浅海海底模型对低频声传播的影响

Effects of seabed model on low frequency sound propagation in shallow water

海底参数特性是影响浅海低频水声传播的重要因素。理论上需要知道海底所有深度的参数特性才能确定水声传播,这在实践中很不现实。如果在误差的允许范围内只需要知道某个深度以上的海底参数特性,而这个深度以下的海底参数特性可以忽略,这个深度就定义为海底最大深度。低频声波能够穿透海底更深,最大深度能够达到几十米深,对比较高频率只有几米深。海水声速剖面也能影响声波穿透海底深度,声速剖面为负梯度时海底最大深度比等声速要深。在低频声传播过程中,海底横波对声场影响也很大,尤其是在超低频100Hz以下,2002年5月的南海试验也证实了这一点。

Characteristics of seabed are important factors that affect low frequency propagation in shallow water. In principle, it is required to know the physical parameters at all depths in the seabed material, but this is not practical. If knowledge of the characteristics above certain depth is enough to constrain errors, characteristics of below this depth can thus be neglected. The critical depth may be viewed as the maximum depth. Low frequency sounds can penetrate seabed as deep as several tens of meters, while relative high frequency sound only several meters. Therefore, the sound speed profile （SSP） of sea also affects the maximum depth of sound penetration, and the maximum depth is greater in the downward refracting of SSP than in the uniform region of SSP. Shear wave is another factor affecting low frequency propagation in shallow water, especially below 100Hz, which is validated by the acoustic experiment of May 2002 on the south sea of China.