Alaska Geoid Heights (GEOID96) |
This 2? x 4? geoid height grid for Alaska is distributed as a GEOID96 model. The computation
used 1.1 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. 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.html We are particularly
grateful to NGA (former National Imagery and Mapping Agency) for their assistance
and their data contributions. |
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