【作者】 李丙辉；

【导师】 李琪；

【作者基本信息】 中国海洋大学 ， 声学， 2004， 硕士

【摘要】 浅海海洋环境下，环境噪声源发出的声波在传播过程中在海面与海底之间经历多次反射。海洋环境噪声场即是由大量噪声源及其各自的声场与环境边界的相互作用共同决定的一种随机过程。由于这种多途相互作用，时间平均的环境噪声场体现出由环境条件决定的空间结构。浅海海洋环境下，噪声场的空间结构很大程度上由海底特性决定。作为水声信道的一种背景干扰场，海洋环境噪声场的空间结构特性是影响水声系统的主要因素之一。同时，海洋环境噪声又是有用的信号，可以用其空间结构来对海洋环境参数进行反演。在噪声场诸多特性当中，垂直指向性与垂直相干特性相对稳定，可以充分反映噪声场的空间结构。本论文基于水平分层浅海风成海洋环境噪声场模型，对噪声场垂直指向性、垂直相干特性以及利用垂直相干反演海底参数问题作以研究。其中，在计算噪声场互谱密度时，采用简正波求和形式，这样不仅可以用模式图像的物理意义直接解释噪声问题，而且可以利用绝热模式理论把噪声表达式扩展成与距离有关的环境。但是若仅考虑离散简正波场的求和，将会丢失掉环境噪声问题中对场有重要贡献的连续谱。为将这一部分考虑在内，在海底某深度引入一虚假深海底，用复模式之和去近似计算分支割线的积分。论文首先讨论了不同海面噪声源面积与指向性图案、不同海水声速剖面、不同海底类型、不同接收器布设以及不同频率的情况下，噪声场的垂直指向特性。然后，分析了各环境参数与噪声场垂直相干的关系，包括海底各参数、海面噪声源深度、海水声速剖面、两接收点深度和间距等因素对垂直相干的影响。在此基础上，通过数值模拟，利用噪声场的垂直相干的“观察值”与“计算值”相匹配的方法来对海底地声参数进行反演，并作反演结果的后验概率分析。其中，将遗传算法作为反演过程的搜索算法。通过这几部分的工作，可以得出以下结论： 1．噪声场的垂直指向性能够充分反映噪声场中波导的基本传播特性。各环境参数如海面源面积和源指向性、海水声速剖面、海底类型等对声传播的影响，以及对噪声场有贡献的连续谱域与离散谱域，都可以在噪声场的指向性中得到直观的体现。但是，若想利用垂直线列阵获得较好的指向性效果，浅海风成海洋环境噪声场空间结构及海底参数反演研究 则需增加垂直线列阵的阵长及水听器间距。2.噪声场各环境参数中，海面噪声源深度以及海底各地声参数(尤其是纵波 声速、横波声速与沉积层厚度)与噪声场两接收点垂直相干特性的依存关 系明显不同，因此，可以考虑利用噪声场的垂直相干的“观察值”与“计 算值”相匹配的方法来对海底地声参数进行反演。3.用噪声场垂直相干反演海底参数，并将遗传算法作为反演过程的搜索算法。 计算结果表明，理想环境条件下，反演结果可以精确收敛于参数的“真实 值”;有干扰的情况下，各参数反演结果的不确定性与噪声场垂直相干对参 数的灵敏程度基本对应。这证明了反演方法及搜索算法的有效性。4.实际海洋环境复杂多变，噪声源、海底，甚至海水声速剖面都可能与距离 有关。因此，为更为深入认识噪声场特性及利用环境噪声场反演环境参数， 需要进一步建立更为符合实际海洋环境的与距离有关的海洋环境噪声场模 型。更多还原

【Abstract】 In shallow water, Sound emanating from a noise source undergoes multiple reflections between the sea surface and sea floor. The ocean ambient noise field is a stochastic process of many such noise sources and the respective interactions of their wave fields with the environmental boundaries. As a consequence of the multi-path interaction, the time-averaged ambient noise exhibits spatial structure that is determined by the environmental parameters. Especially in shallow water, the spatial structure is largely determined by the characteristic of seabed. The ambient noise field is one of interference fiend of underwater sound-channel, its spatial structure is one of major factors affecting the performance of underwater sound systems. And furthermore, the ambient noise field is useful information. Some environmental parameters can be inversed by its spatial structure. As relative stable characteristics, vertical directionality and vertical coherence of ambient noise field can exhibit sufficiently the spatial structure of ambient noise field. In this thesis, the vertical directionality, the vertical coherence and the inversion of seabed parameters using vertical coherence are studied based on the range-independent wind-generated ocean ambient noise model in shallow water. When calculating the cross-spectral density of ambient noise field, the normal-mode representation is used. This can not only directly explain the noise problem by the physical map of modes, but expand the noise expression to the case of range-dependence. The part of continuous spectra, which greatly contributes to the noise field, will be lost when the part of discrete normal modes is considered only. To include this part, an artificial layer is added at a certain depth in the bottom. The integration of branch cut is approximately calculated by the summation of the complex modes. Firstly, the vertical directionality of ambient noise field is discussed under different environmental conditions, such as the area of surface noise sources, source directional pattern, sound speed profile, bottom type, the design and placement of receivers and frequency. Secondly, the relations between environmental parameters and vertical coherence are analyzed, including on vertical coherence the effects of bottom, noise source depth, sound speed profile, depths and interval of two receivers. Finally, based on the discussions above, through numerical simulation, the bottom parameters are inversed by matching the "observed value" and "real value" of vertical coherence of ambient noise field and a posteriori probability distributions of the model parameters inversed are estimated. In the process of inversion, Genetic Algorithm is used. Through the works that have been done, the conclusions are drawn as follows: 1. The vertical directionality can exhibit sufficiently the characteristics of soundchannel in ambient noise field. The effects of environmental parameters, which including the area of surface noise sources, source directional pattern, sound speed profile, bottom type, the design and placement of receivers and frequency, on sound propagation and the discrete and continuous spectra of ambient noise field can be seen expressly through vertical directionality. In order to get better vertical directionality, the length of the vertical linear array and intervals of hydrophones should be increased.2.Among the environmental parameters of ambient noise field, noise source depth and the geo-acoustic parameters affect the vertical coherence in different ways, especially compressional speed, shear speed and depth of sediment do. So it can be considered to inverse seabed parameters by matching the "computing value" and "observed value" of vertical coherence.3.The results of numerical simulation shows that the parameters inversed converge on their "real value" in ideal environmental condition and the uncertainty of each parameters inversed agrees with the sensitivity of corresponding parameters to the vertical coherence when there has low -frequency disturbance. This更多还原