BGI > Data / Products > Grids and models > EGM2008 global model

View and extract regional grids from EGM2008

This page allows you to view and download regional gravity anomaly grids derived from the Earth Gravitational Model (EGM2008) released by the National Geospatial-Intelligence Agency (NGA) - See References.

Select a given area

Regional grids (averaged over 2,5 arc-minute by 2,5 arc-minute) will be derived from the EGM2008 model (extraction limited to 100°x100°)

GUINEA_BGI_EXTRACT_EGM08_JPEG_large

5'x5' free air anomaly grid

Ascii grid (Zip file) available on request.

AFRICA_BGI_EGM08_EXTRACT_5MIN_JPEG_large
SAMERICA_BGI_EGM08_EXTRACT_5MIN_JPEG_large

Anomaly computation

The regional Free-air and Bouguer gravity anomaly grids (averaged over 2,5 arc-minute by 2,5 arc-minute) are computed at BGI from the EGM2008 spherical harmonic coefficients (Pavlis et al., 2008). The Bouguer corrections computed at regional scales are obtained using the FA2BOUG code developed by Fullea et al. (2008). The topographic correction is applied up to a distance of 167 km using the 1 arc-minute by 1 arc-minute ETOPO1 Digital Elevation Model. Density reduction for Bouguer anomaly : 2,67.

  • Fullea, J., Fernandez, M., Zeyen, H., 2008. “FA2BOUG - A FORTRAN 90 code to compute Bouguer gravity anomalies from gridded free-air anomalies: Application to the Atlantic-Mediterranean transition zone”.Computers & Geosciences, Volume 34, Issue 12 (December 2008) pp. 1665-1681, ISSN:0098-3004. DOI: 10.1016/j.cageo.2008.02.018

A gravity anomaly is defined as the difference of actual (observed) gravity from a nominal (theoretical) value determined for an Earth model. The unit is “milliGal” (denoted mGal, where 1 mGal = 10-5 ms-2).

About EGM2008

The official Earth Gravitational Model EGM2008 has been publicly released by the National Geospatial-Intelligence Agency (NGA) EGM Development Team (N. K. Pavlis, S. A. Holmes, S. C. Kenyon and J. K. Factor. “An Earth Gravitational Model to Degree 2160: EGM2008”. EGU General Assembly 2008, Vienna, Austria, April 13-18, 2008). This gravitational model is complete to spherical harmonic degree and order 2159, and contains additional coefficients extending to degree 2190 and order 2159.

For more information, visit the EGM2008 webpage at the following link (NGA website):
http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm2008

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