On The Range Of Investigation Of A Borehole Gravimeter

Concepts of the range of investigation of a borehole gravimeter are reviewed. It is shown that the maximum sensitivity to a mass point at a horizontal distance R from a borehole occurs at a vertical distance Z = R/sqrt 2. Thus, the angle of maximum sensitivity is about 55" from the vertical. It is also shown that the absolute value of the gravitational effect decreases with increasing R. There are two maxima of the vertical gradient of gravity(at Z = 0 and at Z = sqrt(3/2) R). The minimum distance required between gravimeter stations to obtain a usable measurement can be determined. The slab radius R for which the gravitational effect of a horizontal slab is equal to 45%, 90%, etc., of that of an infinite horizontal slab is a function of the measurement spacing. The closer the measurement spacing, the more information obtained.