What is happening in the diagram ;

*my attempt to describe.*
There is a modern sail boat on the surface of the water, point A is a set of waves (they look like the curved lines on per say your volume icon; ))) ) that go down to a boat wreck(point B) on the ocean's floor. Point C is another set of the waves going up to hit the bottom of the sail boat.
I believe it is some sort of set of vibrations being sent through the water but I do not know if there is sonar involved.
Help is greatly appreciated.

2 answers

it appears that the sailboat is using sonar to locate the wreck
By the way those are not electromagnetic but acoustical.