Texas A&M University
Department of Oceanography

Winter 1998 / Spring 1999 - Vol. 6, No. 3

Measuring the Depths

Side-scan sonar

 Another way of explaining side-scan sonar:

Imagine that you are looking for something -- such as your lost keys -- in a dark room.

More ...

 Like the multibeam echo sounder, a side-scan sonar sends out a fan-shaped pulse of sound, but it works on a slightly different principle. Whereas the purpose of the multibeam echo sounder is to measure ocean depth, the side-scan is designed to make an image of the seafloor.

Making a mosaic [25 K]

A side-scan sonar "fish" is connected to a long cable and towed behind a ship. In order to figure out where the sound came from, it measures the time it takes for the sound to hit the seafloor and come back. The sonar typically plots a strip of seafloor with a width several times the distance from the sonar to the bottom. For example, a long-range side-scan might make a swath 2-3 kilometers wide in 500 meters of water depth. After running a line several tens of kilometers in length, the ship moves over to a parallel track to run an adjacent swath.

Sidescan geometry [19 K]

A side-scan sonar converts the intensity of returned sound to grayscale (black and white and shades of gray) and forms an image of the seafloor. In 500 meters of water depth, the sonar will plot a strip of the seafloor about three kilometers wide and 20 kilometers long. Then the ship will turn around, move over 1500 meters and tow over another strip of the seafloor alongside the first strip.

Towfish track
[15 K]

Click on the illustrations on this page for more information!

http://oceanography.tamu.edu/Quarterdeck/1998/3/sager-5.html
Copyright 1998-1999, Department of Oceanography, Texas A&M University.
Updated November 24, 1998. (abdw)

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