High Precision Direction Finding Technology Based On Single Vector Hydrophone Under Multi-target Condition

With the development of vibration and noise reduction technology,the radiated noise of underwater targets such as submarines is getting lower and lower.The noise of some quiet submarines in the frequency band above 200 Hz is no higher than the noise of the ocean environment.Due to the physical aperture limitation,there are many restrictions in the conventional acoustic pressure array,so the underwater target detection and direction finding technology based on ultra-low frequency vector hydrophones has become a research hotspot.However,there are usually interference targets such as surface ships in the actual ocean,and the ocean background sound field is also strongly anisotropic,which leads to the poor accuracy of direction estimation and the jump of the estimated value in the engineering application of the existing underwater multi-target direction finding technology based on the single vector hydrophone,and even causes the algorithm failure,which seriously restricts the application and extension of the vector hydrophone.Based on the research on the mechanism of radiated noise of underwater targets and the theory of vector sound field,the high-precision direction finding technology based on single vector hydrophone under the condition of multiple targets is deeply studied in this paper.Taking the spectrum characteristics of radiated noise of underwater targets as the starting point,the narrow band energy information carried by the target is enhanced by the stability weighting of the instantaneous phase difference of the line spectrum.Combined with the multi-target feature spectrum tracking technology,the outliers in the DOA estimation results are eliminated,and the highprecision and stable direction finding of multi-targets is realized.The main work of this paper is as follows:(1)Aiming at the problem of poor accuracy of conventional cross-spectrum direction finding under remote low signal-to-noise ratio(SNR)conditions,a weighted processing method of instantaneous phase difference stability of line spectrum based on single vector hydrophone was studied.Using the difference of instantaneous phase difference stability between the line spectrum of the sound source and the background noise,the high-precision direction finding of underwater multi-targets is realized by enhancing the line spectrum value in the sound pressure vibration velocity channel or the line spectrum energy in the frequency domain sound energy flow.The simulation results show that under the condition of low SNR,the performance of the acoustic pressure vibration velocity channel weighting method is improved by 14% compared with the conventional method,and the performance of the frequency domain acoustic energy flow weighting method is improved by 19% compared with the conventional method.(2)In view of the problem of poor multi-target observability in conventional crossspectrum method,a highly stable direction finding method for underwater multi-targets based on eigen-spectrum tracking is studied and explored on the basis of the stability weighting of instantaneous phase difference of line spectrum.The method uses multitarget characteristic spectrum locking tracking to suppress the continuous spectrum aliasing interference and eliminate the outliers in DOA estimation,so as to achieve the purpose of high-precision and stable direction finding.Simulation results show that the proposed method not only has good applicability in low signal-to-noise ratio,but also can resist certain instantaneous strong narrowband interference,and can effectively distinguish multi-target azimuth.Compared with the conventional direction finding method,the performance is improved by 24%.(3)A self-contained test prototype system is integrated with the existing experimental equipment,and the preliminary data validation of the researched direction finding method is carried out through the relevant sea trial data processing.The data processing results show that the proposed method has certain advantages over the conventional method under the condition of low signal-to-noise ratio and multi-target.The accuracy of underwater multi-target azimuth estimation is significantly improved and the stability is strong,and it has good observability.