In geodesy and geophysics, the Bouguer anomaly (named after Pierre Bouguer) is a gravity anomaly, corrected for the height at which it is measured and the attraction of terrain. The height correction alone gives a free-air gravity anomaly.

The Bouguer anomaly ${\displaystyle g_{B}}$ defined as:

$${\displaystyle g_{B}=g_{F}-\delta g_{B}+\delta g_{T}}$$

Here,

The free-air anomaly ${\displaystyle g_{F}}$, in its turn, is related to the observed gravity ${\displaystyle g_{obs}}$ as follows:

$${\displaystyle g_{F}=g_{obs}-g_{\lambda }+\delta g_{F}}$$

where:

A Bouguer reduction is called simple (or incomplete) if the terrain is approximated by an infinite flat plate called the Bouguer plate. A refined (or complete) Bouguer reduction removes the effects of terrain more precisely. The difference between the two is called the (residual) terrain effect (or (residual) terrain correction) and is due to the differential gravitational effect of the unevenness of the terrain; it is always negative.