|Alaska Terrain Corrected Free Air Anomalies (96)
|This 2’ x 4’ gravity anomaly grid for Alaska is NOT the input data set used in development
of the GEOID96 model. This gravity grid models the 1.1 million terrestrial and marine
gravity data held in the National Geodetic Survey gravity data base in July 1996.
The data used in this grid have NOT been augmented by gravity data contributions from
NGA (former National Imagery and Mapping Agency (former Defence Mapping Agency)).
Please note that the GEOID96 model itself does contain the NGA (former National Imagery
and Mapping Agency) contributions. These gravity values are based on the International
Gravity Standardization Net 1971 (IGSN71). Terrain corrected, atmospherically corrected,
Bouguer anomalies were computed with respect to the Geodetic Reference System 1980
(GRS80) using NAD83 and NAVD88 coordinates. Terrain corrections were computed by an
FFT method from 30" x 60" digital elevation data. These complete Bouguer anomalies
were gridded by splines in tension. The free air anomaly grid was obtained by restoring
the Bouguer plate with a 2’ x 4’ mean elevation grid. Additional information is available