Side scan sonar also referred to as side-imaging sonar and side-looking sonar, is often towed from a survey vessel and has the ability to capture hundreds of meters of seafloor on each side of the moving vessel. The near photographic quality images produced by side scan sonar along with its ability to map large areas of seafloor quickly make it an essential piece of kit for anyone requiring high definition images of the seabed.

Side scan sonars transmit a narrow fan-shaped acoustic pulse (ping) perpendicular to its direction of travel. As the acoustic pulse travels outward from the side scan sonar, the seabed and other objects reflect some of the sound energy back in the direction of the sonar (known as backscatter). The travel time of the returned pulse is recorded together with its amplitude as a time series and sent to a topside console for interpretation and display. The topside console stitches together data from successive pulses, creating a long continuous image of the seafloor as the side scan sonar is towed from a survey vessel.

Interpretation of side scan sonar data develops with experience. Side scan sonar reflections of isolated small objects give no indication of shape or attitude. Manmade structures, such as platforms or rock walls tend to have regular patterns that are easier to identify. Increasing the scan range of the sonar severely limits the resolution in the far field of the acquired data and as a consequence interpretation becomes difficult.