We tested Newton's inverse-square law of gravitation by comparing gravity measured on a 600-m tower with gravity calculated from ground measurements. A significant departure from the law was detected, approaching (-500 ±35)xlO~^ms~^at the top of the tower and suggestive of a rapidly attenuating non-Newtonian attractive force. These results are marginally consistent with a one-term Yukawa-type attractive force, but they are fully consistent with two Yukawa-type forces, attractive and repulsive, and then also with Airy and Cavendish experiments.
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 µGal (1 µGal = 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.} \fnm{4}{National Imagery and Mapping Agency, Patrick AFB, FL 32925-3438, USA.} \fnm{5}{MITRE Corporation, Bedford, Massachusetts 01730-1420, USA.
An experiment was performed to test Newton's inverse square law of gravitation. The test compared accurately measured gravity values along a 600‐m tower with upward continued gravity estimates calculated from ground measurements using algorithms based on Newtonian potential theory. Gravity measurements with an internal consistency of better than 20 μGal (1 μGal = 10−8 m/s2) were made on the tower at intervals of about 90 m using a single LaCoste‐Romberg model G gravimeter. Field measurements of gravity (using the same instrument) and corresponding geodetic positions were performed at 77 points within a radius of 5 km from the tower. These and other gravimetric data within a radius of about 220 km were used to perform the upward continuation using two independent computational techniques. One is least squares collocation, which is based on a statistical interpretation of the local gravity field, and the other determines a local harmonic expansion of the field from the given data. The upward continuation from both methods gave almost identical results and is estimated to have an uncertainty comparable to the in situ measurements. The results of the experiment show a substantial departure from the inverse square law, asymptotically approaching about 500 μGal at the top of the tower, with a standard deviation of better than 40 μGal. This indicates that there is a non‐Newtonian attractive force which falls off rapidly with elevation.
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