PERFORMANCE OF A SUPERCONDUCTING GRAVITY GRADIOMETER

We report the laboratory operation of an rf SQUID - based superconduct ing gravity gradiometer designed to measure from an aircraft, off-diag onal components of the earth's gravity gradient tensor. A detailed num erical model of the multi-mode electromechanical system shows excellen t agreement with the experimental observations. We have demonstrated a common mode rejection ratio to linear accelerations of 180dB, as well as 60dB of active thermal compensation below 0.01Hz. Short term measu rements show the instrument to be SQUID noise limited at 0.5 Eo/square -rootHz in a frequency band from 50mHz to 1Hz. After correcting for th e remaining effects of thermal fluctuations and flux creep the noise b elow 50mHz has a 1/f characteristic which is also dominated by the SQU ID.