Scattering from Submerged Objects and the Seafloor

A study of acoustic localization, imaging and classification of submerged objects is important in such iverse areas as antisubmarine warfare, marine-mammal abundance and behavior studies, and both ROV and AUV operations. This is primarily because sound is the only means available for long-range sensing in the ocean. A full 3D spectral approach to scattering from objects submerged in a layered medium, such as the ocean, has recently been developed. This theory has been applied to the scattering from common objects, such as spheres and plates, submerged in a shallow-water wave guide. In doing so, Professor Makris has discovered that there are significant differences between scattering in free space and in shallow water. In addition, he has shown that the standard sonar-equation approximation for estimating the scattered field from a submerged object can be in error by orders of magnitude for many common situations. The scattering from submerged objects also has an interesting application in the study of the song of the humpback whales of Eastern Australia. In fact, Professor Makris and his Australian colleague, Dr. Douglas Cato, have hypothesized that the whales may be able to use the vocalizations of a member of the herd to echo-locate nonvocal members comprising the majority by a factor of 10. They have made some preliminary calculations based on sonar information theory that show that their hypothesis is plausible.