Research On The Sound Field And Correlation Of Target Scattering In Shallow Water Channel

The scattered echo of a target is one of the most important information for detecting,tracking,locating and identifying targets in a shallow sea.However,the research on the distortion of randomly rough sea surface scattering on the sound field scattered by the target in the shallow ocean waveguide is still an open question.The total scattered field is decomposed into a decisive(ensemble)average and a stochastic parts.The effects of the different attenuation rate of modes of the average field,which is produced by the scattering of the randomly rough surface,on the spatial correlation of the multi-modal(multi-path)average field are studied.The effects of the mode coupling by random scattering on the sea surface and the mode coupling by spherical scattering on the stochastic fields are theoretically studied and numerically calculated.These stochastic fields include: 1)The average field of a point source is "incident" to the randomly rough sea surface,the stochastic field is formed at the randomly rough sea surface and then propagate directly to the receiving point.2)The average field of a point source is "incident" to the randomly rough sea surface,and stochastic field is formed at the randomly rough sea surface and then propagate to the receiving point after being scattered by the sphere.3)The average field of the point source is “incident” on the randomly rough sea surface after being scattered by the sphere,and the stochastic field is formed at the randomly rough sea surface and then propagate to the receiving point.4)The average field of the point source is “incident” on the randomly rough sea surface after being scattered by the sphere,and the stochastic field is formed at the randomly rough sea surface and then is scattered by the sphere,and propagate to the receiving point.The spatial correlation function is directly expressed as functions of the power spectrum of the randomly fluctuating sea surface,the coupling of modes caused by spherical scattering and the coupling of modes caused by random sea surfaces.The Monte Carlo numerical simulation is avoided,and the calculation efficiency is greatly improved.The physical image is clearer.The results of theoretical study and numerical calculation show that the scattering attenuation in the far field will increase the horizontal and vertical correlation of the average field.Due to the symmetry of mode scattering,the scattering of the sphere has little effect on the correlation of the average field.Theoretical studies show that the distortion of the scattered wave of the sphere in the shallow water waveguide by the randomly rough sea surface scattering may be expressed as the product of the spherical scattering matrix and the random sea surface scattering matrix,and the random sea surface scattering matrix may be expressed as the power spectrum of the sea surface.Through an example of sea surface power spectrum which is constructed by the superposition of two sine waves with random phases,it is shown clearly that the power spectrum of the sea surface(the wave number spectrum or period of the sine sea surface)has a significant modifications on the mode structures of the spherical scattering field in the waveguide.