【作者】 高博；

【导师】 杨士莪；

【作者基本信息】 哈尔滨工程大学 ， 水声工程， 2013， 博士

【摘要】 浅海低频远程海底混响的研究由来已久，然而随着水声技术的不断拓展，尤其是未来的低频强声主动拖曳探测系统，或者近岸多基地主动探测系统欲实现对目标的远程探测，就迫切需要对浅海域中的低频混响特性以及复杂波导界面的小掠射角散射过程有更加清晰、深入的机理性认识和分析。鉴于此，本文以浅海低频远程海底混响的理论建模与特性研究为核心，建立了一套完整的以物理散射机制为基础的耦合简正波混响模型，并将其扩展到与水平距离有关的倾斜波导环境中。探讨了浅海低频远程海底混响的强度衰减规律、空间分布特性及其相应的物理机理。与此同时，本文还开展了大量的浅海海底混响的测量工作，对理论建模和特性分析给予了有力支撑。在理论建模方面：1、根据耦合简正波算法的物理意义，将接收点处的混响场视为海底粗糙界面或者不均匀底质对声场各模态信号的耦合作用所致。利用耦合简正波的观点解释了复杂的海底界面与海底不均匀介质的散射过程。2、根据海底界面起伏规律或者不均匀底质的分布情况，直接求得海底混响场的表达式，借助傅里叶积分可以对任意信号形式的海底混响场进行求解。给出了随距离变化的水平波导中本地混响、异地混响强度的解析表达式。3、对于缓坡倾斜海底的过渡海区，利用绝热近似，通过水平射线-垂向简正波理论求解了过渡海区海底混响的水平因子，进而建立了与水平距离有关的波导环境中的混响理论。该模型理论严谨，适用性广，并可扩展至三维问题。在针对工程应用的混响特性研究方面：1、从最基础的混响强度特性入手，尤其针对过去研究较少的多基地混响进行了系统深入的机理性探究，对比了本地混响和异地混响的强度及其衰减规律的异同，并首次探讨了过渡海域中多基地海底混响的强度衰减规律，结果表明斜坡环境中的传播效应对远程混响衰减影响显著。2、文中将混响过程视作一种无源网络，从声传播的视角，充分考虑浅海信道的环境效应和传播特点，细致讨论了海底界面起伏以及海底底质参数对异地远程海底混响强度衰减规律的影响机制。3、应用耦合简正波混响模型，探讨了浅海远程海底混响的空间分布规律，分析了垂向、水平纵向、水平横向相关的时/空/频特性，并在合理近似的基础上，定量描述了其变化规律。研究结果表明，浅海远程海底混响水平横向相关要优于水平纵向相关，而垂向相关最差。4、细致揭示了浅海波导边界对远程混响空间分布特性的影响。在不同海况条件下，从粗糙海面散射引起的模态耦合角度，探讨了起伏海面对浅海远距离混响的影响机制。结果表明，浅海中虽然海底混响占据支配性影响，但是，起伏海面增强了浅海波导远程传播过程中的“滤模性能”，使得高阶模态更快的消逝掉，从而增强了远程海底混响的空间相关。在外场试验测量方面：选取我国黄海、南海等典型浅海海域，分别在09年、10年和11年开展了三次浅海海底混响专项测量实验，获取了大量宝贵的高质量浅海海底混响数据，对数据的处理结果验证了本文理论模型和特性分析结果的有效性和准确性。更多还原

【Abstract】 It had been long before the beginning for researches about low frequency distant bottomreverberation in shallow water. With the ever ceasing development of underwater acoustictechnology, more deeply analysis and understanding from the view of its physical mechanism,the long-range bottom reverberation characteristic and the complicated boundary scatteringprocess，is much more demanded for the design of low frequency active sonar or multi-staticsonar system, which would be available for long-range target detection.Therefore, this dissertation is focused on the analysis about physical mechanism andmodeling of the low frequency long-range bottom reverberation (LFLBR) in shallow water.Firstly, the coupled modes reverberation model based on physical scattering mechanism isintroduced, and is extended to range-dependent waveguide. Then, the decaying rule of thereverberation level (RL) and the space coherence of LFLBR are discussed systematically. Inaddition to the mentioned theoretical researches, much LFLBR measurement is carried out intypical shallow water such as the Yellow sea and the South China Sea. The validity of thetheoretical modeling and analysis is thoroughly confirmed by data processing.Ⅰ. Theoretical modeling work:1. The reverberation field received by hydrophones is considered as the interaction ofincident modes with rough boundary or volume in-homogeneities in bottom medium bymeans of coupled mode method, which can explain the complicate scattering process ofbottom medium.2. According to roughness spectrum of the boundary surface and distribution of thesediment in-homogeneities, the formula of bottom reverberation is derived directly. Then, theFourier integration is used for the reverberation calculation of impulsive source with anysignal spectrum. In addition, the analytical expressions of RL are presented for both mono-and bi-static situation in range-independent waveguide.3. While for the range-dependent waveguide with varying depth, the adiabatic modesolution is introduced to derive the mathematical expressions for horizontal factors in slopingenvironment. This approach can also be extended to handle3D problems, which gives resultsobeying principle of reciprocity in all cases.Ⅱ. The discussion of characteristics for engineering application1. Beginning with the reverberation intensity, the RL of the multi-static sonar, for whichlittle work had been done before, is demonstrated systematically. The difference between the mono-static and the bi-static system is compared. Moreover, the decaying rule of RL forbi-static case in range-dependent waveguide is studied. The investigation indicates that theinfluence of sea floor inclination on RL should be considered.2. In thesis, the reverberation process is represented as a linear system without secondarysources. The sound channel effect and properties of sound propagation in shallow water areconsidered during the discussion of the RL for bi-static case. At the same time, the detailedphysical mechanism of the rough interface and the effect of sediment in-homogeneities on RLare displayed respectively.3. The space coherence of LFLBR is summarized by the coupled mode reverberationmodel. The time/space/frequency properties of the vertical, longitudinal, and transversecorrelation coefficients are predicted all-sided. It is indicated that transverse correlation isgreater than the longitudinal correlation, and it is most uncorrelated in vertical space.4. The surface effect on the space coherence of LFLBR is manifested. The mechanism ofsea surface effect on LFLBR is pointed out by describing the transfer of energy betweendifferent modes. It is indicated that the propagation effect of the shallow water waveguide isaffected seriously by the irregular upper boundary. Hence, higher modes are attenuated morequickly, and that will increase its space coherence.Ⅲ. Series of bottom reverberation measurements in shallow water:Three sea experiments for the measurement of bottom reverberation were conducted in2009,2010and2011respectivly. A large amount of high quality measured data was collectedin selected area of the Yellow sea and the South China Sea. The validity of the modelpredicted results is confirmed by data processing.更多还原