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 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 GEOID96, the G96SSS grid does not incorporate GPS on leveled benchmarks. The G96SSS model is a gravimetric geoid in a geocentric, ITRF94(1996.0) reference frame. It is necessary to subtract 12.0 cm from the G96SSS 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 We are particularly grateful to NGA (former National Imagery and Mapping Agency) for their assistance and their data contributions.

The gravity station data (1294 records) were compiled by the Alaska Geological Survey and the U.S. Geological Survey, Menlo Park, California. This data base was received in September 1986. Principal gravity parameters include Free-air Anomalies and Simple Bouguer Anomalies (no terrain correction applied) and altimeter elevations to compute the anomalies. The observed gravity values are referenced to the International Gravity Standardization Net 1971 (IGSN 71). The gravity anomaly computation uses the Geodetic Reference System 1967 (GRS 67) theoretical gravity formula. The data are randomly distributed within the boundaries of central Alaska.

This 2' x 4' surface deflection of the vertical grid for Alaska is the DEFLEC96 model. The computation used about 1.1 millionterrestrial and marine gravity data held in the National Geodetic Survey gravity data base in July 1996. These data were augmented by gravitydata contributions from NGA (former National Imagery and Mapping Agency (former Defence Mapping Agency)). The deflections were obtained by numerical differentiation of cubic spline models along the parallels of the GEOID96 grid. The gravity values are based on the International Gravity Standardization Net 1971 (IGSN71).The deflections are referred to the Geodetic Reference System 1980 (GRS80) ellipsoidal normals. The curvature of the plumb line correction has been applied. We are particularly grateful to NGA (former National Imagery and Mapping Agency) for their assistance and their data contributions.

This 2' x 4' gravity density grid for Alaska displays the distribution of about 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)) and by satellite altimeter-derived marine gravity anomalies computed by Sandwell and Smith (1996). The values show the number of gravity data contained in a given 2' x 4' cell. 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.

The Decade of North American Geology (DNAG) gravity grid values, spaced at 6 km, were used to produce the Gravity Anomaly Map of North America (1987; scale 1:5,000,000). Considerable caution should be exercised when using these gridded data in regions of sparse coverage (for example, deep oceanic areas). The spatial distribution of the original data from which the grid was generated is shown on sheet 5 of the published map. Note: There are no gridded data values for Mexico.

A 2 kilometer terrace-density grid for the Idaho batholith study area. Number of columns is 331 and number of rows is 285. The order of the data is from the lower left to the right and then up one row.

These grid files were used to produce gravity and basin depth maps of the Basin and Range Province, western United States. The maps show gravity values and modeled basin depths in this area. The data were compiled by the U.S. Geological Survey, Denver, Colorado. This data base was received in June, 1995. For further information see the readme.txt file in this directory(data\grids\basinrng), and the "Gravity and Basin-Depth Maps of the Basin and Range Province, Western United States", by R.W. Saltus and R.C. Jachens, Map GP-1012.

The gravity station data (24,284 records) were compiled by the U. S. Geological Survey. This data base was received on February 23, 1993. Principal gravity parameters include observed gravity, Free-air anomalies and Bouguer anomalies. The observed gravity values are referenced to the International Gravity Standardization Net 1971 (IGSN 71). The gravity anomaly computation uses the Geodetic Reference System 1967 (GRS 67) theoretical gravity formula.

These grid files were used to produce gravity and basin depth maps of the Basin and Range Province, western United States. The maps show gravity values and modeled basin depths in this area. The data were compiled by the U.S. Geological Survey, Denver, Colorado. This data base was received in June, 1995. For further information see the readme.txt file in this directory(data\grids\basinrng), and the "Gravity and Basin-Depth Maps of the Basin and Range Province, Western United States", by R.W. Saltus and R.C. Jachens, Map GP-1012.

These grid files were used to produce gravity and basin depth maps of the Basin and Range Province, western United States. The maps show gravity values and modeled basin depths in this area. The data were compiled by the U.S. Geological Survey, Denver, Colorado. This data base was received in June, 1995. For further information see the readme.txt file in this directory (data\grids\basinrng), and the "Gravity and Basin-Depth Maps of the Basin and Range Province, Western United States", by R.W. Saltus and R.C. Jachens, Map GP-1012.