Acoustic location
From The Book of THoTH (Leaves of Wisdom)
Acoustic location is the art and science of using sound to determine the distance and direction of something. This 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 analysed to determine the location of the object in question. This is the principle behind the operation of Sonar.
Passive acoustic location involves the detection of sound or vibration created by the object being detected, which is then analysed to determine the location of the object in question. Acoustic mirrors and dishes, even when using microphones, fall into this category. Typically, more than one device is used, and the location is then triangulated between the several devices.
Acoustic location was used from mid-WW1 to the early years of WW2 for the passive detection of aircraft by picking up the noise of the engines. It was rendered obsolete before and during WW2 by the introduction of radar, which was far more effective.
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Passive locators
Passive locators listen only; they do not emit sound. There are several basic types of passive locator devices
Horn type locators
The general principle of a horn type locator is similar to common 19th century listening enhancement devices, such as ear horns, but scaled up in size. One moderately well know example has become infamous as the Japanese War Tuba, due to the apparent resemblance to the western musical instrument.
Of course, the most well known form of this type of locator is the human ear.
Mirror type locators
A large concrete mirror is used to focus sound on a microphone. Clever design allows for the ability to not only determine range but direction as well.
A few acoustic mirrors still can still be found on the coast of Britain to this day. Such devices are said to have been able to detect aircraft as far away as 20 miles, or more.
Transducers
This involves the direct placement of sensors on solid materials, such as the ground, building walls, etc. By mapping and timing the response of the various sensors, locations of different events can be located inside of different structures. One typical use in the subsonic range is in the mapping of events inside volcanos, as seen in the acoustic cross section on Mount St Helens.[1]
Active 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.
Sonar
SONAR (SOund Navigation And Ranging) — or sonar — is a technique that uses sound propagation under water to navigate or to detect other vessels. There are two kinds of sonar — active and passive. Sonar is a subcategory of acoustic location.
For more information on this item, see the article on Sonar
Echo location
Dolphins and whales are well known for their use of Sonar. Bats are also famous for their use of echo location. For more information of this item, see the article on echo location.
Seismic surveys
Seismic surveys involve the generation of sound waves to measure underground structures. Source waves are generally generated 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.
See also
- Animal echolocation: animals emitting sound waves and listening to the echo in order to locate objects or navigate.
- Human echolocation: the use by blind people of sound to navigate.
- 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 echos to look inside the body
- Seeing with your ears
--Angel 16:22, 5 July 2006 (CDT)
