Research On The Spatial Correlation Of The Acoustic Vector Field For Surface-generated Noise In Shallow Water

Signal-to-noise ratio output of a hydrophone array is much more depending on the spatial correlation structure of the noise field. As for the performance analysis of an acoustic vector hydrophone array, it is very necessary to know the spatial correlation characteristics, not only for sound pressure, but also for acoustic particle velocity. Comparing among the presented models of the spatial coherence of sound pressure for surface-generated noise, two models which will be used to do the research of spatial correlation of the acoustic vector field in horizontally stratified media are introduced. One is the normal-mode model developed by Kuperman, and the other is the geometric model developed by Harrison.In order to verify the validation of the models extending into the acoustic vector field, the surface-generated noise in a semi-infinite space is firstly modeled. Using Euler's formulation between sound pressure and particle velocity, corresponding quantities of the acoustic vector field are obtained. Based on the geometric model, analytical expressions of the correlation coefficients which are the same as those given by Huang are given. Except for that, sound pressure is formulated in the Green's function and the normal-mode method is introduced. Similar to the derivation of the particle velocity of the above, identical coefficients of the acoustic vector field are also been given. This shows the feasibility of the method presented in the thesis and it will be used in the following study of the surface noise in an idealized channel.With the theoretical foundation of the above, research of the spatial correlation of the surface noise in a horizontally stratified media becomes much more explicitly. Step by step, a surface noise model in an idealized channel is constructed, consisting of homogeneous water column, rigid bottom and perfectly free surface. Similar to the simple model analysis, spatial correlation expressions of the acoustic vector field of the noise have been presented with the geometric model and the normal-mode model. Numeric calculations of the coefficients give a good agreement under the condition of high frequency or far field. This is for the plane wave hypothesis in the geometric model. From the results we can see that spatial structure of the ocean ambient noise not only depends on the directivity of the source, but also relates to the acoustic parameters of the ocean. The latter will be more meaningful for us in the prediction of the bottom.