Technical report on a portable gravity meter platform and first test results

Abstract

This report describes the new portable platform and gravity meter system which has been assembled at the Woods Hole Oceanographic Institution. It consists of three functionally distinct parts. The first of these is a recently developed gyro-stabilized two-axis platform. This platform has been designed to carry the vibrating string accelerometer (VSA) and its associated oven assembly as the gravity sensor. The new platform represents a major reduction in both size and weight over other platforms suitable for gravity measurement. The second major part of this system is a new gravity readout which interfaces with the VSA, processes the VSA output, and prepares the resulting filtered acceleration data for output to the acquisition system. The readout has been designed to allow flexible use of the gravity system on a variety of vehicles, including ships, submarines and aircraft. The third part of this new meter is the data acquisition system. It consists of a microprocessor interfaced to a Kennedy 9-track tape drive. Both the platform and the readout are connected to the microprocessor. Results are presented from Endeavor cruise 88 that demonstrate the ability of the platform to stabilize the gravity meter and for the gravity system to produce raw data with a resolution of 48 milligals at a sampling rate of 10 Hz. Digital signal processing techniques which were used to filter the data and extract the gravity signal with a resolution of 0.48 milligals are also discussed.