Compensation for motion-coupled error in a superconducting gravity gradiometer.

The superconducting gravity gradiometer (SGG) is composed of a pair of separated accelerometers, the outputs of which are differenced to yield the gravity gradient. Due to misalignment between the sensitive axes of the accelerometer and imperfect balance between its parameters, the motion of the platform is coupled to the gradiometer output. The motion of the platform is more violent in an aviation environment than in the laboratory by four to six orders of magnitude, and the motion-coupled error emerges as the dominant factor, limiting the resolution of the gradiometer. Therefore, a method of error compensation is needed to subtract the motion-coupled error from the gradiometer output. In this article, we propose a method of error compensation for the SGG. We establish an error model of the Γzz SGG, the recursive least-squares algorithm is proposed to estimate the parameters involved in the model, and the estimated motion-coupled error is subsequently generated based on the error model and monitored motion data of the platform. The results of simulations showed that the accuracy of the accelerometers should not exceed 10-6 m/s2/√Hz, while that of angular accelerometers should not exceed 10-6 rad/s2/√Hz in order to compensate output error of SGG to 1 E. We conducted experiments on the SGG to verify the proposed method of error compensation, and the results showed that the residual noise of the gradiometer after error compensation was reduced by one order of magnitude in the range of 0.01-0.1 Hz.