This is a third kind of sonar it is similar in some ways to the scanning sonar, in that it used a single fan shaped beam (actually two one on each side.) But rather than a mechanical rotating head, a fixed head on a device called a “towfish†is pulled through the water on a cable (or attached to a ship hull.) See http://en.wikipedia.org/wiki/Side-scan_sonar .
This is a wide area search tool a boat towing a side scan can image a much larger area than a VideoRay could. If you are searching for something or creating a map, and the area involved is large, a side scan survey is often the first thing you want to do. After this survey has identified likely targets, a secondary detailed imaging with a VideoRay is often the next step. According to John De Mille of Marine Sonic Technology (www.marinesonic.com ), a leading Side Scan Sonar company, Side scan sonar and the VideoRay ROV are complementing tools. The side scan will give an image that may confirm, but many times further examination is required and that is a good task for a VideoRay ROV. The area that can be covered is about the area of a football field in about a minute when employing side scan sonar. Procedure is: search, locate with side scan sonar, investigate and recover with VideoRay ROV.