Research On Underwater Environment Information Recognition And Transmission Technology

In recent decades, the impact of underwater acoustic detection technology in the field of military and civilian aspects in China is getting bigger and bigger. However, as an inportant branch in the field of underwater acoustic, the development of the technology still has limitations. This thesis focuses on the finding study methods of speed, distance and direction of close underwater environment targets. Mixed frequency modulated signal is used as detection signal and the echo signal processing is combined with fractional Fourier transform and array signal processing technology.Firstly, the paper analyses the basic situation of the underwater environment and researches on the background noise and Doppler effects in the underwater environme nt of the communication process. According to theoretical analysis of linear frequency modulated signal’s characteristics, the paper introduces a new type of detection signal called mixed frequency modulated signal and gives a brief description of the nature and detection performance of the signal. Secondly, the paper conducts a research on the principles of fractional Fourier transform of linear frequency modulated signal and fetches out the fractional Fourier transform of mixed frequency modulated signal and analyses its best transform order, the results of which are used to calculate the frequency rate parameter and doppler scale factor of echo signal. Then according to the principles of Doppler effect, the paper puts forward a speed parameter estimation method of underwater moving targets. Thirdly, the paper points out the feature that the fractional Fourier transform domain of mixed frequency modulated signal will form an impulse and proposes a distance parameter estimation method of underwater moving targets through the use of echo signal’s coordinate values in fractional Fourier transform domain. Finally, the paper gives a azimuth angle parameter estimation method of moving targets mainly based on the signal processing and filtering of the echo signal, then the angle information of the targets will be obtained with the realization of DOA estimation and MUSIC algorithm of echo signal through the signal sepration.Based on the finding study method s of speed, distance and direction of close underwater environment moving targets by using mixed frequency modulated signal, the paper puts forward a segment search method of best transform order of the echo signal and further tests the correctness of speed and distance parameter estimation methods of underwater moving targets. Meantime, based on the above algorithm for DOA etimation of mixed frequency modulated signal, the paper completes the validation of azimuth angle parameter estimation method of underwater moving targets. Finally, combined with the method of underwater moving target parameter estimation, the paper gives the whole block diagram of moving target detection and its detection scheme..