Physical Geodesy - Gravity Anomalies

Above we already made use of gravity anomalies . These are computed as the differences between true (observed) gravity, and calculated (normal) gravity . (This is an oversimplification; in practice the location in space at which γ is evaluated will differ slightly from that where g has been measured.) We thus get

$\Delta g = g - \gamma.\,$

These anomalies are called free-air anomalies, and are the ones to be used in the above Stokes equation.

In geophysics, these anomalies are often further reduced by removing from them the attraction of the topography, which for a flat, horizontal plate (Bouguer plate) of thickness H is given by

$a_B=2\pi G\rho H,\,$

The Bouguer reduction to be applied as follows:

$\Delta g_B = \Delta g_{FA} - a_B,\,$

so-called Bouguer anomalies. Here, is our earlier, the free-air anomaly.

In case the terrain is not a flat plate (the usual case!) we use for H the local terrain height value but apply a further correction called the terrain correction (TC).

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