. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography type of shipborne gravimeter which measures a change in frequency of vibration which is proportional to the acceleration of gravity (Wing, 1969K Ships larger than several thousand tons displacement are favored as platforms for making gravity measurements because of their stability. The problem of extraneous accelerations is averted and the highest accuracy is achieved in the sea-floor gravimeter which is encased in a water-tight chamber, placed on t
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography type of shipborne gravimeter which measures a change in frequency of vibration which is proportional to the acceleration of gravity (Wing, 1969K Ships larger than several thousand tons displacement are favored as platforms for making gravity measurements because of their stability. The problem of extraneous accelerations is averted and the highest accuracy is achieved in the sea-floor gravimeter which is encased in a water-tight chamber, placed on the ocean bottom, and operated by remote control through an electrical cable to the surface ship. Accuracy of navigation during gravity measurements is essential because the E*6tv*<5s correction arising from the Coriolis force experienced by moving bodies on a rotating earth varies significantly with ship's speed, course, and position (Worzel and Harrison, 1963). The observed value of gravity minus the value predicted by the in- ternational formula for the earth's field gives the free-air anomaly (fig. 25). Bouguer anomalies are computed from the free-air anomalies after an allowance is made for the density deficit of water with respect to crustal materials and directly represent density variations below the sea floor. The corrected gravity measurements can be contoured to delineate gravity "highs" and ."lows" if enough measurements over an area are available (fig. 26). Hypothetical reconstructions of buried geo- logical structures can be computed from individual profiles. As in the magnetic method, the interpretation of gravity measurements is ambiguous M. Figure 24. The Graf-Askania and La Coste-Romberg gravimeters measure the force of gravity (g) by its effect in displac- ing a weight ( kd ) balanced by a spring (From Nettleton, 1971, fig. 6). 788. Please note that these images are extracted from scanned page images that may have been digitally enhanced
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