Research On Optical Measurement Methods And Key Technology Of Seismic

Recently, crustal activities are more and more frequent, the earthquake prediction hasaroused more and more attention. People try to find a better way to breakthrough in predicting.The application of the laser interferometer in geophysics, crustal deformation, earthquake andtsunami monitoring shows advantages, comparing with the conventional seismometers: highsensitivity, wide bandwidth, large dynamic range. The paper carried out the research on therelated technology of the laser interferometer, focusing on the application in measuring smallvibration. The study is mainly about the key technology in monitoring the seismic with theinterferometer, including the system design theory, interferometer noise analysis, the designof the integrated interferometer, the vacuum environment building and the prototype testing.The main work carried out of this paper is as follows:1. At first, we derived the transfer function of the entire system, including thephase-frequency characteristics and the amplitude-frequency characteristics. After thetheoretical analysis of the laser interferometer and the demodulation system respectively, weget the transfer function by integrating the derivation. Second, based on the displacementmeasuring principle of the optical interferometer, the effects of the laser noise in theinterferometer measurement accuracy has been studied; Finally, according to the principle, thelayout structure of seismic monitoring system is designed.2. Secondly, the production method of the integrated interferometer is proposed. Weanalyzed the impact of the environment factors on the unintegrated interferometer in theory,described the necessity for integrated style, and detailed the design, including the externaladjustment structure and the package design. According to the principle of the long-baseinterferometer, the structure of the beam position detection system is designed.3. And then, mainly for reducing the atmospheric effects on the optical interferometer, webuilt a vacuum system. At first, we studied the objective factors that affect the measurementprecision of the seismic monitoring system, proposing some disincentives, focusing onchanges in refractive index of the atmosphere air caused by the atmosphere pressurefluctuation and the atmospheric disturbance. Then in order to reduce the constraints inmeasurement accuracy caused by the atmospheric environment, we designed a vacuumsystem, matching the optical interferometer system. At last, we tested the entire vacuum for grasping the performance of the system.4. Finally, we did some measurement experiments in the performance of the monitoringsystem prototype. At first, we calibrated the entire system, including the resolution of thesystem, dynamic range and frequency band. Then the measurement stability of the wholesystem has been tested, exhausting a single-side pipe for studying the impact of air conditions.Finally, we analyzed the noise spectrum of the optical seismic monitoring system, includingeach step of the installation process, by comparing the noise situation, explored the rootcauses of the noise.At last, the prototype was tested. The total length of the prototype is22m, in thefrequency band10Hz~90Hz, the system’s measurement resolution can reach0.0098nm,dynamic range over120dB. Experiments proved that the optical seismic monitoring system,based on the balance arm Michelson interferometer principle, can be used to measure thesmall vibration of the earth, while it has a high resolution, wide frequency band, largedynamic range.