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 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. 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 theInternational Gravity Standardization Net 1971 (IGSN71). The deflections are referred to the Geodetic Reference System 1980 (GRS80) ellipsoidal normals. The deflections of the vertical incorporate the reference system relationship between NAD 83(86) and ITRF94(1996.0), the datum offset of NAVD 88, and thecontributions from 2951 GPS on leveled benchmarks. The curvature of the plumb line correction has been applied. http://www.ngs.noaa.gov/DEFLEC/deflec.html We are particularly grateful to NGA (former National Imagery and Mapping Agency) for their assistance and their data contributions.

A 1 kilometer Complete Bouguer Anomaly gravity grid of interior Alaska. Only those grid cells within 10 kilometers of a gravity data point have gravity values. Number of columns is 850 and number of rows is 600. The order of the data is from the lower left to the right and then up one row.

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 anomaly computation uses the Geodetic Reference System 1967 (GRS 67) theoretical gravity formula. Note that the original USGS Open File Report by D. F. Barnes mentions the use of the 1931 International Ellipsoid for gravity reduction but this is believed to have subsequently been changed to the GRS 67 system.

A 1 kilometer Complete Bouguer Anomaly gravity grid of interior Alaska. All grid cells within the rectangular data area (from 61 to 66 degrees North latitude and from 144 to 159 degrees West longitude) have interpolated data values. Number of columns is 850 and number of rows is 600. The order of the data is from the lower left to the right and then up one row.

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 anomaly computation uses the Geodetic Reference System 1967 (GRS 67) theoretical gravity formula. Note that the original USGS Open File Report by D. F. Barnes mentions the use of the 1931 International Ellipsoid for gravity reduction but this is believed to have subsequently been changed to the GRS 67 system.

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.

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. bounded by 61 to 66 degrees latitude and 144 to 159 degrees longitude in the interior of Alaska, In addition, the data has been gridded and maps have been recently published through the USGS, Map GP-1016.

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 topographic 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' 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.