sonar

A system using transmitted and reflected underwater sound waves to detect and locate submerged objects or measure the distance to the floor of a body of water.

An apparatus, as one in a submarine, using sonar.

Echolocation.

echolocation

A device that uses hydrophones (in the same manner as radar) to locate objects underwater.

a measuring instrument that sends out an acoustic pulse in water and measures distances in terms of the time for the echo of the pulse to return