Passive acoustics
Encyclopedia
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
, passive acoustics can be used to listen for underwater explosion
s, earthquakes, volcanic eruptions, sounds produced by fish and other animals, vessel activity or aquatic detecting equipment (as in hydroacoustics
to track fish).
Hydroacoustics may be one of the most misunderstood techniques for fisheries research. In essence, hydroacoustics monitoring is based on a few relatively simple principles. An acoustic echo sounder transmits a pulse of acoustic energy into the water. The pulse of energy travels through the water at a speed of approximately 1500 m/s. When the acoustic pulse encounters an object, such as a fish or the bottom, some of the energy (i.e. an echo) is reflected back to the transducer. The echo sounder amplifies the received signal and then sends it to an output device (such as a chart recorder or video display) and digital echo processor.
As applied to underwater acoustics, also termed hydroacoustics
Hydroacoustics
Hydroacoustics is a general term for the study and application of sound in water. The term comes from Greek υδρο, water, and ακουστική, acoustics...
or SONAR
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
, passive acoustics can be used to listen for underwater explosion
Underwater explosion
An underwater explosion, also known as an UNDEX, is an explosion beneath the surface of water. The type of explosion may be chemical or nuclear...
s, earthquakes, volcanic eruptions, sounds produced by fish and other animals, vessel activity or aquatic detecting equipment (as in hydroacoustics
Hydroacoustics
Hydroacoustics is a general term for the study and application of sound in water. The term comes from Greek υδρο, water, and ακουστική, acoustics...
to track fish).
Hydroacoustics may be one of the most misunderstood techniques for fisheries research. In essence, hydroacoustics monitoring is based on a few relatively simple principles. An acoustic echo sounder transmits a pulse of acoustic energy into the water. The pulse of energy travels through the water at a speed of approximately 1500 m/s. When the acoustic pulse encounters an object, such as a fish or the bottom, some of the energy (i.e. an echo) is reflected back to the transducer. The echo sounder amplifies the received signal and then sends it to an output device (such as a chart recorder or video display) and digital echo processor.