Side-Scan Sonar

Examples of CSA International's Marine Field Operations Services:

• Integrated Video Mapping System
• Side-Scan Sonar
• Subbottom Profiling
• Underwater Technical Services
• Vibracoring
• Coastal Survey Vessel
• 25ft Work Barge
• Environmental & Biological Surveys
• Offshore & Underwater Photography

Side-Scan Sonar

OVERVIEW
Side-scan sonar is a widely accepted tool for mapping the surface topography of the seafloor. The capability to cover hundreds of meters on each side of a moving survey vessel provides an excellent means to rapidly survey areas of interest. The side-scan sonar towfish contains transducers that project high intensity, high frequency bursts of acoustic energy in thin fan-shaped beams that are narrow in the horizontal plane and wide in the vertical plane. These acoustic signals are projected over the seafloor on both sides of the towfish. Echoes that bounce back from targets on the seafloor are received by the transducers, amplified, and transmitted up the tow cable to the graphic recorder on the survey vessel. The recorder processes the acoustic data that are printed on paper scrolls, creating a permanent, continuous graphic record of the seafloor surface topography. The raw sonar data also are tape-recorded for future playback and processing.

APPROACH
Continental Shelf Associates, Inc. (CSA) has employed side-scan sonar tools in various configurations since 1978 to address many different project goals. Most of CSA's current side-scan sonar work is conducted using a Klein Model 595 dual frequency (100/500 kHz) system. With tow cable and winch configurations appropriate to the project water depth and conditions, CSA typically uses the system in conjunction with CSA's Navigation and Data Acquisition System (NADAS). CSA's NADAS is a modular computer software and hardware package that interfaces the side-scan sonar and various other data collection sensors with the positioning system in use. The NADAS enables the survey team to pre-plot survey lines or positions and also use the system for vessel guidance, data logging, and real-time vessel track plotting. The NADAS feeds fix marks, towfish positioning coordinates, and water depth data to the side-scan sonar system's graphic recorder, which in turn prints these data along the edges of the side-scan sonar scrolls. With slant range and vessel speed correction capabilities, the resultant records provide excellent raw data for digitizing polygons and targets to depict selected interpreted seafloor features. These digitized seafloor features then are imported into the desired reporting software package, such as a Computer Aided Drafting (CAD) or Geographic Information System (GIS) program.

APPLICATIONS
Side-scan sonar systems have seen widespread commercial and military applications in many phases of underwater mapping, search, and recovery. They have been used extensively in oceans, inland lakes, rivers, harbors, and canals. Some typical applications include the following:

• Environmental Habitat Characterization - One of the most important applications for the system is to provide a complete seafloor features map with overlapping coverage showing the different seafloor topographies that would support various ecological communities. By displaying a "top" view, quantitative areal assessments can be made.
• Fisheries Applications - The system can be used for a variety of fisheries research tasks, including density measurement of biological targets such as schools of fish and mapping of habitat size and location.
• Geological Studies - The sonar is able to recognize both small and large features of the ocean bottom such as rock outcroppings, reef, rough and smooth mud, sand, gravel, and other bottom types.

Pre- and Post-Cable and Pipeline Surveys to detect environmental conditions or bottom hazards along a route. Engineering Surveys on bottom conditions prior to structure installation. Military Applications for route surveys, location of downed aircraft, and other specialized applications. Wreck Location and General Searching for objects including well heads, downed aircraft, debris fields, and shipwrecks.