Seeing With Sound

Side Scan Sonar (SOund NAvigation and Ranging) was developed in the 1960s and is a sonar signal that can look sideways. It can be compared with radar, but uses sound echoes and measures their changes as they reflect off of the seabed.

The sound pulses are commonly transmitted from a towfish that looks much like a torpedo. The pulses are sent in a wide pattern down to the bottom and the echoes are received back in fractions of a second. As a result, each pulse shows a narrow strip below the towfish and to the sides. As the towfish is dragged behind the boat, an image is displayed on a laptop computer.

The resulting image provides useful information about the topographic relief of the sea floor (or in our case the bottom of the St. Lawrence Seaway channel) and provides images that can be quite revealing. Below is an image that provides an example of a sunken ship as revealed by side scan sonar.

Image Courtesy of JW Fishers