负梯度水文环境下海山对声传播的影响

The effects of seamount on sound propagation in the negative gradient sound speed environment

利用一次南海海山环境下的声传播实验数据,研究了负梯度水文环境下海底山对声传播的影响。针对实验数据中的传播损失异常,从射线声学角度给出了合理的解释,表明海底山的存在引起传播损失在距离上剧烈波动。在距离接收阵较近的7.6 km处,声源位于海山斜坡上,斜坡的反射使接收传播损失减小约8 dB,体现出斜坡增强特征。当声源位于海山后,海底山的遮蔽作用使23.8 km处的传播损失增加超过20 dB,不同位置处海山遮蔽效应的差异使传播损失随距离起伏。利用抛物模型对实验环境下的声传播进行了定量仿真,仿真传播损失同实验结果符合,验证了实验数据中海底山的反射和遮蔽作用。此外,对实验环境下海山的遮蔽损失进行分析,发现在不同声源位置处,海山遮蔽损失在特定频带上同频率对数具有线性关系。

Based on the experiment data collected in the South China Sea in 2015,the effects of seamounts on sound propagation with negative gradient sound speed profiles are studied.Reasonable interpretations are given for the observed anomalies in Transmission Losses(TLs)in terms of acoustic ray propagation,demonstrating that the existence of a seamount in propagation direction leads to the fluctuations of TLs with respect to range.When the source is near the Vertical Line Array(VLA)at 7.6 km,rightly on the slope of the seamount,8 dB decease of TLs is observed for the slope reflection,confirming a similar mechanism of enhancement of down-slope in SOFAR channel waveguide.When sources are launched over the seamount,the seamount shadowing leads to more than 20 dB increase of TLs at 23.8 km and fluctuations at specific spots for differences of acoustic shadowing.Furthermore,quantitative numerical simulations based on the experiment environment are also performed by the parabolic equation model.The simulated TLs at several receiving depths show good accordance with the experiment data,which verifies the effects of reflection and shadowing of the seamount.In addition,the analyses of acoustic shadowing losses at different source positions reveal a linear relationship between shadowing losses and the logarithm of frequencies at specific frequency band.