Sonar uses sound to locate objects underwater. It works in a similar way to echolocation in animals such as bats or dolphins. A sound is produced, either artificially or from a natural cause, and then the sonar system measures the timing (and potentially distortions) of echoes from objects. Objects that are further away from the source and recever take longer times and the material or speed of the objects may chnage the characteristics of the reflected sound. In more complex systems multiple object-object reflections may give additional information. Sonar or similar systems using electomagnetic waves may be used in robots to help in navigation or obstacle avoidance, or in permanant installations to to detect the movement of people or objects within a space.
Used on Chap. 15: page 351