Development and Experimental Validation of End-Fire Synthetic Aperture Sonar for Sediment Scattering Studies

TitleDevelopment and Experimental Validation of End-Fire Synthetic Aperture Sonar for Sediment Scattering Studies
Publication TypeThesis
AuthorsSteele, SM
Degree and ProgramMaster of Science
Number of Pages100
Date PublishedMarch
UniversityUniversity of New Hampshire
LocationDurham, NH

Seafloor sediment acoustic returns are comprised of scattering from both the sediment-water interface and the sediment volume. At low-frequencies, volume scattering is often the dominant mechanism; however, direct measurements of this component have rarely been made, owing to the large beamwidths typically associated with low-frequencies. When beamwidths are large, the sediment interface and volume returns arrive at the same time, causing estimates of volume scattering to become biased by the interface scattering. End-Fire Synthetic Aperture Sonar (EF-SAS) can achieve narrower beamwidths by coherently combining multiple acoustic returns as a vertically oriented transmitter and/or receiver is moved towards the seafloor. A beampattern model developed for EF-SAS suggests EF-SAS processing can reduce the beamwidth of a sonar by a factor of five with an array length of 100 wavelengths. In this thesis, EF-SAS processing methods were developed and the resulting gains were experimentally verified through a motion-controlled EF-SAS field trial. Experimental tests indicate that EF-SAS gains can be accurately predicted using the EF-SAS beampattern model. Analysis of the data demonstrates the ability of EF-SAS to reduce interface scattering. EF-SAS can produce a variety of data products relevant to seafloor characterization, including: the angular response of interface and volume scattering, the sediment reflection coefficient, and the sediment attenuation coefficient. This thesis concludes with recommendations for the development of a specialized EF-SAS tool, and an analysis of its applications.