SUPPORT > SIDE SCAN IMAGERY > ACOUSTIC SHADOWS

When sound from the sonar hits a submerged target with any height above the seabed, an acoustic shadow will be cast away from the sonar.

An experienced sonar operator can use the lengths of these shadows, along with knowledge of the sonar altitude to get an idea of the size and height of the object.

To help understand this, imagine you are in a darkened room, with a flashlight, standing above a ball. If you shine the flashlight down on the ball, a small shadow is cast around it, while if you lie down level with the ball and shine the light at it, a much longer shadow is produced stretching away from it.

This principle applies to side scan sonar in a similar way; objects directly beneath the sonar will appear to have very small shadows, while objects at greater distances will have longer shadows because they are being illuminated (acoustically) on their side.

The shadows of targets can be elongated further if the towing altitude of the sonar is decreased or if in shallow water.