The location of subterranean voids using tensor gravity gradiometry

This paper discusses the use of signals from tensor gravity gradiometers to target compact, local, subterranean voids. Two generic types of gravitational source are analysed in detail, and compared: a cubical subterranean void, and a subterranean tunnel. A vectorial targeting method is shown to work well with both types of finite target, picking out the centre of mass of the cubical source, and the axis of the tunnel. Some unusual results are reported in connection with the apparent length of the tunnel target, and limitations on the information that may be gleaned from the gravity gradient signals arising from both types of target are discussed.