孤立内波对过渡海域声场干涉结构的影响分析

Influence of internal solitary waves on the interference structure of acoustic field in the continental slope area

南海北部陆坡海域是孤立内波的活跃区,孤立内波在该海域能够引起水体环境较强烈的水平不均匀性,从而影响声场干涉结构。将描述宽带声信号强度干涉条纹斜率的波导不变量视为一种分布,能更准确地分析声场的距离-频率干涉结构。本文研究了孤立内波环境下过渡海域声场的距离-频率干涉结构,依据实测孤立内波海洋环境,得到孤立内波环境下随距离变化的声速剖面,利用抛物方程方法仿真过渡海域声场干涉结构。在此基础上,利用拉东变换和傅里叶变换结合的谱值分离方法在低信噪比环境下提取波导不变量分布。分析表明孤立内波环境下过渡海域的声场类影区、类会聚区的波导不变量取值更丰富。

Isolated internal waves are active in the northern Nanhai Sea.Obvious horizontal heterogeneity of sea sound velocity can arise in isolated internal waves environment,which affects the interference structure of sound field.Waveguide invariant can be used to describe the interference fringes of broadband acoustic field intensity.It is taken as a kind of distribution to analyze the slope of interference fringes of sound field.In this paper,the distance-frequency interference structure of sound field is studied in an internal solitary wave environment.Firstly,the sound velocity profile of internal solitary wave environment is obtained according to the measured data.Then,the sound field is numerically simulated by parabolic equation method,and the distance-frequency interference structure of sound field is constructed.Taking advantage of Radon transform and Fourier transform,the distribution of waveguide invariant is extracted from ambient noise.It is shown that the waveguide invariant is more complex in the shadow zone and convergence zone when isolated internal wave exists.