深海海底山对声波的反射和阻挡效应

The reflection and shadow effects of seamounts on sound propagation in deep water

2014年在中国南海进行了一次深海海底山环境的声传播实验.本文利用宽带爆炸声信号分析了海底山对声传播的影响.在第一会聚区位置,由于海底山的阻挡,海底山环境下传播损失(TL)增加了30 dB以上.此外,实验观察到在第一影区的位置,由于海底山的反射,海底山环境下的传播损失比无海底山环境下的传播损失减小近7 dB.在28 km附近,海底山环境下的传播损失随着接收深度的增大而增大,接收深度170与1868 m处的传播损失相差近10 dB.在距离大于30 km时,不同接收深度条件下的声传播损失随距离的变化趋势基本一致,且大部分距离处的差异小于3 dB.实验得到的传播损失和脉冲达到结构与理论计算结果符合得很好,并利用射线和波动理论解释了由于海山引起的传播损失异常现象和脉冲到达结构.

The seamounts have enormous effects on sound propagation in deep water. Some abnormal propagation phenomena were observed for two different tracks with the flat bottom and the seamounts bottom environments. A propagation experiment was conducted in the South China Sea in 2014. The effects of seamounts on sound propagation were analyzed by using the wideband signals. It＇s observed that, in the first shadow zone about 28 km, the transmission loss （TL） for the environment with the seamounts was decreased up to 7 dB compared with the TL for the environment without the seamounts, due to the reflection effects of the seamount. And in the first convergence zone about 56 km, the TL was increased more than 30 dB for the shallow source. It was because that most of the deep refraction waves were blocked by the seamount. In the reflection zone of seamount, the TL increased as the depth of the receiver became deeper for less of sound rays could arrival and most of the grazing angles became bigger. Moreover, the TL difference between receiver depth 170 and 1868 m was nearly 10 dB. At the range more than 30 km, the TL trends were consistent as receiver depth vary from 170 to 1868 m, because it can be equivalent to that all the rays were reject from the top of the seamount. The numerical TLs and pulse arrival structures can match with experimental results well. Abnormal TLs and pulse arrival structures at different ranges are explained by using ray and wave theory.