The side-scan sonar resembles a torpedo and is designed to be towed behind a boat. A transducer, which is housed in a tow fish in the device, transmits “pings” of sound through the water a few feet above the bottom. The reflected acoustic returns are processed into an image similar to an aerial photography, which is viewed real-time on a computer monitor aboard the boat. Typically, the side-scan sonar searches a swath of 60-160 feet wide at about 2 miles per hour, although other ranges can be used depending upon the size of the object being sought.
Location information from a differentially corrected global positioning system (DGPS) is used to guide the towing vessel along predetermined search lines as well as to identify the location of any point on the side scan image. The stored GPS location information allows the searchers to return to any point in the image for further investigation or recovery.
This technology is capable of effectively searching large areas quickly, with little information for a starting point. It excels in instances where traditional techniques like divers, underwater cameras and drags are used; saving time, minimizing the danger to searchers and eliminating the element of chance from the recovery operation.