The effects of sediment porosity on acoustic reflection and transmission at the seafloor

Abstract

(Manu2OThe Biot theory of propagation in a porous medium provides a mathematical framwork for studying acoustic interaction with the seafloor. The theory considers the two-phase porous nature of marine sediments in contrast to the classical models of wave propagation in the seafloor that consider marine sediments as an extended single-phase fluid or solid.A boundary value problem is set up and olved for a line source in a fluid medium above a ooro-vi r'oelastic halfspace. Expressions for the reflected nd transmitted field are given in integral form and asymptotic expansions in the high-frequency, far-field limit.A set of simultaneous equations is solved to give plane wave reflection and transmission (Type I, Type II and shear wave) coefficients.These equations also yield the Scholte, pseudo-Scholte and pseudo-Rayleigh wave phase velocities and attenuations.The plan wave coefficien and the surface wave velocities and attenuations are compared with commensurate quantities from the single-phase theories.A number of recent experiments of high frequency transmission through a water-sand interface have indicated anomalously high transmitted energy at angles near the critical angle. The Type II wave (predicted by Blot theory but not the single-phase theories) was suspected as a possible reason for the anomalies.Data from one of the experiments are examined sediment porosity, seafloor, reflection, transmission, porous medium, acoustic interaction, two-phase, water-sand interface, Biot theory