南海大陆坡海底对海洋环境噪声的影响

Impact of continental-slope bottom on ambient noise in the South China Sea

通过位于大陆坡上和深海处的两站点相同深度噪声实验数据,分析了大陆坡海域不同海底环境对海洋环境噪声的影响,并利用三维射线模型计算了不同海底条件下的噪声谱级和垂直指向性,进而研究了海底环境对环境噪声场的影响规律,数值仿真的噪声谱级和实验结果在绝对幅值和随频率变化趋势方面均符合较好。实验和仿真结果表明,由于大陆坡上坡方向的浅海环境不利于航船噪声远距离传播,因此大陆坡上站点的低频(300 Hz以下)噪声谱级较深海处更低;由于大陆坡海底底质较硬,海面高频风生噪声除了直达接收器外还可经海底反射后到达,因此大陆坡上站点的高频(1 kHz以上)噪声谱级较深海处高且随频率下降缓慢,导致大陆坡上和深海处的环境噪声谱级曲线随着频率增加会存在交叉现象。

The impact of continental-slope bottom on the ocean ambient noise is analyzed by using experimental noise data received from the same depth at two locations on the continental slope and in the deep water,respectively.The noise spectral level and vertical directivity under different bottom conditions are calculated using a three-dimensional ray model,and then the influence of the bottom environment on ambient noise field is studied.The numerically predicted noise spectral level agrees well with the experimental data in terms of absolute amplitude and frequency trend.The experimental data and simulation results show that,in the shallow area of the continental shelf,the waveguide is not conducive to long-distance propagation for ship noise,therefore the low frequency(below 300 Hz)noise level is lower than that in the deep area at the same depth.Meanwhile,due to the bottom with hard characteristics in the shallow area,the high frequency(above 1 kHz)noise from the sea surface can also reach the receiver after being reflected by the seabed in addition to directly reaching the receiver.Therefore,the high frequency noise level in the shallow area on the continental shelf is higher than that in the deep area,and decreases with frequency slower.As a result,there is a crossover phenomenon of the ambient noise spectral levels on the continental slope and at the deep water with the increase of frequency.