Abstract

The effect of volume inhomogeneities in the sea bottom upper layer (sediments) on the long-range sound propagation in shallow water is analyzed. The experimental basis for developing inhomogeneous bottom models are the data of 3D seismic survey on the spatial structure of sediments in the Kara Sea, where variations of ~10% in the average sound speed in the bottom are observed at ranges of ~1 km. The mode coupling due to bottom volume inhomogeneities is revealed within the normal mode approach. Coupled mode equations are derived not only for propagating modes but also for leaky modes and quasimodes; including these types of modes may be urgent in analysis of the waveguides where the sound speed in the bottom (c₁) is less or approximately equal to the sound speed in water (c). Numerical simulations show that the coupling between energy-carrying modes is maximum at c₁ ≈ c. Calculations of the attenuation of depth-averaged sound field intensity in a water layer, performed for the Kara Sea at ranges of up to 5 km, show that the mode coupling due to bottom volume inhomogeneities can be neglected, and the depth-averaged transmission loss can be calculated using the adiabatic approximation at frequencies below a few hundred hertz. When analyzing the depth-averaged intensity, the effects of mode coupling on bottom inhomogeneities can be observed only by implementing special conditions, for example, using mode arrays providing maximally pure (free of other modes) radiation of a specified mode.

中文翻译：

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海底声速不均匀性对浅水中声波传播的影响

摘要

分析了海底上层（沉积物）中的体积不均匀性对浅水中远距离声音传播的影响。建立不均匀底部模型的实验基础是对卡拉海沉积物空间结构的3D地震勘测数据，其中在1 km范围内观察到底部平均声速的〜10％变化。在正常模式方法中揭示了由于底部体积不均匀导致的模式耦合。耦合模式方程不仅针对传播模式，还针对泄漏模式和准模式。在波导管的分析中，包括底部类型（c ₁）小于或近似等于水中声速（c）。数值仿真表明，携带能量的模式之间的耦合是在最大Ç ₁ ≈ Ç。对于卡拉海在长达5 km的范围内进行的水层深度平均声场强度的衰减计算表明，可以忽略由于底部体积不均匀性引起的模式耦合，并且可以平均传播深度的损耗可以使用几百赫兹以下频率的绝热近似来计算。在分析深度平均强度时，只能通过执行特殊条件来观察模式耦合对底部不均匀性的影响，例如，使用提供指定模式最大纯净（无其他模式）辐射的模式阵列。