Active acoustics
Encyclopedia
Active Acoustics is a means of measuring the range to an object and its relative size by producing a pulse of sound
and measuring the time it takes for an echo
to return from the object and the amplitude
of the returned echo. The range is calculated as a function of the speed of sound and the time it takes for the echo to return.
Active acoustics is the principle behind SONAR
or hydroacoustics
for underwater measurements.
Active acoustic split-beam systems are capable of detecting organisms as small as krill, with no limit on upper sizes. Fish position within the ensonified beam can be accurately located in split-beam systems, allowing calculation of target strength, swim speed, and direction of movement. New directions for active acoustics in science include multibeam, multi-frequency, and high frequency imaging systems. While traditional systems have a beam width of 7-12 degrees sampling a slice of the water column, Multibeam systems such as the EM3002 can be used to examine school shape and behavior with a 130 degree beam width. In addition, multibeam systems are used for details bathymetric mapping and bottom typing based on the returned echo from the bottom. By using multiple frequency systems, fish of varying sizes can be differentiated due to resonance frequencies. High frequency systems such as the DIDSON provide camera-like accuracy of targets in the water column or on the bottom.
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
and measuring the time it takes for an echo
Echo (phenomenon)
In audio signal processing and acoustics, an echo is a reflection of sound, arriving at the listener some time after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room and an empty room. A true echo is a single...
to return from the object and the amplitude
Amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
of the returned echo. The range is calculated as a function of the speed of sound and the time it takes for the echo to return.
Active acoustics is the principle behind SONAR
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
or 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...
for underwater measurements.
Active acoustic split-beam systems are capable of detecting organisms as small as krill, with no limit on upper sizes. Fish position within the ensonified beam can be accurately located in split-beam systems, allowing calculation of target strength, swim speed, and direction of movement. New directions for active acoustics in science include multibeam, multi-frequency, and high frequency imaging systems. While traditional systems have a beam width of 7-12 degrees sampling a slice of the water column, Multibeam systems such as the EM3002 can be used to examine school shape and behavior with a 130 degree beam width. In addition, multibeam systems are used for details bathymetric mapping and bottom typing based on the returned echo from the bottom. By using multiple frequency systems, fish of varying sizes can be differentiated due to resonance frequencies. High frequency systems such as the DIDSON provide camera-like accuracy of targets in the water column or on the bottom.
See also
- Fisheries AcousticsFisheries acousticsFisheries acoustics includes a range of research and practical application topics using acoustical devices as sensors in aquatic environments. Acoustical techniques can be applied to sensing aquatic animals, zooplankton, and physical and biological habitat characteristics.-Basic Theory:Biomass...
- HydrophoneHydrophoneA hydrophone is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure change...