Tow-ship Interference And Ambient Noise Suppression For Tail-direction Detection Of Towed Line Array

Towed line array sonar's detecting ability is affected by ambient noise and noise radiated by tow-ship which is angular spread caused by multipath arrival.Interval of array sensor,signal processing and displaying at terminal are key to determine sonar's detecting ability.Towed line array sonar's tail-direction detecting ability degrades significantly since interference from tow-ship noise.Tail-direction detecting ability needs to be improved urgently,otherwise it is impossible to detect threat target coming to attack self-guided by wake of tow-ship.In this paper,1/4 wavelength element interval array's response to continuous single-frequency signal and band limited noise is to be paid attention.Research shows that1/4 wavelength element interval array's end fire directivity is not symmetric which can effectively suppress tow-ship interference leaked to the tail direction.And,here combined sensor with null beam pattern is proposed to form a 1/4 wavelength interval array,which is more powerful to improve tail direction detecting ability than 1/4 wavelength interval array and also performs better than conventional null weighting.Computer simulation and pond experiment results agree well with theoretical prediction when simulate searching target especially from tail direction by preformed multi beams in tow-ship interference background.In order to overcome effect from oceanic ambient noise,in this paper,statistic characteristics of cross-spectral phase variance of split array is to be paid attention.Studies show that phase tends to uniform distribution with maximum variance in condition of low signal to noise ratio,while phase tends to exponential distribution with sharply decreasing variance in condition of increasing signal to noise ratio.It is proposed to weight each preformed beam with corresponding phase variance,which can not only restrain no-target-beam's output power of oceanic ambient noise but also enhance target-beam's output power of coherent signal,thus detecting ability is improved.Matrix item based processing is proposed to further explore the potential of temporal and spatial correlation matrix based array signal processing.Research shows that diagonal terms are self-correlation terms without ability of anti-isotropic noise,thus non-diagonal terms based array signal processing performs better in low signal-to-noise-ratio conditions.Better performance of anti tow-ship interference is achieved from odd oblique terms which is parallel to diagonal terms of correlation matrix of 1/4 wavelength interval array.To achieve lower detection threshold of displaying terminal,luminance function and color map of bearing-time-record are both modified.Studies show that lower detection threshold is reached by choosing hyperbolic tangent as luminance function and setting cold color map as black—light gray while warm color map as pink—yellow—white as well as combination of background normalization.