hydrofone

A hydrophone (sometimes spelled hydrofone) is an underwater acoustic sensor that converts sound waves in water into electrical signals. It functions as a microphone adapted to the acoustic and pressure environment of aquatic media, enabling detection, measurement, and recording of underwater sound.

Hydrophones typically use piezoelectric materials, which generate voltage under mechanical stress from pressure fluctuations, though other technologies such as fiber‑optic and electromagnetic transducers are also used. Designs vary from omnidirectional elements to directional arrays; single hydrophones serve simple listening tasks, while arrays support beamforming, localization, and signal enhancement.

Applications include marine biology (recording vocalizations of mammals, fish, and invertebrates), naval and defense uses (passive sonar, submarine detection), seismic and geophysical surveys, underwater engineering and monitoring (cable and pipeline inspection, noise assessment), and acoustic communication with autonomous underwater vehicles. Hydrophones are deployed in a range of platforms: moorings, towed arrays, seafloor observatories, buoys, and vehicles.

Performance depends on sensitivity, frequency response, self-noise, and environmental factors such as temperature, salinity, and flow noise. Calibration against known sound sources is important for quantitative measurements. Limitations include susceptibility to flow noise and biofouling, and the need for pressure-resistant housings at depth.

Etymologically, the term combines Greek hydro‑ (water) and phonē (sound). Hydrophones are central tools in underwater acoustics and oceanographic research.