Result of the tests conducted by a newly developed helicopter borne gravimeter system

Copyright (c) 2006-2007 Japan Science and Technology AgencyAirborne gravity measurement has long been a desirable goal for exploration geophysicists. Success of the air-borne gravity surveys mainly depends on determining the three-dimensional(3-D) position of the moving platform(i.e. airplane/helicopter). Recent advances in technology, especially in Global Positioning System(GPS) have made it possible to determine the velocity and 3-D position of the moving platform with greater accuracy. Taking these advantages of the GPS technology and using a gravimeter system newly developed, helicopter-borne gravity measurements were successfully carried out over the Kanto district of Japan during May, August and December 1999. This new gravimeter system is composed of a servo accelerometer sensor, a stabilized platform, an optical-fiber gyroscope to control the stabilized platform, a data processor & controller, onboard GPS receivers and a land-based GPS receiver. Gravity acceleration and GPS positioning data were collected at intervals of 0.1sec and 1sec respectively. The GPS positioning data were used to compute helicopter vertical acceleration, Eoetvoes, altitude and latitude corrections, which were applied to the measured gravity acceleration. The gravity acceleration data collected were processed and necessary corrections were applied. Numerical filtering was carried out to remove high frequency noises present in the data. The observed free-air gravity anomalies were quite comparable with the upward continuation of the anomalies observed on the ground. Thus the preliminary analysis of the test data demonstrates the feasibility of helicopter-borne gravity measurements. (author abst.