Research About Modeling And Application Vertical Direction Characteristics Of Ocean Ambient Noise

The sufficient perception of the spatial characteristics of ambient noise field in vertical direction is significant for both the reasonable distribution of underwater acoustic equipments and the acquisition of ocean waveguide information.This paper researches on the modeling and application of the spatial characteristics of ambient noise in vertical direction,the sound pressure cross spectral density function of ambient noise between two points in vertical direction is deduced as a complement to the P/K model,and then this model is extended to vector field.A multipath structure extraction method using vertical velocity information of ambient noise is presented based on the vector ambient noise prediction models,and this method was applied to the research of stepwise geoacoustic parameters inversion with ambient noise.The specific research contents are as follows:1.Modeling and verification study on the spatial characteristics of vector ambient noise in vertical directionCompared with the fast field noise model,P/K model has the advantages of fast calculation speed and wide application range.However,this model fails when calculating the spatial characteristics in vertical direction,this paper deduced the analytic expression of the sound pressure cross spectral density function of ambient noise between two points in vertical direction,making the P/K model is available in spatial characteristics forecast in vertical direction,and extended the scalar model to the vector field,which provides theoretical basis for the application of vector noise field.Vertical coherence,vertical correlation and vertical directivity of ambient noise in hard bottom and soft bottom were simulated,by comparing those simulation results with fast field noise model forecast results,accuracy of the model presented in this paper is verified.The spatial characteristics of ambient noise in the continental shelf of the South China Sea is predicted using the P/K model,theoretical forecast results consistent well with the measured results.2.Modeling on the influence of sea surface fluctuation on the spatial characteristics of noise field in vertical direction.It is necessary to consider the effect of sea surface fluctuation on the medium-high frequency acoustic propagation in severe sea conditions.This paper presents a spatial characteristic prediction model of noise field in vertical direction which can consider the impact of fluctuation of sea surface based on the transport theory.By analyzing the influence of surface fluctuation on the intensity and phase of normal modes,the influence of surface fluctuation caused by severe sea conditions on the intensity distribution,vertical correlation and vertical directivity of ambient noise were analyzed.Simulation results show that the surface fluctuation not only can reduces the noise intensity and the wave intensity propagate near critical angle,but also can reduce the vertical correlation of ambient noise.3.Research on the multipath structure extraction using vertical velocity signal of ocean ambient noiseBased on the spatial characteristics forecast model of vector ambient noise in vertical direction,a multipath structure extraction method using vertical velocity signal of ocean ambient noise is presented,which can extract the multipath structure between two vertical separated points rapidly and suppress the nonphysical arrival structure such as spurious head wave.Experimental data processing results show that the signal length required for multipath structure extraction can be greatly shorten using vertical vibrating velocity signal of ambient noise.4.Research on the stepwise geoacoustic inversion using the coherence characteristic of ocean ambient noise vector fieldTaking advantage of the excellent performance of vertical vibrating velocity hydrophone in bottom layer structure acquisition and the geoacoustic parameters inversion,this paper researches on the stepwise geoacoustic parameters inversion using the vector signal of ocean ambient noise.Firstly,extract the multipath structure and acquire the bottom layered structure using vertical vibrating velocity signal of ambient noise,and then select corresponding seabed model,finally,the bottom parameters inversion is performed with the vertical coherence function of vertical vibrating velocity of ambient noise.The performances of geoacoustic inversion by using sound pressure coherent function and vertical vibration velocity coherent function are compared,results show that vertical vibration velocity coherent function is more sensitive to the bottom sound speed than sound pressure coherent function,better performance in bottom speed inversion can be acquired by using vertical vibration velocity field information of ambient noise.The research in this paper provides theoretical basis for the application of the vector noise,providing a new path for the multipath structure extraction and geoacoustic parameters inversion at low SNR.The work has certain theoretical value and application prospect.