Preliminary free-air gravity map, Norton Basin, Alaska

Gravity data shown here were measured with LaCoste and Romberg sea gravimeter S-53 mounted on a 3 axis inertial platform (LaCoste and others, 1967, Valiant and LaCoste, 1976). Primary navigation was by satellite, integrated with course and speed measurements from doppler sonar and gyrocompass. Gravity data were filtered prior to recording with a four-minute averaging filter to remove high frequency effects of ship motion and with an 84 minute notch filter to remove Schubert-period oscillations. The gravity computer applied a correction for "inherent" cross coupling error (LaCoste and others, 1967).