Bouguer Anomaly

The Bouguer anomaly is a minor variation in gravitational force equal to ± 300 milligals. (One milligal is equal to .001 galileos, a unit of acceleration equal to 1 cm/sec²). These variations in gravity occurr due to differences in the density of the rock that is underneath a certain location. This was first discovered by Pierre Bouguer from research conducted in the Andes.

The anomaly in gravity is calculated with the following formula:

Bouguer Anomaly = Gravity _measured + Free Air Correction - Bouguer Correction - Gravity _theoretical

Gravity _measured is a value that is measured with a gravitometer.

Free Air Correction is equal to ((2) (g_o) (h_e)) / R
Where g_o is equal to 980.000 gals
And h_e is the height above mean sea level at which you are taking measurements
And R is equal to the distance from the center of the earth to mean sea level. (6.37 x 10 ⁶ meters)

Bouguer Correction is equal to ((2) (π) (G) (ρ) (h _rock))
Where G is Cavendigh's Constant, 6.67 x 10 -8 (dyne cm²) / g²
And ρ is the density of the rocks below the area being measured
And h _rock is the distance from the base of the rock that makes up the area (the root of a mountain, for example) to the top of the rock that makes up the area.

Gravity _theoretical is calculated with a different formula, based on lattitude (represented by φ. This formula is:

978.049 ( 1 + .005288 sin²φ - .0000059 sin²2φ) galileos.

It is worth noting that there are some descrepancies that can be found in calculating this. I have also seen different numbers for various parts of the formula. I have seen the free air constant listed as 0.3086 mgal/m, and the Bouguer correction listed as 0.4185 <ρ> h, where h is = to h_e from above, in the free air correction. I have also seen a slightly different formula for the theoretical gravity, in which .0000059 sin⁴φ. If someone knows for certain exactly which ones of these things are correct, please /msg me, and I will change it.