The Research On Key Technology Of Very Low Frequency Underwater Acoustic And Seismic Wave Joint Detection

The rapid development of noise and vibration reduction and mute technology in modern submarine has greatly reduced the level of high-frequency noise.Passive sound characteristics based on low-frequency(LF)/very-low-frequency(VLF)bands have become effective detection methods for quiet submarines,but their potential has not yet been fully explored.The LF/VLF radiation noise excited by the underwater target is coupled to the ocean bottom and propagates in elastic waves to form an ocean bottom seismic wave field.Its dispersion and polarization characteristics can be used to detect and identify underwater targets.Utilizing the joint detection method of underwater acoustics and seismic waves,it provides useful explorations for effectively solving the problem of passive detection of existing VLF sources in water.Focusing on the passive detection of the VLF ocean bottom seismic wave,this paper mainly studies the following four aspects:(1)Theoretically model and numerically calculate the underwater acoustic field and seismic wave field near the ocean bottom interface.Including Scholte wave polarization,dispersion,propagation attenuation and other physical properties,especially in the polarization characteristics near the bottom,it provides new ways for underwater target detection and classification and identification.(2)Based on this,fully utilizing the underwater acoustic field and Scholte wave field information generated by source in water to obtain complete location information estimation of underwater targets:Polarization filtering technology is used to achieve target separation.The DOA estimation of underwater targets is performed by using multi-component beamforming technology.The underwater target distance estimation is achieved by using the velocity difference between the water direct acoustic and the ocean bottom Scholte wave.(3)Using COMSOL multiphysics software finite element method to calculate the typical ocean bottom physical characteristics and underwater target detection methods such as DOA estimation and distance estimation,the performance and theoretical feasibility of the method are verified.(4)In order to verify the underwater sound field and seismic wave field near the seabed,a set of very low frequency hydroacoustic and seismic wave seven-component recording system was developed in cooperation with the National Seismological Bureau of China.Based on the simulation of VLF passive detection of a typical waveguide near the ocean bottom,the study found that:(1)The direct acoustics and the Scholte wave multi-pass distance measurement method do not exceed 2%of the target distance within 5km.(2)7-component acoustic and seismic wave CBF and MVDR beamforming azimuth estimation method is significantly better than the four-component vector hydrophone,and the estimation error is approximately 10 times smaller at the same SNR.(3)The use of polarization filtering method to preprocess the signals of water direct acoustic and ocean bottom Scholte wave time-domain aliasing can slightly increase the accuracy of the horizontal azimuth angle estimation.(4)The joint method of acoustics and seismic waves detection can detect the complete location information of near-ocean-bottom target sound the source.(5)The numerical experiment preliminarily verifies the effectiveness of the joint detection method of the low-frequency underwater acoustic ground wave to the sound source detection of the near-ocean-bottom target,which shows that the joint detection system of the VLF acoustics and seismic waves has a certain application prospect.