Sonar

thumb|upright=1.35|French Georges Leygues-class frigate|F70 type frigates (here, ) are fitted with [[variable depth sonar (VDS) type DUBV43 or DUBV43C towed sonars.]] thumb|upright=1.35|A sonar image of the Soviet Navy minesweeper T-297, formerly the Latvian Virsaitis, which was shipwrecked in December 1941 in the [[Gulf of Finland.]]

A hydrophone () is a microphone designed for underwater use, for recording or listening to underwater sound. Most hydrophones contain a piezoelectric transducer that generates an electric potential when subjected to a pressure change, such as a sound wave.

method used by some animals to determine the location of something by measuring the time it takes for an echo to return from it

thumb|right|300px|Sonobuoy being loaded onto a USN P-3C Orion aircraft thumb|Hand deployment of a sonobuoy in the Arctic Ocean from the aft deck of the R/V Sikuliaq

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horizontal layer of water in the ocean at which depth the speed of sound is at its minimum

tool for seafloor mapping

thumb|A bathythermograph The bathythermograph, or BT, also known as the Mechanical Bathythermograph, or MBT; is a device that holds a temperature sensor and a transducer to detect changes in water temperature versus depth down to a depth of approximately 285 meters (935 feet). Lowered by a small winch on the ship into the water, the BT records pressure and temperature changes on a coated glass slide as it is dropped nearly freely through the water. While the instrument is being dropped, the wire is payed out until it reaches a predetermined depth, then a brake is applied and the BT is drawn ba

hydroacoustic current meter used to measure water current velocities over a depth range using the Doppler effect

human ability to detect surroundings using sounds

Visable spikes in a sound wave, usally detected for quantizing in music production & more.

system of hydrophones

form of sonar using post-processing of sonar data

device that generates controlled seismic energy used to perform both reflection and refraction seismic surveys

type of sonar that is used to map the seabed