The Study Of Underwater Target Detection And Application Based On Time Reversal Theory

The work of this thesis is based on the Time Reversal Theory. According to the problem of small target detection which is sunk on or buried in the seafloor in the strong reverberation background, we analyze and validate with theory and experiment about the essential problem of small target detection which is desired to be resolved in the complex shallow sea environment. Work of the paper includes theory analyzing and simulation about time reversal method on mine detection, and includes some experiment achievement and work in a certain acoustic detection foundation project.The problem of buried target detection in the strong reverberation environment is all along important study content. General methods are modeling or predicting process, which direct treat with reverberation signal. Then we can filter out reverberation signal and enhance signal-reverberation ratio. But, because of the complex forming mechanism of reverberation, it has randomness of the representation and regularity of the statistics. So a long time, although anti-reverberation of some of the technical progress has been made, but there are still large requirement for further research and development. Time reversal method has unique advantages as a self-adaptive focusing method with nothing prior knowledge of channel conditions, and it has inhibiting effect while reverberation and noise signals have a certain extent. So, time reversal method has good prospects of engineering application than traditional active sonar detection methods. Especially for mine detection in the shallow sea, it has strong attraction in the complex environment which has strong reverberation and strong absorption.Firstly, the paper has a brief introduction of the origin of time reversal method, the development and the status quo. The general theory of time reversal methods are reviewed and summarized, and the domestic and foreign researching status and achievements of this method are introduced. Based on ray acoustics theoretical model, the detection problem is analyzed and simulated about the target which in the underwater waveguide with time reversal method. It is proved that time reversal method is feasibility and robustness. And it need analyz and simulates further of the iterative time reversal method.Secondly, through simulation modeling and calculation of reverberation, the performance and effects of inhibiting reverberation and echo enhance of time reversal method about the sunk or buried target detection are more detailed analyzed. This laid a foundation of theory and method for further practical engineering application. The paper discusses the effects of noise and reverberation on the law and the robustness of a single target or multiple target detection by time reversal method.Thirdly, according to the strong reverberation and weak echo signal condition of buried target detection, the paper use match-filter and chaotic signal processing method for the time reversal processing to reduce reverberation intensity and signal extraction. The paper discusses the chaotic properties of reverberation, and uses chaotic model for the reverberation sequence modeling. Next, the paper do some analysis about the signal in the reverberation background based on the chaotic process method, and realize effective detection and extraction of target echo signal in the low signal-reverberation ratio background.Fourthly, this thesis study and analyze the experiment of time reversal detection of hanged and buried small target in the acoustic channel pool by single TRA (time reversal array) element, then get some result of underwater target detection, and achieve some useful experience about the practical engineering application of TRM (time reversal mirror). These result and conclusion have some reference value for further theory and application study.Finally, this thesis design and analyze the system programs and the essential technologies about time reversal detection method in the practical engineering application, and made some foundation for practical engineering application in the future. For the certain acoustic detection foundation project, a sixth channel arbitrary wave generator is designed and implementated.