Hydrophone

A hydrophone is an underwater microphone, a piezoelectric transducer that converts acoustic pressure in water to a voltage. Most use piezoceramics such as lead zirconate titanate and report sensitivity in dB re 1 V per microPa, typically around minus 160 to minus 200 dB, flat across bands from a few hertz to over 100 kHz. Single hydrophones record ambient noise and marine-mammal calls; arrays add directionality and beamforming for passive sonar and seismic surveys. Calibrated hydrophones underpin underwater-noise monitoring under standards such as ISO 18405, and bottom-moored units anchor long-term soundscape records.