This 2' surface deflection of the vertical grid for the conterminous United States is the DEFLEC96 model. The computationused about 1.8 million terrestrial and marine gravity data held in the National Geodetic Survey gravity data base in July 1996. Thesedata were augmented by gravity data 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 theparallels 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 deflections of the verticalincorporate the reference system relationship between NAD 83(86)and ITRF94(1996.0), the datum offset of NAVD 88, and the contributions from 2951 GPS on leveled benchmarks. The curvatureof 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' surface deflection of the vertical grid for Puerto Rico and the Virgin Islands is distributed as the DEFLEC96 model. The computation used about 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)). The deflections were obtained by numerical differentiation of cubic spline models along the meridians of the GEOID96 grid. The gravity values are based on the International Gravity Standardization Net 1971IGSN71). The deflections are referred to theGeodetic Reference System 1980 (GRS80) ellipsoidal normals. The curvature of the plumbline correction has been applied. We are particularly grateful to NGA (former National Imagery and Mapping Agency) for theirassistance and their data contributions.

This 2' x 4' surface deflection of the vertical grid for Alaska is the DEFLEC96 model. The computation used 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 DefenseMapping Agency). The deflections were obtained by numerical differentiation of cubic spline models along the meridians 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.Additional information is available at:http://www.ngs.noaa.gov/ We are particularlygrateful to NGA (former National Imagery and Mapping Agency) for their assistance and their data contributions.

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' surface deflection of the vertical grid for Mexico, and North-Central is the DMEX97 model. The computation used about one million terrestrial and marine gravity measurements heldin the NGS database as of March 1997. These gravity measurements were augmented by data contributions from NGA (former National Imagery and Mapping Agency), and satellitealtimeter derived gravity anomalies computed by Sandwell and Smith (1997). The deflection values themselves were obtained by numerical differentiation of cubic spline models along the meridians of the MEXICO97 geoid grid, followed by a correction for curvature of the plumb line, yielding surface deflections of the vertical. Since the EGM96 model was used to fill data gaps south of 20 degrees North latitude, the deflections in and around those regions will be less accurate. The gravity values are based on the International Gravity Standardization Net 1971 (IGSN71). The deflections are referred to Geodetic Reference System 1980 (GRS80) ellipsoidal normals oriented in the International Terrestrial Reference Frame 1994 (ITRF94(1996.0)). We are particularly grateful to NGA (former National Imagery and Mapping Agency) for their assistance and their data contributions.

This 2' surface deflection of the vertical grid for Puerto Rico and the Virgin Islands is distributed as the DEFLEC96 model. The computation used about 26,000 terrestrial and marine gravity data held in the National Geodetic Survey gravity data base in July 1996. These data were augmented bygravity data contributions from NGA (former National Imagery and Mapping Agency) (formerDefense Mapping Agency).The deflections wereobtained by numerical differentiation of cubicspline models along the parallels of the GEOID96grid. The gravity values are based on theInternational Gravity Standardization Net 1971IGSN71). The deflections are referred to in theGeodetic Reference System 1980 (GRS80)ellipsoidal normals. The curvature of the plumbline correction has been applied. We areparticularly grateful to NGA (former National Imagery and Mapping Agency) for theirassistance 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.

isotop.bin - topographic data for conterminous U.S. projected on an 8 km grid. Projection is Albers, central meridian = 96 degrees West, base latitude = 0 degrees North. Elevations are in meters.

A 2.5 kilometer Bouguer anomaly grid for the state of Utah. Number of columns is 196 and number of rows is 245. The order of the data is from the lower left to the right and then up one row.

This 2' geoid height grid for the conterminous United States is the GEOID96 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. GEOID96 incorporates the reference system relationship between NAD 83(86) and ITRF94(1996.0), the datum offset of NAVD 88, and the contributions from 2951 GPS on leveled benchmarks. 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.