A western perspective on research in underwater acoustics and acoustical oceanography

Abstract

Underwater acoustics and acoustical oceanography are both concerned with sound underwater, the distinction between them being that the former deals primarily with forward problems such as acoustic propagation and scattering, whereas the latter involves the inversion of sound fields to obtain information about the oceanographic environment. Over recent years in the USA and Europe, both disciplines have tended to move away from the use of dedicated acoustic sources, over concern about damage that such sources may inflict on marine mammals. Ambient noise has, to some extent, replaced dedicated sources as the sound field of choice, since it offers the prospect of returning a wealth of information about ocean processes but without the threat to the marine mammal population. To extract such information, the properties of the noise field itself must be well understood (underwater acoustics), as must the inversion procedures necessary to recover the information contained in the noise (acoustical oceanography). A brief introduction to the properties of ambient noise fields will be followed by several examples of noise inversions, the latter illustrating not only the utility of ambient noise inversions but also the complexity of typical noise fields in the ocean. (Research supported by the Office of Naval Research).