|U.S. North-South 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.
These data 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 the meridians of
the GEOID96 grid. The gravity values are based on theInternational Gravity Standardization
Net 1971 (IGSN71). The deflections are referred to the Geodetic Reference System 1980
(GRS80) ellipsoidal normals. The deflections of the vertical incorporate the reference
system relationship between NAD 83(86) and ITRF94(1996.0), the datum offset of NAVD
88, and thecontributions from 2951 GPS on leveled benchmarks. The curvature of the
plumb line correction has been applied. http://www.ngs.noaa.gov/DEFLEC/deflec.html
We are particularly grateful to NGA (former National Imagery and Mapping Agency) for
their assistance and their data contributions.