Research On The Characteristics And Positioning Of VLF Vector Sound Field In Shallow Sea Environment

With the rapid development of mute technology,the radiated noise level of ships and submarines has been greatly suppressed in the middle and high frequency bands,and even low-frequency signals are not only difficult to eliminate,but also form a seabed seismic wave field after coupling with the seabed.The form spreads far away,so the research on VLF acoustic signals has important practical significance.This paper mainly studies VLF vector sound field,seismic wave field and sound source azimuth estimation methods.The thesis studies the generation mechanism of the VLF signal radiated by the underwater vehicle.According to the dynamic equation of the underwater vehicle,the mechanism of the low-frequency radiation sound generated by the underwater vehicle is discussed,and the finite element software is used to analyze the low frequency of the underwater vehicle.Value oscillation is simulated,and the result shows that it can be regarded as a quadrupole sound source according to its sound field characteristics.Construct a ship seismic wave displacement field model in a rectangular coordinate system to analyze the influence of environmental parameters on the interface wave dispersion characteristics and the movement of particles at the interface.The experimental data is used to verify the elliptical polarization characteristics of the interface wave signal.The comparison verifies the effectiveness of COMSOL software for constructing the acoustic propagation model of the liquid seabed and the elastic seabed.Use COMSOL to build a very low frequency ground sound propagation model,and study the two-dimensional sound field model and interface displacement propagation loss under different acoustic parameters,and analyze the very low frequency sound propagation characteristics and influencing factors.The thesis studies the target horizontal distance estimation based on the time delay difference method,the improved sound intensity method based on the seabed seismograph,and the sound pressure matching field and vector matching field positioning methods.The robustness of the matching field is studied,and the effects of signal-to-noise ratio,grid division,environmental mismatch and array mismatch on the positioning performance of the matching field are analyzed.The vector matching field is used to process the Xin'anjiang test data,which verifies the effectiveness of the improved sound intensity method and the vector matching field algorithm.