This 2? geoid height grid for Puerto Rico and the Virgin Islands is distributed as
a GEOID96 model. The computation used 26,000 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. Unlike the grid for the conterminous United
States, this GEOID96 grid does not incorporate GPS on leveled benchmarks. This model
is a gravimetric geoid in a geocentric, ITRF94(1996.0) reference frame. It is necessary
to subtract 12.0 cm from these values to obtain the geoid undulation between the best-fit
global geopotential surface and the GRS80 ellipsoid (both expressed in a tide free
system). Additional information is available at: http://www.ngs.noaa.gov/GEOID/geoid.htmlWe
are particularly grateful to NGA (former National Imagery and Mapping Agency) for
their assistance and their data contributions. |