I am a scuba diver, with a big idea that would require me to map various dive sites as I went to them and dove in them. The typical size and other implications of sonar technology would essentially render this impossible.
So I thought, would it be possible to use ultrasound instead? This would theoretically require a device that could, instead of seeing through the warm gel that hospitals use, see through cold ocean water. I've done some research but have not gotten a definitive answer, which is understandable since no one has asked the question.
And, secondly, if ultrasound is not possible, what else is typically (or not typically) used in oceanography besides sonar?