Reflections and transmissions from a porous layer sandwiched between seawater and solid substrate

Ocean sediments are composed of a porous layer sandwiched between seawater and a solid elastic base. The reflection and transmission of acoustic waves from ocean sediments are essential in ocean engineering, seafloor seismology, etc. The existing reflection and transmission (R/T) formulas are determined by complex matrix equations in the order of 9 x 9 or higher. To obtain more concise R/T coefficient formulas, we established the propagator matrix of the coupled water-porous-layer-solid elastic system, wherein the above-water is ideal and the middle porous marine sediment is defined by the Biot-Stoll model. Based on the propagator matrix, the displacement R/T coefficients were given by a 3 x 3 matrix equation for two P-wave incidence cases: the down -going case from the water, and the up-going case from the ocean floor. For zero-frequency or zero-thickness limitation, the proposed R/T coefficient formulas are the same as the displacement R/T coefficients at a single fluid-solid interface. The numerical results of the reflected or transmitted waves in the above-water show that the R/T coefficients exhibit regular variations at frequencies far lower than the characteristic frequency. The R/T coefficient amplitudes decreased with increasing frequency at a fixed incidence angle and ratio between the thickness and wavelength.

Automated summary

This article studies the reflection and transmission of acoustic waves in ocean sediments and proposes a more concise formula for the reflection and transmission coefficients. By establishing the propagator matrix of the coupled water-porous-layer-solid elastic system, the method for calculating the displacement reflection and transmission coefficients for P-wave incidence cases is provided.