Study On Gravity Gradients And Its Application In Test Of Weak Equivalence Principle Based On Torsion Pendulum Method

Equivalence Principle(EP)is one of the hypotheses of the General Relativity,almost all theories that attempt to unify the gravity and other three fundamental interactions demand the violation of the EP.Therefore,a high accurate result of testing the EP,whether yes or no is of important scientific significance.At present,the most accurate measurement precision(?12<1.8×10-13)of the test of EP on the ground,is reported by E?t-Wash group from the University of Washington.The experimental instrument they adopted is a rotational precise torsion pendulum with a tungsten fiber.In the past seven years,Center for Gravitational Experiments(CGE)of Huazhong University of Science and Technology improved the E?t-Wash group's experiment by adopted a quartz fiber instead of the primary tungsten fiber.The results of the research of the CGE shows that the Q-factor of the experimental instrument with the quartz fiber can be improved about two orders,and the measurement precision may reach at 10-14 level.We analyze the gravity gradient effect which is a main systematic error source in the CGE's test of WEP.The result shows that the uncompensated gravity gradient effect from the coupling term of the dominated gravity gradient multipole moment component q21 and the relative multipole field component Q21 contributes to an uncertainty of 1×10-11 on the E?tv?s parameter.We make a Q21 compensation to reduce the effect by about 20 times,and the limit of the test precision due to this coupling is improved to a level of a part in 1013.Obviously,the effective measurement and compensation of the gravitational gradient effect in the test of the weak equivalence principle is great significance to improve the test accuracy.The gravity gradient measurement can offer an efficient way for resource explorations in earth since the gravity gradient data could be used to reveal underground mass distribution.The torque type gradiometer designed by E?tv?s made a great difference on the petroleum industry in early twentieth century.The gradiometer has been used for gravity gradient measurement since its low cost,relatively high measurement precision and easy to field measurement.Nevertheless,it is relatively inefficient and with the precision of about 1 E mainly caused by the static operating mode.In this master's thesis,we develop an improved torque type gravity gradiometer to improve the measuring efficiency,which is based on the dynamic modulation.The dynamic modulation keeps the gradiometer rotating on a turntable steadily,measures the deflection angle of the torsion pendulum continuously and then obtains the gravity gradients.The result shows that the measurement cycle of the improved gradiometer can be decrease to one-quarter of the measurement cycle of the traditional gradiometer at the same measurement precision level.The improvement of the measuring efficiency is great significance for oil exploration,seismology,geology and inertial navigation.APES is selected to estimate the amplitude of the target signal according to the characteristics of the experimental signal and the requirements of the experimental signal processing in the improved gravity gradiometer.On the one hand,the original APES applies to the complex signals.On the other hand,the experimental signal of the improved gradiometer is real signal.Therefore,we improved the algorithm and let it meet the requirements of the improved gravity gradiometer experimental signal processing.The algorithm simulation results and experimental data processing results show that the improved algorithm can estimate the amplitude of target signal with high accuracy.