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声散射是海洋声学的重要内容, 海底表面的不平整性形成的声散射是海洋中引起声传播起伏的原因之一. 针对海底表面粗糙度声散射问题, 建立了水平分层浅海波导中海底散射声场模型. 该模型将简正波理论与Lambert定律相结合. 基于该模型获得了散射声场声压的振幅与相位的统计分布, 并数值模拟了海底散射声场的强度及其空间相关系数, 实现了粗糙界面条件下海底散射声场预报, 揭示了散射声场空间特性随海底粗糙度的变化规律. 结果表明, 使用Lambert定律描述粗糙界面声散射时, 在海底粗糙度小于波长情况下, 随着空间距离的增大, 空间两个不同位置的散射声场的空间相关系数具有周期性振荡衰减的变化规律, 并且在垂直方向上, 振荡周期更大, 衰减更慢. 当粗糙度增大时, 水平和垂直相关系数振荡幅度逐渐增大, 水平相关系数振荡周期数逐渐减少, 在接收点逐渐靠近海底时, 垂直相关系数不再发生衰减, 这是海底声散射减弱的结果. 本文模型理论亦可推广到粗糙海面的声散射建模中. 对于非水平海底情况, 采用耦合简正波或绝热简正波理论进行声传播建模, 可以得到距离有关波导中粗糙界面的散射声场.Acoustic scattering is an important part of ocean acoustics, and the acoustic scattering caused by the unevenness of the seafloor surface is one of the reasons for the fluctuation of acoustic propagation in the ocean. In order to solve the acoustic scattering problem of sea bottom surface roughness, normal wave theory is used to model the acoustic field. To simplify the problem, Lambert’s law is used to establish the seafloor rough scattering model in horizontal layered shallow sea waveguides, and the scattering field is assumed to be isotropic in the horizontal direction. Based on this model, the amplitude distribution and the phase distribution of the scattered sound pressure are obtained, and the intensity of the scattered sound field and its spatial correlation coefficient are simulated numerically. The prediction of the scattered sound field under rough interface conditions is realized, and the variation of the spatial characteristics of the scattered sound field with the roughness of the seafloor is revealed. The results show that when Lambert’s law is used to describe the rough interface acoustic scattering and when the seafloor roughness is smaller than the wavelength, the spatial correlation coefficient of the scattered sound field at two different positions in space has a change rule of periodic oscillation attenuation with the increase of spatial distance, and in the vertical direction, the oscillation period is larger and the attenuation is slower. When the roughness increases, the oscillation amplitude of the horizontal and the vertical correlation coefficient gradually increase, the oscillation period of the horizontal correlation coefficient gradually decreases, and the vertical correlation coefficient no longer attenuates in the direction near the seafloor, which is the result of the weakening of the seafloor acoustic scattering. The model theory in this paper can also be extended to the acoustic scattering modeling of rough sea surface. For the case of non-horizontal seabed, the scattered sound field of the rough interface in the waveguide can be obtained by using coupled normal wave or adiabatic normal wave theory.
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