A comparison of gravimetric techniques for measuring subsurface void signals

To demonstrate the potential of gravity gradiometry in the detection of underground structures or voids, an experiment was carried out at an underground missile launch facility at Vandenberg Air Force Base, California. Gravity data were collected using a LaCoste-Romberg Model G gravimeter and gravity gradient measurements were made using a vertical spin-axis Lockheed Martin developed arms control verification gravity gradiometer. After performing all necessary corrections, the data were compared to modelled signatures of the launch facility. Peak gravity and gravity gradient anomalies of approximately -75 mu Gal (1 mu Gal = 10(-8) m s(-1)) and 30 E(1 E = 10(-9) s(-2)) respectively were measured over the centreline of the largest capsule. The presence of the buried launch facility was apparent in both the observed gravity and gravity gradient data. The gravity gradients were unambiguous in resolving the underground facility's signature and thus revealing its location. In contrast, identifying the launch complex solely from the gravity anomaly data would have proven difficult due to a strong regional trend across the target area.