A study of reflection loss. II. Involving a porous layer and a demonstration of the Biot slow wave

As part of a study of the effects of porosity on reflectivity a seabed comprising a single porous layer overlying a solid half-space is examined and numerical calculations are made for versions of this model. It is shown that at very low frequencies the reflection coefficient for such a structure lies very close to that for the solid basement, while at high frequencies it tends to that for a porous half-space. At intermediate frequencies a transition band is identified in which the reflection coefficient is influenced by interference of the modes of the three Biot’s waves, the fast compressional and shear waves being dominant in most cases. In a simulation of a recent experiment the pressure field inside a sand layer is calculated and compared with the experimental results. The comparison supports the claim made by the authors that they had provided the first experimental demonstration of the existence of the Biot slow wave.