VSA Gravity Meter System: Tests and recent developments

A vibrating string accelerometer (VSA) sea gravity meter with electronics for digital readout has been assembled, tested, and used by the Woods Hole Oceanographic Institution. The VSA meter is installed in a portable van laboratory that also contains a digital computer for automatic logging of gravity, magnetic, and ship's velocity information. Two years of testing and use of the VSA gravity meter at sea are summarized. Tares and remaining sensitivity to variations in ambient temperature and supply voltage are inferred to be due primarily to the oscillator amplifiers. Improved oscillator amplifiers will be installed. During December 1969, the VSA meter, together with a gyrostabilized LaCoste and Romberg (L&R) sea gravity meter, were operated aboard the RV Atlantis 2. The values from the VSA and L&R gravity meters were both reduced using identical navigational information. Resulting profiles of free-air anomalies derived from both meters differed by up to 15 mgal and led to the identification of a malfunction in the cross-coupling circuitry of the L&R meter. Identical malfunctions have been subsequently identified in three other L&R sea gravity meters.