Acoustic location
Acoustic location is the science of using sound to determine the distance and direction of something. Location can be done actively or passively, and can take place in gases (such as the atmosphere), liquids (such as water), and in solids (such as in the earth).
- Active acoustic location involves the creation of sound in order to produce an echo, which is then analyzed to determine the location of the object in question.
- Passive acoustic location involves the detection of sound or vibration created by the object being detected, which is then analyzed to determine the location of the object in question. (See Sound ranging)
Both of these techniques, when used in water, are known as sonar; passive sonar and active sonar are both widely used.
Acoustic mirrors and dishes, when using microphones, are a means of passive acoustic localization, but when using speakers are a means of active localization. Typically, more than one device is used, and the location is then triangulated between the several devices.
Acoustic location in air was used from mid-World War I[1] to the early years of World War II for the passive detection of aircraft by picking up the noise of the engines. It was rendered obsolete before and during World War II by the introduction of radar, which was far more effective (but interceptable). Acoustics has the advantage that it can 'see' around corners and over hills.
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[edit] Active / passive locators
Active locators have some sort of signal generation device, in addition to a listening device. The two devices do not have to be located together.
[edit] Sonar
SONAR (SOund Navigation And Ranging) — or sonar — is a technique that uses sound propagation under water (or occasionally in air) to navigate, communicate or to detect other vessels. There are two kinds of sonar — active and passive. A single active sonar can localize in range and bearing as well as measuring radial speed. However, a single passive sonar can only localize in bearing directly, though target motion analysis can be used to localize in range, given time. Multiple passive sonars can be used for range localization by triangulation or correlation, directly.
For more information on this item, see the article on Sonar.
[edit] Biological echo location
Dolphins, whales and bats use echolocation to detect prey and avoid obstacles.
[edit] Time-of-arrival localization
Having speakers/ultrasonic transmitters emitting sound at known positions and time, the position of a target equipped with a microphone/ultrasonic receiver can be estimated based on the time of arrival of the sound. The accuracy is usually poor under non-line-of-sight conditions, where there are blockages in between the transmitters and the receivers. [2]
[edit] Seismic surveys
Seismic surveys involve the generation of sound waves to measure underground structures. Source waves are generally created by percussion mechanisms located near the ground or water surface, typically dropped weights, vibroseis trucks, or explosives. Data are collected with geophones, then stored and processed by computer. Current technology allows the generation of 3D images of underground rock structures using such equipment.
For more information, see Reflection seismology.
[edit] Ecotracer
Ecotracer is an acoustic locator that was used to determining the presence and position of ships in fog. Some could detect targets at distances up to 12 kilometers. Static walls could detect aircraft up to 30 miles away.
[edit] Types
There were four main kinds of system:[3]
- Personal/wearable horns
- Transportable steerable horns
- Static dishes
- Static walls
[edit] Impact
American acoustic locators were used in 1941 to detect the Japanese attack on the fortress island of Corregidor in the Philippines.
[edit] References
- ^ How Far Off Is That German Gun? How 63 German guns were located by sound waves alone in a single day, Popular Science monthly, December 1918, page 39, Scanned by Google Books: http://books.google.com/books?id=EikDAAAAMBAJ&pg=PA39
- ^ Chan, Y.T; Tsui, W. Y.,So, H. C. and Ching, P. C. (2006). "Time-of-arrival based localization under NLOS Conditions". IEEE Trans. Vehicular Technology (IEEE Vehicular Technology Society) 55 (1): 17–24. doi:10.1109/TVT.2005.861207. ISSN 0018-9545. http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?tp=&arnumber=1583910&isnumber=33430.
- ^ http://www.aqpl43.dsl.pipex.com/MUSEUM/COMMS/ear/ear.htm
[edit] See also
- Acoustic mirror
- Animal echolocation: animals emitting sound waves and listening to the echo in order to locate objects or navigate.
- Human echolocation: the use of echolocation by blind people.
- Acoustic wayfinding: the practice of using auditory cues and sound markers to navigate indoor and outdoor spaces.
- Sonar: (sound navigation and ranging) the use of sound to navigate or to locate other watercraft, usually by submarines.
- Echo sounding: listening to the echo of sound pulses to measure the distance to the bottom of the sea, a special case of Sonar.
- Medical ultrasonography: the use of ultrasound echoes to look inside the body.
- Sensory substitution.
- Japanese war tuba: 1930s Japanese acoustic locator.
- Sound localisation.
[edit] External links
- An introduction to Acoustic Holography.
- "Huge Ear Locates Planes and Tells Their Speed" Popular Mechanics, December 1930 article on French aircraft sound detector with photo.
