Sound diffraction by an underwater ridge with soft finite impedance

Laboratory experiments have been conducted in a water tank to investigate s ound propagation over an underwater ridge with soft, finite impedance, very low density (0.12 kg/m(3)) and sound speed (250 m/s), and very high attenu ation (2-3 dB/cm in the frequency range of interest of 50-85 kHz). The diff racted acoustic pressure was measured along the ridge surface and along a v ertical axis behind the ridge. Good agreement was found between predictions from the theory of matched asymptotic expansions (MAE) and the experimenta l data. The diffracted sound field is quite sensitive to the acoustic atten uation of diffraction material, thus showing potential as an inversion tech nique to characterize soft material attenuation. (C) 2001 Acoustical Societ y of America.