A comparison of gravimetric techniques for measuring subsurface void signals

To demonstrate the potential of gravity gradiometry in the detection of und erground structures or voids, an experiment was carried out at an undergrou nd missile launch facility at Vandenberg Air Force Base, California. Gravit y data were collected using a LaCoste-Romberg Model G gravimeter and gravit y gradient measurements were made using a vertical spin-axis Lockheed Marti n developed arms control verification gravity gradiometer. After performing all necessary corrections, the data were compared to modelled signatures o f the launch facility. Peak gravity and gravity gradient anomalies of appro ximately -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. Th e presence of the buried launch facility was apparent in both the observed gravity and gravity gradient data. The gravity gradients were unambiguous i n resolving the underground facility's signature and thus revealing its loc ation. In contrast, identifying the launch complex solely from the gravity anomaly data would have proven difficult due to a strong regional trend acr oss the target area.