2025_programme: Quantitative Measurements of the Characteristics of Shoaling Internal Wave Boluses Using Synthetic Aperture Sonar

• Day: June 19, Thursday
    Location / Time: A. TERPSIHORI at 14:50-15:10
• Last minutes changes: -
• Session: 12. Observing the Oceans Acoustically
  Organiser(s): Bruce Howe, Kay Gemba
  Chairperson(s): Bruce Howe, Kay Gemba
• Lecture: Quantitative Measurements of the Characteristics of Shoaling Internal Wave Boluses Using Synthetic Aperture Sonar [Invited]
  Paper ID: 2225
  Author(s): Anthony Lyons, Roy Hansen
  Presenter: Anthony Lyons
  Abstract: Quantifying the physical characteristics of shoaling internal waves would allow better estimates of the important oceanographic properties of heat transport, turbulent mixing, and energy dissipation. Owing to acoustic focusing effects, Synthetic Aperture Sonar (SAS) has been shown to have a surprisingly good ability to detect internal waves and boluses formed after wave breaking events. Internal waves and related features such as boluses change the water column sound speed structure and therefore affect images of the seafloor by focusing or defocusing transmitted acoustic energy. Although not collected expressly for the purpose of internal wave research, existing complex SAS image data collected during previous sea trials by the Norwegian Defence Research Establishment (FFI) has been used to develop a multi-look technique to quantify spatial and temporal characteristics of shoaling internal wave boluses. In the multi-look technique, a single-look complex image is used to form several sub-band images by dividing the 2-D wavenumber spectrum into along-track sub-bands then reforming lower-resolution images with different viewing angles onto the imaged scene. The apparent shifts (or disparity) in features that exist between images with different look angles, such as the focus/shadow regions in the sub-band images, can be used to estimate characteristics of the internal wave or bolus, such as height. Example results of this methodology, implemented using SAS images, will be given during this talk, and compared to previously reported measurements.
• Corresponding author: Dr Anthony Lyons
  Affiliation: University of New Hampshire
  Country: United States