Research On Key Methods Of Target Detecting For Underwater Monitoring System

Underwater Monitoring System is a sort of integrated measure and test system, which is under water for monitoring marine environmental parameters. It can measure ocean current, ocean temperature, sound velocity and other marine environment parameters. Underwater Monitoring System is made up of pedestal and floater, and pedestal comprises linear sonar array, ADCP, control system and information processing system, floater comprises round sonar array, SVTP and electronic compass. While working, the control system makes floater out of the pedestal to measure marine environmental parameters. In order to keep the floater safe, the uniform linear sonar array must detect the dangerous target (fishing boat, merchant ship, warship and so on) before the floater comes out of the pedestal. When the floater is working, the uniform round sonar array need detect dangerous target real-time in order to protect the floater from being destroyesd. Once detecting the dangerous target, the foater must be taken back. Based on the above application background, the thesis makes some researches on beam forming, DOA estimation and spectrum detection, and validates the algorithms by simulation. The thesis is organized as follows.1. In order to satisfy the signal delay of scanning beam in uniform linear sonar arrays, the thesis discusses and researches several delay filtering methods. Research results show that fractional delay filtering algorithm based on Lagrange interpolation is simple and is easily applied to engineering. The algorithm can delay signal exactly without additional delay and the precision is high.2. For solving the problem of DOA estimation in uniform linear sonar arrays, this thesis proposes three kinds of algorithm based on angle of carrier phase, double angle and triple angle respectively, and then analyzes the estimation performance of these algorithms. Numerical simulation results show that the solution of the algorithm based on triple angle is the highest and the estimation range of DOA is the largest in these algorithms, so it is fit for detecting target.3. For the purpose of DOA estimation for two coherent signals, a new approach based on carrier phase for DOA estimation is proposed. Research results show that the resolution and precision of the new approach are better than that of spatial smoothing MUSIC.4. According to the property of broadband target noise, the thesis presents a method of DOA estimation for uniform round sonar arrays and introduces joint interpolation-filter-delay-extract method. In addition, in order to remove the fixed delay in the joint method, a delay filtering method without additional delay is proposed. Research results show that the DOA method is simple and available, and the precision is high. The results also show that the joint interpolation-filter-delay-extract method without additional delay can delay signal exactly and applies to the trial of DOA estimation for uniform round sonar arrays successfully.5. For estimating frequency of echo signal, the thesis introduces MUSIC method in frequency domain beam-space (Frequency Beam MUSIC). The signal model for Frequency Beam MUSIC is presented and the property of frequency estimation errors is studied. Numerical simulation results show that Frequency Beam MUSIC can estimate frequency of sine wave in additive Gaussian white noise and the precision of Frequency Beam MUSIC is equal to that of MUSIC, but the signal-to-noise ratio (SNR) resolution threshold of Frequency Beam MUSIC with reduced dimensionality is lower than that of MUSIC, the computation cost is also lower than that of MUSIC, and the Frequency Beam MUSIC is more suitable for engineering application.Target detecting comprises signal delay, DOA estimation, frequency estimation and so on. Making use of the above algorithm can decrease the computational complexity of signal delay, simplify the system structure of DOA estimation and improve the resolution of frequency estimation. These algorithms and simulations lay the foundation of target detecting for Underwater Monitoring System.