St. Petersburg Coastal and Marine Science Center
The sidescan sonar (SOund NAvigation and Ranging) system is designed to image the seafloor by transmitting sound energy and analyzing the return signal or echo that bounces back from the seafloor or from submerged objects. A towfish transmits energy in a fan shape to both sides of the track line. The fan width varies with the frequency of the sonar system. Seabed features are characterized by mapping the intensity of reflected returns from different materials. The shape and character of features on the bottom are displayed in gray-scale images. More advanced sidescan units include a vertical 'pinger' that provides a simultaneous estimation of depth directly below the unit.
The USGS acquisition systems include ISIS systems, MarineSonic SeaSoft systems and SeaSwath systems.USGS instruments: EdgeTech 272TD towfish, MarineSonics 1200 KHz towfish, and SEA SWATH+H 468 KHz Swath Bathy sidescan.
For more information: USGS Professional Paper 1634, J.G. Flocks, Chapter B, New Field Sampling Techniques and Data Description in Lake Pontchartrain Basin: Bottom Sediments and Related Environmental Resources