Application Tips and Tricks

Scan From Above

This is to illustrate the benefit of scanning from above a target. The basic idea is to get up above the bottom and angle the sonar downward slightly. The benefit is that objects projecting above the bottom cast an "acoustic shadow" behind them which tends to highlight them on the sonar image and gives an indication of their height.

This is true for any imaging sonar including side-scan sonars, multibeam sonars, and indeed also for the Omniscan 450 FS sonar.

Here is an image from SonarView showing a sunken boat. You can clearly see the shadow behind the barge. The sonar was about 15 meters above the bottom when this data was taken.

You mustn't take the beam specs too categorically. Generally the beam widths are given at the -3dB point, but there is plenty of acoustic energy beyond there. It is good to have some energy going straight down to get a sense of the depth. But you don't need a lot of energy in that direction because the bottom as a broadside target is a pretty good reflector. It's really a function of desired range and height above the bottom.

About "beam widths" and transducer mounting angle. Don't take the beam specs too literally, particularly in the wide dimension of the fan beam. Generally the beam widths are given at the -3dB point, but there is plenty of acoustic energy beyond there. It is good to have some energy going straight down to get a sense of the depth. But you don't need a lot of energy in that direction because the bottom as a broadside target is a pretty good reflector.

So It's really a function of desired range and expected height above the bottom. 20-25 degree downward tilt is probably optimal for longest range relative to height, but if looking at nearer targets from higher altitudes, a larger angle may be more appropriate.