Passive sonar systems are used primarily to detect noise from marine objects (such as submarines or ships) and marine animals like whales.

There are two types of sonar—active and passive.

By determining the time between the emission of the sound pulse and its reception, the sonar transducer can determine the range and orientation of the object.

Active sonar transducers emit an acoustic signal or pulse of sound into the water. If an object is in the path of the sound pulse, the sound bounces off the object and returns an “echo” to the sonar transducer.

Sonar uses sound waves to 'see' in the water.

Unlike active sonar, passive sonar does not emit its own signal, which is an advantage for military vessels that do not want to be found or for scientific missions that concentrate on quietly “listening” to the ocean.

Sonar is short for Sound Navigation and Ranging.