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U.S. East-West Deflections (DEFLEC96)
This 2’ surface deflection of the vertical grid for the conterminous United States is the DEFLEC96 model. The computationused about 1.8 million terrestrial and marine gravity data held in the National Geodetic Survey gravity data base in July 1996. Thesedata were augmented by gravity data contributions from NGA (former National Imagery and Mapping Agency (former Defence Mapping Agency)). The deflections were obtained by numerical differentiation of cubic spline models along theparallels of the GEOID96 grid. The gravity values are based on the International Gravity Standardization Net 1971 (IGSN71). The deflections are referred to the Geodetic Reference System 1980 GRS80) ellipsoidal normals. The deflections of the verticalincorporate the reference system relationship between NAD 83(86)and ITRF94(1996.0), the datum offset of NAVD 88, and the contributions from 2951 GPS on leveled benchmarks. The curvatureof the plumb line correction has been applied. We are particularly grateful to NGA (former National Imagery and Mapping Agency) for their assistance and their data contributions.