Passive acoustics is the action of listening for sounds, often at specific frequencies or for purposes of specific analyses. As applied to underwater acoustics, also termed hydroacoustics or

sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances ( ranging), communicate with or detect objects on ...

, passive acoustics can be used to listen for

underwater explosion An underwater explosion (also known as an UNDEX) is a chemical or nuclear explosion that occurs under the surface of a body of water. While useful in anti-ship and submarine warfare, underwater bombs are not as effective against coastal facilities. ...

earthquakes An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...

, volcanic eruptions, sounds produced by fish and other animals, vessel activity or aquatic detecting equipment (as in hydroacoustics to track fish).

References

* David A. Mann, Anthony D. Hawkins, and J. Michael Jech
Active and Passive Acoustics to Locate and Study Fish
from book Fish Bioacoustics: With 81 Illustrations (pp.279-309), April 2008 * Marco Brunoldi, Giorgio Bozzini, et al.
A Permanent Automated Real-Time Passive Acoustic Monitoring System for Bottlenose Dolphin Conservation in the Mediterranean Sea
2016 Ichthyology {{acoustics-stub