relevé hydroacoustique

CONT: An acoustic survey is a method of gathering information on the abundance of a fish species using echo sounders. Sound is a form of energy which travels farther and faster underwater than in the air. So using the distance a sound travels and the record it makes when it bounces off of something underwater can tell a researcher a good deal about the creatures passing by underwater.
OBS: In an acoustic survey, a transducer emits a pulse of sound. The transducer can be either fixed or mounted on a moving vessel. The sound moves through the water until it bumps into something, such as a fish, and part of its energy is reflected back to the transducer. Another device, called an echo sounder, amplifies the returned energy and sends it to a recorder where it registers as a mark.