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Groundfish Assessment Program

Habitat Research Group Takes Delivery of Two Long-Range Sidescan Sonar Systems

inspection of sidescan sonar
John Roscigno, L-3 Ocean Systems Director of Advanced Programs, and FISHPAC chief scientist Bob McConnaughey during the final inspection of two long-range sidescan sonar systems at the L-3 facility in Sylmar, California.  Photo by Mike Webb.

The broad scope of the Congressional essential fish habitat (EFH) mandate requires an efficient process for describing and mapping the habitat needs of all Federally managed species. In 2004, the Government awarded a $3.6 million contract to L-3 Klein Associates, Salem, New Hampshire, for two long-range sidescan sonar systems (LRSSS) for fisheries research.

These prototypes are capable of very broad coverage at high speeds, as compared to conventional towed systems. This capability increases the area of seabed that can be mapped per survey day, thereby improving vessel productivity.

The LRSSS is a towed underwater platform (towfish) with multiple acoustic, environmental, and navigational sensors which, combined with topside processing electronics, efficiently collects, processes, and archives quantitative data to characterize the seabed for EFH research.

The subsurface unit (SSU) generates coregistered, high-resolution, dynamically focused multibeam sidescan imagery, multibeam echosounder bathymetry, and 38 kHz single-beam echosounder data. Auxiliary sensors provide full attitude instrumentation and continuously monitor towfish altitude, depth, and speed over ground; water temperature; sound speed; and the concentrations of dissolved organics, chlorophyll-a, and total particulates in the tow path.

The SSU is also configurable for hull-mounted operations, such as may be required for use in shallow water. The topside subsystems coordinate manipulation, storage, and display of raw and processed data, while also supporting operator control of towfish pitch, roll, and angle of attack when under way. Specialized software developed for the project geocodes and merges the backscatter and bathymetry data, normalizes backscatter data across the swath by correcting for radiometric and geometric effects, then generates 20 different summary statistics and full-swath mosaics of the data for operator-specified grids of the seafloor.

Delivery of the two systems was originally scheduled for February 2006, but was delayed until December 2009 because of technical difficulties affecting key performance requirements. Several major design changes occurred, and over 250 individual tests and inspection procedures were performed in the factory and at sea to characterize the LRSSS prior to delivery.

The NOAA project team, consisting of Lloyd Huff (University of New Hampshire Center for Coastal and Ocean Mapping), Bob McConnaughey (AFSC) and Mike Webb (NOAA Marine Operations Center Pacific), worked closely with the manufacturer and the NOAA contracting officer to complete the procurement.

Immediate plans include formal training in LRSSS operation and post-acquisition processing methods to be provided by the manufacturer. Sea trials will be conducted in local waters, and miscellaneous system improvements will be completed during 2010 in preparation for an integrated ocean mapping cruise in the eastern Bering Sea (EBS).

This FISHPAC-project cruise will 1) investigate the utility of acoustic backscatter for characterizing the EFH using a variety of sonar systems (including the LRSSS), 2) determine the most cost-effective sonar methodology for large-scale mapping of EFH in the EBS, 3) evaluate the mechanism of association between groundfish and surficial sediments, and 4) provide hydrographic-quality bathymetry data to the NOAA Pacific Hydrographic Branch for updating nautical charts in areas with outdated or nonexistent information.

By Bob McConnaughey

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