Let's say you have a sound source, in the ocean, at a frequency around 50 kHz. It's a point source, so the sound waves emanate in all directions. Some will go straight up. Do these straight up sound waves reflect off the surface and go straight down?
If no, then where does the sound energy go? Into the air? How could the much less dense air absorb the sound so quickly?
If yes, why? What is it about the surface that reflects sound? I know a steel hull of a ship reflects sound waves, and steel is much more dense than water, so why would a much less dense entity (air) reflect anything?
I guess another way to ask this is, what is the critical angle in this situation? I've only ever heard that term in reference to light waves, though. I don't know if underwater sound waves also have total internal reflection in some circumstances, or what the critical angle would be.