AUH (Autonomous Underwater Hydrophone)

· Can be deployed off a ship at any spot in the ocean where we want to listen

· The instrument is anchored to the seafloor, and a floatation device suspends the hydrophone in the ocean.

· By studying the frequency characteristics of the sound signals recorded by the hydrophones, we can glean a large amount of geological and biological information.

· With the hydrophone, can record the very low-frequency, infrasonic signals of earthquakes, volcanic eruption and blue and fin whale calls.

· Can record the audible sounds of passing ships, the background rumble of passing storm systems. 

·         a microphone designed to be used underwater for recording or listening to underwater sound. 

·         Most hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure change.

·         Can convert a sound signal into an electrical signal since sound is a pressure wave. 

·         Some transducers can also serve as a projector, but not all have this capability, and some may be destroyed if used in such a manner.
·         A hydrophone can "listen" to sound in air but will be less sensitive due to its design as having a good acoustic impedance match to water, which is a denser fluid than air. Likewise, a microphone can be buried in the ground, or immersed in water if it is put in a waterproof container, but will give similarly poor performance due to the similarly bad acoustic impedance match.