Abstract:
Interface waves often play a significant role in seafloor propagation and scattering problems. Because they are not solutions to the pure acoustic wave equations, but require a nonzero shear modulus, they are frequently overlooked in model and inversion studies. There are two areas in particular where interface waves are relevant in underwater acoustics: (1) when the source and receiver are close (in terms of wavelengths) to the seafloor, and (2) when interface roughness or heterogeneities near the interface act as secondary scatterers. The first case is important for low-frequency propagation in shallow water. The second case is important in scattering problems such as low-angle, monostatic backscatter or the scattered field of seafloor or buried ordinance. Insight into the generation and propagation mechanisms of interface waves can be gained through time-domain shapshots of the wavefield and by analysis of time series record sections. Animations of wavefront propagation in vertical slices through the seafloor show clearly the energy partitioning between the various body and interface wave types. [Work supported by ONR.]