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Earth Gravity Model.
The official Earth Gravitational Model EGM2008 has been publicly released by the National GeospatialIntelligence Agency (NGA) EGM Development Team. This gravitational model is complete to spherical harmonic degree and order 2159, and contains additional coefficients extending to degree 2190 and order 2159. Full access to the model's coefficients and other descriptive files with additional details about EGM2008 are provided within these web pages.

Gravity Anomalies.
A gravity anomaly is the difference between the observed acceleration of Earth's gravity and a value predicted from a model. The subtle difference between gravity anomalies and gravity disturbances has lead to conflicting definitions of what a gravity anomaly actually is.
The gravity anomaly is typically defined in one of two ways:
 The difference between gravity on the geoid and gravity on the reference spheroid (mostly in geodesy);
 The difference between observed gravity and some theoretical value of gravity predicted at the measurement point (mostly in geophysics).



