Research On Performance Improvement Of Open-loop Fiber-optic Gyroscope And Its Application In Attitude Measurement Of Fiber-optic Vector Hydrophone

In recent years, intellectualized underwater weapons are developing rapidly. Due to the particularity of underwater environment, inertial navigation, attitude control and acoustic detection have become key technologies of underwater weapons. To fulfill applying and developing requirement of underwater weapons, performance improvement of open-loop fiber optic gyroscope(FOG) and its application in attitude measurement for fiber-optic vector hydrophone were studied. These researches provide theoretical and experimental basis for the underwater weapons'technical development of motion control and acoustic detection.To underwater weapons, because of its dynamic characteristic and requirement of low cost, open-loop FOG is an ideal inertial component. To specific structure of open-loop FOG, theoretical and experimental researches on gyro performance improvemen were investigated. The accuracy of modulation signal was improved by two-level wave table method, and also was the control precision of work point. Relative intensity noise(RIN) of source was suppressed to a certain extent by a new RIN subtraction algorithm, and the random walk was decreased. Temperature stability of the gyro was improved by temperature compensation. Noise on gyro signal was obviously suppressed by the wavelet de-noise method. The improved gyro was tested, and the result shows the performance of the gyro is obviously better than the imported open-loop FOG selled in our market.The measurement of fiber-optic vector hydrophone is based on body frame of itself. In a movement platform, measurement results with respect to changing body frame of fiber-optic vector hydrophone should be transformed to same reference frame. Due to particular requirement of vector acoustic signal processing, attitude transform algorithm for direction of arrival (DOA) estimation, signal fusion of four components and acoustic field calculation were studied. Due to FOG's characteristic of angular velocity output, attitude algorithms based on angular velocity measurement was deduced. Improved attitude algorithms were optimized under classical coning motion and sculling motion. The simulation result shows optimized algorithms have lower error.The error of attitude system was analysed, and the error equations were simplified under applying property of vector hydrophone. Error propagation equations on fixed platform were analysed, and error oscillation frequencies were gotton. Influence of attitude measurement error to DOA error was analysed, and its formulas were derived without and with acoustics noise. The formulas were proved correct by simulation result.Methods of calibration and initial alignment were studied. Position trial and rotation trial were needed when calibrating. FOG, accelerometer and compass's parameters of bias, scale factor and installation error can be calibrated. Because open-loop FOG is a kind of middle grade gyro in precision, initial alignment can not be accomplished only by FOG, magnetic compass was needed. Initial alignment was divided into two stage of coarse alignment and fine alignment. Precision of coarse alignment was analysed. Kalman Filtering technique aided by compass was used in fine alignment, and observability of Kalman filter was analysed. Simulation result shows that alignment precision can be improved by aiding of compass, the error of azimuth was decreased from 4°to 10′.Fiber-optic vector hydrophone attitude measurement system based on open-loop FOG was designed and developed. Comprehensive trials were done to attitude measurement system, including static trial, dynamic trial and sea trial combined with fiber-optic vector hydrophone. The result of sea trial shows that the precision of DOA estimation is improved highly after attitude correction, the standard deviation of azimuth was decreased from 6°~7°to 2°~3°.The main results of the dissertation are as follows:(1) Two-level wave table method was proposed to produce modulation signal of high precision. A new RIN suppress method was propsed to supress the RIN of source.(2) Due to the output of FOG is angular velocity, rotation vector algorithm and sculling algorithm were all optimized, and the error of algorithms were decreased.(3) The influence of attitude error to DOA estimation error was analysed. The formula of DOA estimation error with attitude error was given at no acoustic noise situation, and the formula of DOA estimation error's mean and variance with attitude error was given at acoustically noisefull situation. Big azimuth angle error can be caused by small attitude error at both situation when target pitch angle is big. So target pitch should be decreased in application.(4) Attitude measurement system of fiber-optic vector hydrophone based on open-loop FOG was designed and developed. Integrative electronics system was used for three-axis FOG module, so the volume and cost were decreased, and the clocks of three FOG were synchronized. The system can work under water, and the resuld of DOA estimation is correct after attitude transform. In the dissertation, open-loop FOG was for the first time applied for attitude measurement of fiber-optic vector hydrophone inland. The work is a real under water engineering application of FOG.