New findings on scattering from floating plate with lateral heterogeneities

Abstract

Experimental ultrasonic modeling results are presented on near grazing incidence scattering from cracks, ridges, and edges of floating plates bounding a shallow water waveguide. It was observed that underwater acoustic waves propagating in a shallow water waveguide bounded by a floating plate produce a ringing wave component in the water upon scattering from a crack or a plate edge. This ringing component is associated with the water wave, travels with the water wave velocity, and its time of arrival is independent of the length of plate region along the wave path. The ringing frequency, however, is determined by the shear wave velocity and the plate thickness. The plate thickness corresponded to half a wavelength based on the shear wave velocity. The contribution of the ringing wave component to scattering from wet cracks, dry cracks, and ridges are demonstrated. The impact of these new findings on interpreting laboratory scaled studies on Arctic acoustics are discussed in view of the wide use of Plexiglas to model sea ice. Examples are given on scattering from single and multiple cracks and ridges. [Work supported by DREP and ONR.]