How is the depth of sea measured using ultrasonic waves?

Answer 1

It's done using exactly the same principle as radar:

-- You know the speed of sound through the seawater.

-- You send out a pulse of sound underwater ... a tremendously loud "BEEP". Also, at exactly the same instant, you start a clock.

-- The sound travels down to the bottom and hits the sea floor. Some of the sound is absorbed, and some bounces off of the sea floor. The part that bounces off sprays away in all different directions. A small part of the sound energy goes back exactly the way it came ... back toward your equipment on the boat.

-- Back on the boat, your clock is still running, and your sensitive equipment is listening for a weak echo of a beepto come up from the sea floor. When it hears the echo, the clock stops.

-- Multiply the (speed of sound in the water) by the (length of time it took for the beep echo to return). The answer is the (distance the sound traveled on its round-trip) ... which is exactly double the depth of the water under the boat.

Ultrasonic (inaudible) sound is used for two main reasons:

1). Shorter wavelengths can resolve smaller details, giving a clearer picture of the topography on the sea floor. Same reason 'ultrasound' is used for medical imaging.

2). Probing with loud audible sound signals would drive the people on the boat crazy. So they use sound that people can't hear. That way, only all the whales and other sea life within a thousand miles are upset and irritated and have their feeding and mating processes and social communication disrupted.