Research Of Validity Of The Vibration Measurement On Absolute Gravimeter Based On Interferometric Technology

The Absolute Gravimeter?AG?is basic device which is adopted to detect the features of the geophysical field.And the information of gravitational field from the detection of the AG is considerably important for the application and research of geodynamics,seismology,space physics and etc.The measurement accuracy of the AG is related to the validity of the measured gravitational field.Nowadays there are two types of AG,the AG based on laser interferometer and the AG based on atom interferometer.During the measurement of the former one,there are plenty of influence factors that can affect the accuracy of results,such as the test site,the offset between the optic center and mass center of the falling corner cube,the vibration on the reference mirror and etc.Among all these influence factors,the interference of the vibration is the largest influencing one.Vibration isolation systems such as Super Spring system and seismometers are adopted to solve this problem in order to improve the accuracy of the AG.This article introduces the application,development and background of the AG.The commonly used methods in vibration isolation are also summarized and the experiment scheme of this article which aims at detecting the amplitude and direction of micro vibration based on space optic interference with phase generated carrier method to verify the validity of this goal.The work can be mainly divided into three parts:theoretical analyses,algorithm simulation and experimental verification.In theoretical part,working principles of gravity measurement and the AG are described.And then errors such as vibration error,reference error,falling error and system error are also analyzed.The theory of phase generated carrier method?PGC?and interferometry are introduced and details of errors on each step are given.In the algorithm simulation part,we use Matlab and Simulink to testify the validity of the algorithm.Finally,in the experimental verification part we design a Michelson Interferometer based on PGC and interferometry.The validity and accuracy of this system are verified and the details are shown below:?1?Setting up the whole interferometer system in an horizontal plane,then the phase of the interference signal is modulated by the piezoelectric ceramic?PZT?and the signal is detected with self-designed photoelectric detector.The frequency of initial referenced vibration signals are given by 20Hz,40Hz,60Hz,80Hz.After phase compensation of the demodulation,the demodulated vibration signal is compared with the amplitude and frequency of the PZT which is calibrated before to validate this algorithm.?2?Changing the measuring prism from horizontal direction into vertical direction and adopting an extra vibration signal generator.Vibration isolation platform Minus K and vibration detector 991B are used to make comparison with results from the interferometer system synchronously in order to validate this system.Comparing with the vibration detector,it can be seen that the accuracy of the interferometer can match with that of the detector in 10^-8m and the range of signal frequency it can detect is less than 100HZ,which quite meet requirements of the micro vibration measurement.And this result can also help broaden the application of interferometer and provide new guideline for vibration isolation.