It's a little pathway in the ocean where sound can travel a very long way in a very quiet, fairly isolated layer. Submarines avoid it. Submarine detection in the sound channel is a big suspenseful part of it. Great film, too.
Sound travels faster in warmer water, slower in cooler water.
By measuring the time between when a sound is made and when it's heard, scientists can determine the average water temperature along the sound's path. Well, I think it's fascinating. Man, I can't believe I'm almost done with the semester. I don't want Oceanography to be over. I am, on the other hand, totally ready for Biology to be over.