End-fire Synthetic Aperture Sonar for Seafloor Volume Scattering Studies

TitleEnd-fire Synthetic Aperture Sonar for Seafloor Volume Scattering Studies
Publication TypeJournal Abstract
AuthorsSteele, SM, Lyons, AP
JournalThe Journal of the Acoustical Society of America
Date SubmittedNovember 2017
KeywordsSeafloor Characterization, seafloor scattering, synthetic aperture sonar

Acoustic returns from seafloor sediment are comprised of scattering from both the interface and sediment volume. Although volume scattering is often the dominant mechanism, direct measurements of this component have rarely been made, if at all, due to interface roughness biasing. This bias is especially prevalent at lower frequencies where beam widths are typically 30-40 degrees. Current synthetic aperture sonar (SAS) systems are side looking and achieve narrow beam widths by coherently combining multiple acoustic pings as the sonar moves. End-fire (forward-looking) SAS would formulate a synthetic array in the same direction of travel by vertically orienting a transducer and lowering it towards the seafloor while pinging. This would create a narrow beam, significantly reducing the interface roughness bias. End-fire SAS array gains are not as substantial as conventional side-looking SAS. However, beam pattern simulations suggest the gains are still significant: a synthetic array length of 100 wavelengths can reduce a sub-bottom profiler’s 40 degree beam width to 7 degrees. This talk will discuss proof of concept, motion controlled experiments performed in an acoustic testing tank and in the field.