|U.S. Geoid Heights (GEOID96)
|This 2’ geoid height grid for the conterminous United States is the GEOID96 model.
The computation used 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)). By means of a Fast Fourier Transform (FFT) technique,
high frequency corrections were made to an underlying EGM96 geopotential model through
a remove, compute, and restore process. The gravity values are based on the International
Gravity Standardization Net 1971 (IGSN71). The geoid heights are referred to the Geodetic
Reference System 1980 (GRS80) ellipsoid. GEOID96 incorporates 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. Additional information is available
at http://www.ngs.noaa.gov/GEOID/We are particularly grateful to NGA (former National
Imagery and Mapping Agency) for their assistance and their data contributions.