Free-air Gravity Anomaly - Anomaly

Anomaly

The free-air gravity anomaly is given by the equation:

Here, is the free-air gravity anomaly, is observed gravity, is the correction for latitude (because the Earth is not a perfect sphere), and is the free-air correction.

Gravitational acceleration decreases as an inverse square law with the distance at which the measurement is made from the mass. The free air correction is calculated from Newton's Law, as a rate of change of gravity with distance:

At the equator, mGal/m.

The difference between gravity measurements at sea level and at an altitude of above sea level is:

.

Here we have assumed that measurements are made relatively close to the earth's surface so that R doesn't vary significantly. Also, there is an assumption that no mass exists between the observation point and sea level. The Bouguer anomaly and terrain correction are used to account for this.