岛礁区域斜坡地形对深海环境噪声级深度分布的影响

考虑岛礁区域斜坡地形的影响,从理论上分析了南海深海区域噪声级随深度增加而变大的现象。南海北部深海区域环境噪声测量实验表明:大部分时间内噪声谱级随深度变化较小(160～800 m),但是在一些时间里,噪声谱级会出现随深度增加而变大的现象。考虑南海岛礁区域斜坡地形对声传播的影响,建立了南海深海区域的环境噪声模型,当航船经过岛礁附近时,航船噪声由于岛礁附近斜坡地形的作用进入深海声道,使远距离噪声谱级随深度增加而变大。利用模型计算噪声谱级随深度的分布,结果与实验数据符合较好。验证了南海深海区域噪声在岛礁斜坡地形影响下的复杂的变化特性。

海面波浪对海洋环境噪声垂直空间相关性的影响

研究了由海浪谱导得的噪声源的相关函数对海洋环境噪声垂直空间相关性的影响。常用的海洋环境噪声空间相关性模型一般假设海面噪声源是非相关的,这种假设可以解释一些物理现象,但是与真实情况并不符合。考虑到风成噪声与海浪运动的相关性,引入海浪谱,得到噪声源的相关函数,利用Kuperman-Ingenito (K/I)噪声模型,计算海洋环境噪声的垂直相关性。通过仿真结果与实验数据对比可以看出,在高风速下,假设噪声源不相关时计算得到的噪声场垂直相关性与实验结果相差较大,而利用由海浪谱导得的噪声源的相关函数计算得到的噪声场的垂直相关性与实验结果符合较好。

Analysis on spatial difference of ocean ambient noise spectrum in the northern South China Sea

To study the spatial difference of ocean ambient noise in offshore China and reveal its generation mechanism, the difference between the noise level(NL) of two stations is compared based on long-term observation data collected in the same season. Considering the influence of underwater acoustic channels and the characteristics of noise sources, the transmission loss level(TL) from the port ship noise sources to the measuring station is analyzed and it shows a strong correlation between the transmission loss difference(TLD) and noise level difference(NLD) at the band of 50-500 Hz. At the same time, the analysis of ship noise source level(SL) presents a difference about 20 dB between the two ports, corresponding to the variation of the ship density before and during the fishing moratorium. The results prove that the ambient noise is closely related to ship noise sources at this frequency band, and the noise difference between the two stations results from the transmission loss and the ship noise sources.

The effect of slope of island reef on the deep sea ambient noise

Considering the effect of the slope of reef area,the phenomenon that the noise level in the deep sea area of the South China Sea increases with depth is analyzed theoretically.The experiment on ambient noise in the deep sea area of the northern South China Sea shows that the noise spectrum level changes little with depth(160 m to 800 m) for most of the time,but at some time,the phenomenon that the noise spectrum level increases with depth would arise.Considering the effect of topography on sound propagation in the South China Sea,the ambient noise model of deep sea area in the South China Sea is developed.When a ship passes the sea around the reef or island,the ship noise spreads into the deep sea sound channel due to the terrain near the reef or island such that the distant noise spectrum level increases with depth.The distribution of noise spectrum level with depth can be computed by using the noise model,and it has good agreement with the experimental data.So the variation characteristics of deep sea noise affected by the slope of island reef in the South China Sea are verified.

The effect of ocean wave on the vertical spatial correlation of ocean ambient noise

The effect of the correlation function of noise sources derived from the ocean wave spectrum on the vertical spatial correlation of ocean ambient noise is investigated. The spatial correlation models of ocean ambient noise usually assume that the surface noise sources are uncorrelated. This assumption can be used to explain some physical phenomena, but it is not consistent with the real situation. Considering the relation between the ocean wave motion and the ambient noise generated by wind, the spectrum of ocean wave is introduced to calculate the vertical correlation of ocean ambient noise as the correlation function of noise sources by using the Kuperman-Ingenito （K/I） noise model. The comparison of the simulations and the experimental data shows that the simulations of vertical correlation of ambient noise have some differences with the experimental data by assuming the noise sources are uncorrelated and the simulations of vertical correlation of ambient noise have a good agreement with the experimental data by using the correlation function of noise sources derived from the ocean wave spectrum under the situation of high wind speed.