Directory Title: U.S. Geoid Heights (GEOID96)
Principal Investigator: Dr. Dennis G. Milbert
Contributing Organization: NOAA, National Geodetic Survey, N/NGS5
                           1315 East-West Highway, Room 9349
                           Silver Spring, MD 20910-3282
                           dennis@ngs.noaa.gov

Summary:  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 NIMA (former Defense 
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/geoid.html
We are particularly grateful to NIMA for their assistance and their 
data contributions.