Scanning sonars assist underwater searches

5 February 2010

Scanning sonar is fast becoming one of the tools of choice for underwater search operations by a diverse group that includes public safety dive teams, universities, and commercial diving companies. Scanning sonars are in demand because they create a “picture” of the underwater environment regardless of water clarity. Although these sonars lack the long range and very high resolution of side scan, they can often still give a larger picture of the underwater environment than that of an underwater camera or diver. Even in areas where there is zero visibility, the sonar can produce a detailed image of objects on the bottom or in the water column.

Scanning sonar works by transmitting a sound wave from a transducer. This sonar beam sweeps an area underwater much like radar does in air. The beam reflects off underwater objects and returns to the transducer where it is received and sent to a topside computer for display and storage. Other information can be saved with the sonar data such as GPS coordinates and notes made by the operator.

The operator controls the size of the search area through the computer. The sonar beam can sweep a 360 degree circle around the transducer or any portion of the circle.

Another reason scanning sonar is so popular is its versatility. It can be operated as a “stand-alone” search system or mounted on an ROV. With the stand-alone version, the transducer is lowered from a boat on a pole, or mounted on a tripod and lowered to the bottom. After an area is searched, the sonar is retrieved and moved to a new area where the process is repeated.

With the ROV mounted version, as the underwater vehicle moves slowly along the sonar continually scans the course ahead. The sonar can “see” a much greater distance than the camera which lets the operator navigate around obstacles and helps in guiding the vehicle toward the target. Once it’s within visual range the ROV’s camera can take over and perform a close up inspection.

The University of Alaska is using a JW Fisher ROV with scanning sonar to help in its study of marine ecosystems. The school is part of a national cooperative program that promotes research in the management of fish and wildlife. It also has a Coastal Marine Institute. As part of an agreement between the university and the US Department of the Interior’s Minerals Management Service, the institute’s researchers explore coastal sites and assess the potential for development of natural gas, oil, and minerals.

Fishers scanning sonars are available in two types; the SCAN-650A designed for use as a stand-alone search system or for mounting on larger ROVs, and the SCAN-650B for use on smaller ROVs.

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