Researches On Structural Characteristics Of The Sound Intensity Vector And Source Depth Discrimination In Shallow Water

Deepening the understanding of vector sound field characteristics is of great significance for sound source target detection in shallow water.Most of the current research on sound source depth discrimination is based on scalar sound pressure signal processing,but the research on the vector characteristics of the sound field itself is not enough.The vector sound field contains rich sound source and channel information.The structural features of the sound intensity vector help to extract the key sound source location information and provide new ideas for sound source target detection.This paper first studies the vector sound field characteristics in shallow water,and then explores the method for sound source depth discrimination based on the vector sound field characteristics and single-vector hydrophone.The main work of this thesis includes:(1)The distribution characteristics of particle motion trajectories in the sound field are studied.The circularity degree is used to represent the particle motion trajectory of the vertical plane of the sound field,and its spatial and space-frequency interference characteristics are analyzed.Theoretical analysis and simulation results show that the circularity degree has a regular interference structure in space,and its distribution is related to the depth and the frequency of the sound source.There are clear interference fringes in the space-frequency interference of the circularity degree,and the fringe slope can be characterized by the waveguide invariant theory.The sign distribution of the circularity degree is consistent with the vertical complex sound intensity reactive component.(2)The structural characteristics of the sound intensity vector vortex are studied.Theoretical analysis and simulation results show that when there are only two-order normal waves in the sound field and the amplitudes of the first-and second-order modals are equal,the center point of the sound field vortex will appear at a certain distance,and then a vortex region will be generated.When there are two-order modes in the sound field,the depth of the sound source directly determines the existence of the vortex.When there is multi-order modal interference,the depth of the sound source affects the position and structure of the vortex.The motion trajectories of particles in the vortex region also show different characteristics.The sign of the circularity degree changes in the vortex region and an extreme point appears,this feature can be used for the identification of the vortex region.(3)Based on the single-vector hydrophone and vector sound field,three methods for depth discrimination of motion sound sources are explored in shallow water.For very low frequency sound sources,the sound source depth interval is divided according to the distribution difference of particle motion trajectory features.For a waveguide environment with a negative cline sound speed profile,the surface and underwater targets can be distinguished by the position of the vector wavenumber spectrum.Finally,for a short-range sound source with a nearest passing point,a motion model is established that uses radial velocity to discriminate the depth of the target.The research in this thesis shows that the vector sound field contains rich channel and target sound source information,and the change of the sound source depth will change the structural characteristics of the sound intensity vector,which can provide a new idea for the sound source depth discrimination.The motion sound source can solve the problem of insufficient spatial sampling of the single-vector hydrophone,and the depth of the sound source can be discriminated by combining the vector characteristics of the sound field.