This 2' gravity density grid for the conterminous United States displays the distribution of the 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)) 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' 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.

This 2' gravity density grid for Mexico, North-Central America, and the Western Caribbean Sea shows the distribution of about one million terrestrial and marine gravity measurements held in the NGS database as of March 1997. These gravity measurements have been augmented by data contributions from NGA (former National Imagery and Mapping Agency), and satellite altimeter-derived gravity anomalies computed by Sandwell and Smith (1997). This density grid shows the number of gravity data contained in a 2' x 2' cell. Please note that this coverage grid does not show the 15'x15' EGM96 gravity values used to fill the void areas south of 20 degrees North. Additional information is available at: http://www.ngs.noaa.gov/GEOID/MEXICO97 .We are particularly grateful to NGA (former National Imagery and Mapping Agency) for their assistance and their data contributions.

This 2' geoid height grid for Puerto Rico and the Virgin Islands is distributed as a GEOID96 model. The computation used 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)). 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.htmlWe are particularly grateful to NGA (former National Imagery and Mapping Agency) for their assistance and their data contributions.

The gravity station data (1,522 records) were compiled by the Portland State University. This data base was received in August 1990. Principal gravity parameters include Free-air Anomalies and Complete Bouguer Anomalies (terrain correction applied). 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 the greater Portland area.

GEOSAT DATA: Gridded Gravity Anomalies for the Southern Ocean

GEOSAT DATA: Gridded Gravity Anomalies for the Southern Ocean

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 gravity station data (152,624 records) were compiled by the University of Texas at Dallas. This data base was received in June 1992. Principal gravity parameters include Free-air Anomalies and Simple Bouguer Anomalies (no terrain correction applied). 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 and offshore of South America.

The gravity station data (55,907 records) were gathered by various governmental organizations (and academia) using a variety of methods. This data base was received in March 1993. Principal gravity parameters include Free-air Anomalies and Simple Bouguer Anomalies (no terrain correction applied). The observed gravity values are referenced to the International Gravity Standardization Net 1971 (IGSN 71) and the gravity anomaly computation uses the Geodetic Reference System 1967 (GRS 67) theoretical gravity formula. The spatial resolution of the data is randomly distributed within the boundaries of Minnesota.

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. The data are randomly distributed within the area bounded by 64 - 71 degrees West and 20 - 29 degrees South in the Central Andes of South America.