Swath mapping with a UniPulse hybrid sonar

Various autonomous survey strategies exist for autonomous seafloor swath mapping with semi-submersible platforms and with benthic platforms. The sonar system described here capitalizes on these survey strategies by improving two aspects: (1) the swath coverage, and (2) the realtime sounding uncertainty management to optimize the survey effort by minimizing data gaps and redundant coverage. Improvement in swath coverage is achieved by integrating two different swath mapping sonar architectures into a hybrid sonar transmitting a single acoustic pulse (UniPulse) per ping cycle. This hybrid sonar operates at 455 kHz and comprises a custom-built multibeam echo-sounder and an L-3 Klein S5000 V2 bathymetric sidescan sonar. The overall across-track swath coverage is about 160°. The multibeam echo-sounder receiver covers a 60^o sector centered at nadir, and the bathymetric sidescan sonar covers sectors extending on either side of nadir from 30° to 80°. This combination eliminates the central gap in coverage typical of bathymetric sidescan sonars, and provides a seamless acoustic backscatter image across track because the multibeam echo-sounder and the sidescan sonars receive the same transmitted pulse. A prototype of this hybrid sonar was tested at sea in April 2012, with the sonar mounted on the bow ram of a test vessel. These tests demonstrated the fully integrated bathymetry and acoustic backscatter imagery capabilities of the system at 10-25 m altitude.