 Free-air gravity anomaly

gravity reduced to a reference elevation while retaining the gravitational contribution of the intervening topographic mass. The local elevation correction is approximately $2gh/R$ for a spherical reference, with sign chosen to undo the measured decrease with height.

The Free-Air Gravity Anomaly (FAGA) is a geophysical measurement that represents the difference between the observed gravity and the gravity value that would be expected at a particular elevation above a reference surface, typically the Earth's mean sea level. This measurement helps to identify variations in the Earth's gravitational field that are not due to changes in elevation, such as those caused by geological structures.