### Bouguer anomaly

(gravity's local variation after compensating for altitude and landforms)

In geophysics, including gravimetry, the term **Bouguer anomaly**
(or **Bouguer gravity anomaly**) is the gravity anomaly (of some
point on a planet) after compensating for altitude and for the
difference in mass underneath due to landforms (extra for a mountain,
less, for a valley). The gravity anomaly still present if an
adjustment is made only for altitude is termed the
free-air anomaly, and the
*Bouguer anomaly* additionally discounts the effect on gravity
due to the mass of the landform. Thus, if you are on top of
a mountain and measure a gravity anomaly, the free-air anomaly
is the reduced anomaly after you have taken into account how far
above sea level you are, and the Bouguer anomaly is what is left
of the anomaly after you have taken into account the density and
shape of the mountain beneath you. This remaining anomaly
is that due to other density variations beneath you within the
mountain or below it.
The compensation for these two effects is
termed the **Bouguer correction** or **Bouguer reduction**.
The term **Bouguer gravity** refers to the gravity
across the surface of the body after the Bouguer correction
has been applied. A **Bouguer gravity map** is a map of the
free-air gravity.

A simplified calculated Bouguer reduction, due essentially to the difference in
nearby mass given the vertical difference in ground height, is
termed the **simple Bouguer reduction** or **incomplete Bouguer reduction**,
while one that takes into account more terrain detail is called the
**refined Bouguer reduction** or **complete Bouguer reduction**.

(*geophysics,gravity*)
**Further reading:**

http://en.wikipedia.org/wiki/Bouguer_anomaly

**Referenced by pages:**

free-air anomaly

gravity anomaly

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