Reflection Of Acoustic Plane Wave Research Articles

Coherent reflection of acoustic plane wave from a rough seabed, with a random sediment layer overlying an elastic basement

The problem of coherent reflection of an acoustic plane wave from a rough seabed with a randomly inhomogeneous sediment layer overlying a uniform elastic basement is considered in this analysis. The randomness of the sound field is attributable to the roughness of the seabed and the sound-speed perturbation in the sediment layer, resulting in a joint rough surface and volume scattering problem. An approach based upon perturbation theory, combined with a derived Green's function for a slab bounded above and below by a fluid and an elastic half-space, respectively, is employed to obtain an analytic solution for the coherent field in the sediment layer. Furthermore, a boundary perturbation theory developed by Kuperman and Schmidt (1989) is applied to treat the problem of rough surface scattering. A linear system is then established to facilitate the computation of the coherent reflection field. The coherent reflection coefficients for various surface roughness, sediment randomness, frequency, sediment thickness, and basement elasticity have been generated numerically and analyzed. It was found that the higher/larger size of surface and/or medium randomness, frequency, thickness, and shear-wave speed, the lower the coherent reflection. Physical interpretations of the various results are provided.

Acoustic plane-wave reflection from a rough surface over a random fluid half-space

Plane-wave reflection from a rough surface overlying a fluid half-space, with a sound speed distribution subject to a small and random perturbation, is considered. A theory based upon a boundary perturbation method in conjunction with a formulation derived from Green's function for the coherent field in the random medium have been applied to a typical oceanic environment to study their effects on the plane-wave reflection. By considering the coherent field itself, the plane-wave reflection may be obtained straightforwardly through a procedure consistent with the formalisms currently employed in rough surface scattering. The results show that both the rough surface and medium inhomogenieties may reduce the plane-wave reflection, however, the characteristics of the curves representing their effects are different, enabling us to identify the dominant scattering mechanism. The results for the coherent reflection due to the individual scattering mechanism are compatible with those found in the existing literature.

Coherent Reflection of Acoustic Plane Wave from Rough Interfaces in a Stratified Random Fluid Medium

Coherent reflection of an acoustic plane wave from rough interfaces in a horizontally-stratified medium, within which the sound-speed distribution subject to a small and random perturbation, is considered in this paper. The general formulation based upon the theory for rough-interface scattering in a stratified medium, in conjunction with that for random medium is derived. The Green’s function for a random medium bounded by two surfaces, which serves as generic solution of the problem, is obtained. The formulation is then applied to a simplified seabed environment to study the effects of surface roughness and medium inhomogenieties on the coherent reflection. The numerical results demonstrate that both the rough-surface scattering and medium scattering distract the energy from the coherent field, making the coefficient of the coherent reflection reduced with an amount, depending upon the degree of roughness and randomness measured by the relevant parameters. Furthermore, the characteristics of the distribution for the reflection coefficient with respect to incident angle show distinct feature, potentially allowing identification of dominant scattering mechanism.

Diffusive energy scattering from weakly random surfaces

We derive transport theoretic boundary conditions for acoustic wave reflection at a weakly rough boundary in an inhomogeneous half space. We use the Wigner distribution to go from waves to energy transport in the high frequency limit. We generalize known results on the reflection of acoustic plane waves in a homogeneous medium. We analyze higher order corrections, which include a enhanced backscattering effect in the back direction.

Effect of randomly inhomogeneous seafloor on the reflection and scattering of plane acoustic waves in shallow waters.

The bottom of the ocean is composed of randomly inhomogeneous, anisotropic layers of sediments. A geoacoustic data set is constructed from previously measured geological experiments in shallow-water regions of the New Jersey Continental Shelf. This data set is used as input for a stochastic reflection model based on the Monte Carlo technique in order to study the effect of the random variations of the seafloor properties on the scattering and reflection of acoustic plane waves in a shallow ocean. It is found that the random inhomogeneities as well as the anisotropy of the subsurface are major causes of volume scattering and certain anomalies in the reflection coefficient.