A comparison of gravimetric techniques for measuringsubsurface void signals

Abstract

To demonstrate the potential of gravity gradiometry in thedetection of underground structures or voids, an experiment was carriedout at an underground missile launch facility at Vandenberg Air ForceBase, California. Gravity data were collected using a LaCoste-RombergModel G gravimeter and gravity gradient measurements were made using avertical spin-axis Lockheed Martin developed arms control verificationgravity gradiometer. After performing all necessary corrections, the datawere compared to modelled signatures of the launch facility. Peak gravityand gravity gradient anomalies of approximately -75 µGal (1 µGal = 10-8 m s-1) and 30 E (1 E = 10-9 s-2) respectivelywere measured over the centreline of the largest capsule. The presence ofthe buried launch facility was apparent in both the observed gravity andgravity gradient data. The gravity gradients were unambiguous in resolvingthe underground facility's signature and thus revealing its location. Incontrast, identifying the launch complex solely from the gravity anomalydata would have proven difficult due to a strong regional trend across thetarget area.}\\fnm{4}{National Imagery and Mapping Agency, Patrick AFB,FL 32925-3438, USA.}\\fnm{5}{MITRE Corporation, Bedford, Massachusetts 01730-1420, USA.