The Studies On Passive Tracing Of Underwater Moving Target

Passive detection and location in underwater acoustic has always been the focus of researchers. As the further research on the underwater acoustic field, the matched field passive source location is proposed. While TMA (target motion analysis) make full use of the data during a time period to estimate the state of the moving target. They are the two new hotspots in passive location researching field. According to these two technology, this dissertation explores the new way for passive source location which can be used in single (vector) hydrophone based on the analysis on the underwater acoustic vector field modeling.The model of acoustic vector field at low frequency based on the ray theory is established first. Then the transmission loss curves between ray theory and mode theory are compared, which show that the ray model is a good approximation to the mode theory in near distance. And then the interference phenomenon of pressure and velocity is discussed, which shows that the pressure and the horizontal velocity have the same interference pattern. Based on the analysis of the acoustic interference phenomenon, this dessertaion deduced that the interference pattern is hyperbola cluster. The target motion state (speed, depth and the nearest distance) will determine the shape of these hyperbola clusters. The different affect of target traveling in shallow water and deep water to the interference pattern is discussed. Hough transform is a usual method for the image edge detection. It has been used in the underwater acoustic field for estimation combined with time-frequency analysis, exemplified by estimate the frequency slope of the LFM signal with wigner-Hough transform. This dissertation uses the Hough transform to distill the parameter of the hyperbola curve to estimate the target state (speed, depth and the nearest distance) .Then, this dissertation analyzes physical meaning of the interference period theoretically and discusses the location methods. The application of the interference spectrum in underwater acoustic is also discussed. It can be used to eliminate the wake effect of the moving target and the strong instantaneous narrowband disturb which could have some practical value in the short distance detection. The passive tracking system for underwater high speed target has already stepped into the realizing stage. Passive ranging technology needs no informations of the target signal form, which would improve naval shooting trial efficiency greatly.The main obstacles for the passive tracking system are the Doppler effect and multipath effect.The Doppler compensation is necessary for the high speed target tracking because of the high Doppler coefficient in underwater acoustic environment.The second order Doppler coefficient is deduced and the affect to the first order Doppler compensation is discussed.And then this dissertation analyzes the Doppler coefficient difference between the different acoustic ray caused by the high speed moving target.The purpose of all these analysis is to overcome the Doppler effect.To obtain high estimation precision, the long baseline system is needed. However, the traditional long baseline positioning cost expensive computation in absence of target initial position,which will be even worse for the high speed target because of Doppler compensation.According to the passive tracking system composing model , a noval method is presented that the long baseline associated with virtual short baseline.Using this method, the computation burden is lightened with no increasing of system facility.To overcome the multipath effect, an expert system for the short range tracing target is designed,which can reduce the time delay estimation error in multi- correlation peaks.This expert system guarantees the effectiveness of the passive tracing measurements for the high speed target.