It is very difficult to hear underwater sounds from above the surface of a body of water. This is suggested to be due to the speed of sound being very different in air versus water, leading to most underwater sound being reflected back into the water, and not passing into the air.
Am I supposed to think of the air-water interface as some sort of plane mirror then? I have heard of Snells law for refraction, but am not sure how it applies to reflection in this case. If I am to think of the interface as a mirror, I might expect a very thin layer of water to have equal reflection/reflectivity compared to a thick one. Is this the case?
If not, how can I better think about what is going on? Also, is there interplay between the wavelength of the sound and the thickness of the water layer required for reflection?
Best Answer
Within reason, a thick sheet of water and a thin one will affect sound mostly the same.
With extremely large thicknesses, sound actually transmits better.
When the thickness approaches a wavelength of the sound in question, the equations get a bit more complicated. I'd be wary of venturing a guess in this regime.