|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.