Underwater sound scattering by marine organisms. A review

Scattering of acoustic energy by inhomogeneities within the water column, or volume reverberation, is a major source of interference to underwater sonar systems. As naval defence systems have a high dependence on acoustic detection, knowledge of the factors that affect sonar interference is relevant to defence interests. The literature on interference to sonar propagation by marine organisms is reviewed, with particular emphasis on Australian waters. Acoustic scattering in the ocean generally occurs in discrete layers called deep scattering layers. Theoretical and experimental investigations show conclusively that the scattering is caused by marine organisms. Reverberation profiles are dominated by the resonance back-scattering from gas-filled swimbladders of midwater fish, particularly at frequencies between 0.5 and 20 kHz. At higher frequencies, scattering from fish tissue and planktonic organisms becomes significant. Information on the identity and acoustic properties of sound scattering organisms within the Australian region is sparse.