极浅水环境中水体深度对水底混响强度的影响分析
Influence of waveguide depth on bottom reverberation strength in very shallow water environments
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摘要: 相对浅水环境, 极浅水环境易产生更强的水底混响, 不利于水下慢速小目标探测。针对该问题, 从水体深度的角度分析了极浅水强水底混响的成因和条件。首先, 建立了高频声能量的多途传播和水底散射模型; 其次, 量化分析了水体深度对多途到达结构和水底散射强度的影响; 最后, 归纳出水体深度对水底混响强度的作用传递关系。定义脉宽内多途强度累积值衡量水底混响强度, 令其等于脉宽内多途数和脉宽内多途平均强度的乘积。以中砂和粗泥底质类型为例, 利用数值仿真验证了理论推导结论。结果表明: 底质为粗泥时, 极浅水环境的多途平均强度显著低于浅水环境, 而多途数略高于浅水环境, 因此多途平均强度对水底混响强度的作用占主导地位, 导致极浅水混响强度低于浅水; 底质为中砂时, 极浅水环境的多途平均强度略低于浅水环境, 而多途数显著高于浅水环境, 因此多途数对水底混响强度的作用占主导地位, 导致极浅水混响强度高于浅水。Abstract: In comparison with the shallow water environment, the very shallow water environment is more likely to generate stronger bottom reverberation, which hinders the detection for the underwater low-speed small target. To solve this problem, the mechanism and the conditions of the stronger bottom reverberation in very shallow water are analyzed in detail from the perspective of the waveguide depth. Firstly, the multipath propagation model and the bottom scattering model for underwater high-frequency acoustical energy are established. Then, the influence of the waveguide depth on the multipath structure and the bottom scattering strength are analyzed quantitively. Finally, the influence mechanism of the waveguide depth on the bottom reverberation strength is summarized. In this paper, the accumulated value of the multipath strength during a pulse width is defined to measure the bottom reverberation strength, which is the product of the number of multipath during a pulse width (NMPW) and the average strength of multipath during a pulse width (ASMPW). Taking the medium sand and the coarse silt as examples, the theoretical results are verified through numerical simulations. In terms of the coarse silt sediment, ASMPW in very shallow water is significantly lower than that in shallow water, but NMPW in very shallow water is slightly higher than that in shallow water. The ASMPW plays the dominant role in bottom reverberation strength, hence very shallow water shows no stronger bottom reverberation than shallow water. In terms of the medium sand sediment, ASMPW in very shallow water is slightly lower than that in shallow water, but NMPW in very shallow water is significantly higher than that in shallow water. The NMPW plays the dominant role in bottom reverberation strength, hence very shallow water shows stronger bottom reverberation than shallow water.