Abstract:
High-frequency sound diffraction over an undulating sea bottom, including underwater ridges and hills, has become of increasing interest to the ocean acoustic community. In many cases, the top layers of the seabed are relatively soft. Thus, sound diffraction by an underwater ridge with a very soft boundary (closed-cell foam material) is investigated in a laboratory tank. The diffracted acoustic pressure is measured in the penumbra, along the ridge and along vertical axes behind the ridge. Experimental data are compared with Fock and Pierce's theory, which originally described the diffraction field of an electromagnetic wave propagating over a curved conducting surface. Experimental data and numerical results are in good agreement. The insertion loss caused by the underwater soft ridge is much higher than that caused by a rigid ridge. [Work supported by ONR.]