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Finite Element Modeling of Acoustic Scattering From Fluid and Elastic Rough Interfaces

Quantifying acoustic scattering from rough interfaces is critical for reverberation modeling, acoustic sediment characterization, and propagation modeling. In this study, a finite element (FE) scattering model is developed. The model computes the plane wave scattering strength for an ensemble of rough power-law surfaces for ocean bottoms described as fluid and elastic. The FE model is compared with two models based on approximations to the Helmholtz-Kirchhoff integral: the Kirchhoff approximation (KA) and the perturbation theory (PT). In the case of a fluid-like bottom, the KA and FE models agree except at small grazing angles. The PT and FE models deviate near specular especially at small angles. For the elastic case, the PT predicts the FE results well except at the intromission angle of the shear wave. The KA deviates for angles that are below the critical angle of the compressional wave. At the shear wave intromission angle, the FE model shows a more plausible solution likely due to multiple scattering events that are not accounted for in PT for the modeled roughness.