Some results from a study of the motion problems involved with gravity measurements at sea

Abstract

The periodic components of horizontal acceleration in a LaCoste and Romberg marine gravity meter suspended in gimbals [LaCoste, 1934, 1959, 1961; LaCoste and Harrison, 1961; Harrison, 1960] aboard a surface ship were investigated by determining the harmonic distribution in the horizontal accelerometer (ham) records. When horizontal accelerations are impressed upon the meter, the hams respond with an electric signal which is used by an analog to compute the second-order (Browne) correction [Browne, 1937; Vening Meinesz, 1941]. The long ham records the motion response of the meter in the fore and aft direction along the ship, and the cross ham records the motion response of the meter athwartships. The data available for this study were taken during April and May, 1961, with LaCoste and Romberg marine gravity meter 7 (using hams with pendulums of 60-sec period) aboard the USNS Dutton (T-AGS-22, with an over-all length of 140 m and a beam of 19 m) in the North Atlantic Ocean. A total of 44 hours of records, taken on four different days during a one-month period, was available. For the same period, the Sea and Swell Section of the Oceanographic Division of the U.S. Navy Hydrographic Office made a hindcast study to determine the wind, sea, and swell characteristics and made their results available for the present investigation.