A nonreciprocal time reversal detection method for detecting the forward scattering of the small target in shallow water

The strong direct wave makes difficulty to detect the forward scattering of the underwater object.The passive NonReciprocity-based Time Reversal(NRTR) technique is used for the forward scattering detection problem in this paper.A Weighted Fourier transform and RELAXation based channel estimation method(WRELAX) is combined with NRTR to improve the detection performance.The detection is achieved by detecting the variations of the acoustic filed caused by the forward scattering,the iterative threshold classifiers is applied to get the detection results.The frequency of the source signal ranges from 15 kHz to 30 kHz in the at-sea experiment.The signals gathered from experiment at sea are processed using the proposed method.Comparing with the classical NRTR detection method,the WRELAX-NRTR detection scheme decrease the background perturbations from 10 dB to 4 dB,the false alarm probability is reduced consequently.In addition,the detection is robust for the underwater noises,different source depth,crossing position and dynamic acoustic channel.