Key Techniques For Gravity Gradient Measurement Based On Rotating Accelerometers

Gravity gradient measurement based on rotating accelerometers is an effective method to achieve high-precision gravity gradient signal.In this measurement method,the gravity gradient signal is modulated to a frequency twice the known rotational speed of the turntable,and the gravity gradient signal can be obtained by signal demodulation at a double frequency.The thesis studies the various problems in the gravity gradient measurement,reveals the internal principle that the gravity gradient signal is modulated to double frequency,and proposes a gravity gradiometer calibration method based on centrifuge,and analyzes the influence of principle error on measurement results.The main work and innovations of this paper are as follows:（1）.Using the method of segmentation calculation,the formula of the accelerometer output in the gravity gradient measurement based on rotating accelerometers is derived.Based on the formula,the mathematical model of gravity gradient measurement is given.The principle that the gravity gradient signal appears at twice the known rotational speed of the turntable is revealed,which provides a theoretical basis for error compensation.Based on the coordinate transformation formula of gravity gradient tensor matrix,the influence of the installation method of gravity gradient sensors on the measurement results is analyzed,and the symmetry invariance of gravity gradient tensor matrix is proved.（2）.The demodulation methods in the gravity gradient measurement are studied in the time domain and frequency domain respectively.The performance of various demodulation methods under noise interference is compared by simulation experiments.The results show that the methods in the time domain has better stability.Compared with the methods in the frequency domain,the accuracy of demodulation results in the time domain is relatively low.The methods in the frequency domain need to preprocess the data by using spectral line enhancement filtering.This process will affect the results,and high-precision phase compensation is required to achieve high-precision gravity gradient signal.（3）.A new method for gravity gradiometer calibration using centrifugal gradient is proposed.The relationship between the angular velocity of the centrifuge and the output of the gravity gradiometer is given.The method uses the centrifugal force field generated by the rotation of the centrifuge as a standard gradient signal,and the calibration of the gravity gradiometer is realized by the comparison between the output of gravity gradiometer and the standard signal.Based on this method,the development of the gravity gradiometer can be realized more easily.（4）.The principle error in the gravity gradient measurement is studied.The principle error is determined by measurement method.It can not be eliminated by improving the stability of measurement environment,and also the performance of measurement components in the gravity gradiometry.This paper analyzes the influence of the principle error on the gravity gradient measurement.The results show that the principle error has a direct relationship with the baseline length.When the baseline length reaches 100 meters,it will seriously affect the measurement of theΓxz component in the gravity gradient tensor.The component will be overwhelmed by the principle error,making it impossible to measure this component.When the baseline length is 0.4m,the effect of the principle error on the gravity gradient measurement is about1?10^-5E,which is negligible.That is,in the short-baseline gravity gradient measurement,it can be considered that the principle error has no effect on the measurement results.