Theory and evaluation of the LaCoste and Romberg three-axis inertial platform for marine gravimetry

Abstract In 1972, the Earth Physics Branch of the Canadian Department of Energy, Mines and Resources acquired a LaCoste and Romberg Inc. air/sea gravimeter complete with three-axis inertial platform. Since then, in cooperation with the manufacturer, a thorough evaluation of this system for regional applications has been undertaken over two field seasons. In 1972, the instrument was operated over the Halifax Test Range where direct comparisons with underwater measurements indicated that the system as constituted gave results which were accurate from + or -5 to + or -10 mgal (+ or -1sigma ), with position updates at about two hour intervals. In general, the errors were greatest when the gyro precession rates were large and hardware modifications were made to reduce this effect. A second survey in Queen Charlotte Sound was made in 1973 to evaluate improvements designed to reduce the gyro precession rates. An analysis of crossover differences indicated that accuracies in measuring gravity of 3 mgal (+ or -1sigma ) using the inertial platform under open sea conditions is achievable. The accuracy of the Eotvos correction determined from inertial data is intermediate between that obtained using Loran-C in the rho-rho mode and hi-fix.