Scanning Sonar for Search and Survey

By Marine Technology Reporter

When an SUV went off a Minnesota bridge and into a river in January the local sheriff’s office was immediately notified and the Winona County Dive Team dispatched. Two bodies were quickly recovered from the vehicle, both wearing seatbelts, but two others were missing. The third victim was found the next day, but the fourth could not be located. Frigid water and limited visibility made a large scale search operation with divers nearly impossible. A decision was made to call in nearby Washington County Sheriff’s Department and its underwater robot. Two years earlier the department had acquired JW Fishers SeaOtter-2 ROV which has two cameras, four thrusters and a SCAN-650 scanning sonar. The SCAN-650 allows the operator to see much further than the video camera because the sonar’s sound wave sweeps a 200 ft. diameter circle around the ROV. The wave bounces off any object on the bottom and is sent topside where it produces an image of the object on a laptop computer. Using their ROV equipped with scanning sonar the Washington team was finally able to locate the fourth victim 125 ft. from where the vehicle entered the water and on the opposite side of the bridge.

(As published in the March 2014 edition of Marine Technology Reporter -

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