The Study On Underwater Acoustic Target Detection Method Based On Underwater Vehicle

With the modern ship radiation noise spectrum significantly reduced,the intensity of the underwater acoustic signal received by the passive sonar is correspondingly reduced.In the case of distant sea,the actual received signal to noise ratio is very low.The conventional linear detection method can achieve good detection effect under the condition of high signal-to-noise ratio.However,when the signal-to-noise ratio is very low,the target signal is almost completely submerged by strong noise,and the detection effect is extremely poor,greatly reducing the detection probability.After detailed introduction of the existing signal detection methods,Improved Empirical model decomposition(EMD),The Stochastic Resonance(SR)of multi-frequency large parameter signals was realized.Improved conventional Intermittent chaos detection method.It's hoped that more effective weak signal detection method can be obtained.The main contents of the full text are as follows:The types and the status of domestic and overseas research of underwater vehicle were introduced.The present methods of signal detection and their research status were introduced in terms of time domain,frequency domain,time frequency domain and airspace.The basic theories and steps of empirical mode decomposition were introduced,and then some problems existing in normal empirical mode decomposition were analyzed.Then the improvement methods based on empirical mode decomposition were introduced,and some defects of various improvement methods were analyzed.With the thought that the aid of noise and complementation,the existing empirical mode decomposition method was further improved.The time domain decomposition results,reconstruction errors and iteration times of various improved methods were compared through experimental simulation,which proved the superiority of the proposed method.In this paper,the bistable Stochastic Resonance of the nonlinear processing method is used to detect the underwater acoustic signal.The experimental results show that the proposed method can detect the target signal with low SNR(-20 or even-30dB)Method,which can break the shackles of very low SNR,and has a good application prospect and research value.In order to realize the signal detection under the condition of lower SNR,this paper introduces the adaptive step size based on the Duffing chaotic system,and tests the measured signal at the optimal excitation frequency.The existence of the target signal is judged by observing whether there is two consecutive intermittent chaos in the time domain output.Then the envelope of the intermittent chaotic signal is obtained by Hilbert transform.Finally,the envelope spectrum is obtained by using the1(1/2)dimension spectrum,and the exact value of the frequency difference?f is obtained,which can calculate the exact value of the frequency of the signal to be measured.In this paper,the proposed method can achieve a lower SNR(-30dB or less)than the conventional detection method.Compared with the general chaotic detection,this method can realize self-adaptation.It's unnecessary to specify different excitation frequencies and chaotic thresholds for different frequencies to be measured.The effectiveness and superiority of the proposed method are verified by experimental simulation.