Abstract:

A laboratory experiment was conducted to investigate the effects of small-scale random roughness on acoustic propagation across a fluid--fluid interface. This experiment utilized an acoustic source mounted onto a movable platform, several hydrophones, and two immiscible fluids (vegetable oil and glycerin). The effects of roughness on propagation across the interface were determined by floating small polystyrene beads at the interface between these fluids. Data were collected as functions of frequency, grazing angle, and varying degrees of roughness (bead size and with/without beads). The goal of this experiment was twofold: (1) to test roughness diffraction as a mechanism for enhanced acoustic transmission at grazing angles shallower than critical, and (2) to assess the temporal and spatial coherence of the transmitted signal. Analyzed data of this work will be presented and compared to results of propagation into underwater sediments reported in the literature. [Work supported by ONR.]