Hydrophone is an underwater device that detects and records ocean sounds from all directions.

It just as a microphone collects sound in the air, hydrophone detects acoustic signals under the water. Most hydrophones are based on a special property of certain ceramics that produces a small electrical current when subjected to changes in underwater pressure. When submerged in the ocean, a ceramic hydrophone produces small-voltage signals over a wide range of frequencies as it is exposed to underwater sounds emanating from any direction.

Hydrophones measure ocean sounds with great precision by amplifying and recording these electrical signals. While a single hydrophone can record sounds from any direction, several hydrophones simultaneously positioned in an array, often thousands of miles apart, result in signals that can be manipulated to “listen” with greater sensitivity than a single device. Omni-directional and hemi-directional hydrophones pick up sound from a particular direction and can be used to track fish movements.

A hydrophone with a single transducer has a circular conical shape that reflects incoming sound waves which in turn allows the hydrophone to be positioned at varying locations and depth.

Array hydrophones (streamers - built of multiple transducers) are all wired to collectively receive a large sound signal. The transducers are packed together in a tube with oil which aids the collection of pressure waves entering the hydrophone.