Definitions

Bouguer, Pierre

Bouguer, Pierre, 1698-1758, French mathematician and hydrographer. He made some of the first photometric measurements, calculating the intensity of the light of the sun as compared with that of the moon, and invented (1748) the heliometer. His works include Essai d'optique sur la gradation de la lumière (1729) and La Figure de la terre (1749).
In geodesy and geophysics, the Bouguer anomaly (named after Pierre Bouguer) is computed from a free-air anomaly by computationally removing from it the attraction of the terrain, the Bouguer reduction.

In case where the effects of terrain are removed precisely, we speak of a refined or complete Bouguer reduction. In case the terrain is approximated by a flat plate of thickness $H$, the height of the gravity measurement location above sea level, we speak of a simple Bouguer reduction. The difference between the two, the differential gravitational effect of the unevenness of the terrain, is called the terrain effect. It is always negative.

The equation for the simple Bouguer reduction is δG_f = 2Hρπγ, where H is the thickness of the plate, γ is the constant of gravitation and ρ is the density of the material.