【作者】 郭国强；

【导师】 孙超；

【作者基本信息】 西北工业大学 ， 信号与信息处理， 2007， 硕士

【摘要】 浅海波导中，混响是限制主动声纳作用距离和系统性能的主要背景干扰。它不仅和发射信号本身有着密切的关系，而且还和传播通道的特性有关，故混响的抑制一直是一个具有挑战性的难题。时间反转处理方法利用了静态介质中波传播的相互性，可以在不均匀的声学介质中实现声束的聚焦，而不需要介质和换能器阵列性质和结构的先验知识。这为目标回波增强和海底混响抑制提供了新的思路和方法：通过时间反转处理将声能量聚焦到目标位置，从而有效地增强目标的回波，同时抑制聚焦点上下的界面混响。本文主要研究了时反处理在混响抑制方面的应用，内容包括： 1．讨论了海洋混响的基本理论和混响的射线-简正波模型。利用简正波理论推导出了本地海底混响平均强度的计算公式。 2．研究了时反处理的基本原理及其空间和时间聚焦特性。通过计算机仿真实验，研究了时反处理在浅海波导中的实现(时间反转镜)。 3．研究了迭代时反处理和时反算子分解方法。利用传输矩阵分析了迭代时反处理的收敛性和时反算子分解方法的原理。并在不同条件下，仿真分析了两种方法的选择性聚焦能力。 4．研究了时反处理在增强信混比方面的应用。分析了典型浅海波导环境中时反处理增强信混比的能力和性能，以及时反处理对两次传输过程中环境变化的稳健性。进一步将时反阵推广到一般激励情况，给出了时反零点设置方法。最后，结合时反聚焦和时反零点设置原理，给出了一种混响零点约束的回波增强方法。 5．研究了一种基于时反算子分解(DORT)的混响凹槽设置技术。在没有探测声源的条件下，通过对接收的混响信号进行时反算子分解处理，可以获得海底混响的聚焦和置零权向量。通过计算机仿真，分析了波导中不存在目标和存在目标时，混响凹槽设置方法的性能和缺陷。针对波导中存在目标时，该处理方法在相应距离的海底设置混响凹槽的同时也会在目标位置设置凹槽的问题，提出了一种新的SRA加权向量的选择方法，实现了时反处理产生的声场在海底设置零点的同时在目标处聚焦，从而进一步增强了接收端的信混比。更多还原

【Abstract】 In shallow water, reverberation is the prominent interference to active sonars, which constrains the range and system performance severely. Reverberation is produced by the sonar itself, and it is also related to the character of transmission channel. So the suppression of reverberation is always a difficult problem. Time reversal is a process that utilizes the reciprocity of wave transmission in static medium and can focus acoustic energy at origin of the probe signal, without the knowledge of medium and transducer array. So it provides a new method to echo enhancement and reverberation suppression: Time reversal processing can be utilized to focuses acoustic energy on target, thereby resulting in the enhancement of target echo and the reduction of reverberation form the boundaries. This dissertation studies the application of time reversal processing in reverberation suppression. The following are the main contents of the dissertation:1. The ocean reverberation theory and the ray-normal mode reverberation model are discussed. The formula for average intensity of ocean bottom reverberation is deduced on the basis of normal mode theory for monostatic case.2. The principle of the time reversal processing and its spatial and time focusing are studied. Then the realization of time reversal processing in shallow water (Time Reversal Mirror) and its focal properity are analysed via computer simulation.3. The iterative time reversal processing and the decomposition time reversal operator method are studied. The convergence of the iterative time reversal processing and the principle of the decomposition time reversal operator are analyzed theoretically by transfer matrix. Then their selective focusing capabilities are analyzed via computer simulation.4. The application of time reversal processing in echo-reverberation ratio enhancement is studied. Firstly, the capability and the stability of time reversal processing for echo-reverberation ratio enhancement are studied by computer simulation in shallow water. Then the time reversal nulling method is given by extending the source and receiver array to normal excitation weight vector. Lastly, a new time reversal processing approach with constraints of reverberation null for echo enhancement is proposed, combining the time reversal focusing and nulling.更多还原