Remote sensing of submerged objects and geomorphology in continental shelf waters with acoustic waveguide scattering

The long range imaging of submerged objects, seafloor and sub-seafloor geomorphology in continental shelf waters using an active sonar system is explored experimentally and theoretically. A unified model for 3-D object scattering and reverberation that takes into account the coupling between propagation and scattering in a stratified medium is developed from wave theory. The conditions necessary for scattering in a waveguide to become diffuse is derived directly from Green's Theorem. Simulations with the unified model indicate that the detection of submerged target echoes above diffuse seafloor reverberation is highly dependent upon waveguide properties, bandwidth, array aperture, measurement geometry, and the scattering properties of the target. Analysis with the unified model shows that it is theoretically plausible for coherent returns from the scattering of evanescent waves by extended but discrete sub-bottom geologic features to stand significantly above diffuse or incoherent returns arising from small-scale roughness of the waveguide boundaries. A long-range bistatic sonar system was deployed in a field experiment and used to image extensive networks of buried river channels and inclined sub-seafloor strata over tens of kilometers in nearreal time. Such a capability is of great advantage in geophysical applications. Since buried river channels are expected to be ubiquitous in continental shelf environments, sub-seafloor geomorphology will play a major role in producing "false alarms" or cluster in long-range sonar systems that search for submerged objects such as underwater vehicles.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Ocean Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Ratilal, Purnima, 1971-

Advisor dc:contributor.advisor

• Nicholas C. Makris.

• Ocean Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/91377

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/91377