This 2' geoid height grid for the conterminous United States is the G96SSS 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 2.5-min isostatic gravity data set was produced by regridding the 4-km residual isostatic gravity grid of the U.S. The isostatic residual gravity grid was developed by the U.S. Geological Survey using an Airy Heiskanen model. Local compensation was computed with a depth of 30.0 km to the root for sites with sea level elevations and a density contrast of 0.35 g/cm3 across the bottom of the root.

The high density Geosat/GM altimeter data south of 30 S have finally arrived. In addition, ERS-1 has completed more than 6 cycles of its 35-day repeat track. These data provide a dramatically improved view of the marine gravity field.

The NGS Absolute Gravity data (78 stations) was received in July 1993. Principal gravity parameters include Gravity Value, Uncertainty, and Vertical Gradient. The data are randomly spaced worldwide.

The gravity network data (7,298 records) were gathered by various governmental organizations (and academia) using a variety of methods.

This data base (14,559 records) was received in January 1986. Principal gravity parameters include elevation and observed gravity. The observed gravity values are referenced to the International Gravity Standardization Net 1971 (IGSN 71). The data are randomly distributed within the boundaries of the Republic of South Africa.

The gravity station data (72,677 records) were compiled by the U.S. Geological Survey and the State of Alaska Division of Geological & Geophysical Surveys. This data base was received in February, 1993. Principal gravity parameters include Free-air anomalies, isostatic anomalies and Simple Bouguer anomalies (no terrain correction applied). The "iso" suffix indicates that a crustal thickness of 25 kilometers was used in the isostatic calculation. The observed gravity values are referenced to the International Gravity Standardization Net 1971 (IGSN 71).

The gravity station data (10,578 records) were compiled by the U.S. Geological Survey and the State of Alaska Division of Geological & Geophysical Surveys. This data base was received in February, 1993. Principal gravity parameters include Free-air anomalies, isostatic anomalies and Simple Bouguer anomalies (no terrain correction applied). The "wpn" suffix indicates that a crustal thickness of 30 kilometers was used in the isostatic calculation. The observed gravity values are referenced to the International Gravity Standardization Net 1971 (IGSN 71).

The gravity station data total 9416 records. This data base was received in March 1997. Principal gravity parameters include Free-air Anomalies which have been adjusted to the International Gravity Standardization Net 1971 (IGSN 71). The gravity anomaly computation uses the Geodetic Reference System 1967 (GRS67) theoretical gravity formula. The data are randomly distributed within the area approx.

The Central Andes gravity data (6,151 records) were compiled by Professor Gotze and the MIGRA Group. This data base was received in April, 1997. Principal gravity parameters include Free-air Anomalies and Bouguer Anomalies (terrain and mass corrected). The gravity station data have been adjusted to the International Gravity Standardization Net 1971 (IGSN 71). The gravity anomaly computation uses the Geodetic Reference System 1967 (GRS 67) theoretical gravity formula.