravity Standardization Net 1971 (IGSN71). Terrain corrected, atmospherically corrected, Bouguer anomalies were computed with respect to the Geodetic Reference System 1980 (GRS80) using NAD83 and NAVD88 coordinates. Terrain corrections were computed by FFT integration of 30" digital elevation data throughout the United States. These complete Bouguer anomalies were gridded by splines in tension. The free air anomaly grid was obtained by restoring the Bouguer plate with a 2’ mean elevation grid. Additional information is available at http://www.ngs.noaa.gov/GEOID/geoid.html