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

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 max-imum 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.