Wreck searching
In order to find wrecks on the sea floor we use traditional 2D sonar, side scan sonar and also down scan sonar.
When using the side scan sonar the sonar beam is like a flashlight hitting structures and casting shadows from objects on the sea floor.
Long shadows mean taller structures. Solid objects will give a clear strong return of the frequency beam sent out from the side scan sonar. Objects with less density will give a weaker sonar beam return. This means solid objects show up brighter than softer objects.