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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. 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. As a military air defense tool, passive acoustic location was used from mid-World War I〔''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〕 to the early years of World War II to detect enemy aircraft by picking up the noise of their engines. It was rendered obsolete before and during World War II by the introduction of radar, which was far more effective (but interceptable). Acoustic techniques had the advantage that they could 'see' around corners and over hills, due to sound refraction. The civilian uses include locating wildlife〔(【引用サイトリンク】url=http://www.greeneridge.com/projects.html )〕 and locating the shooting position of a firearm. == Military use == Military uses have included locating submarines and aircraft. The first use of this type of equipment was claimed by Commander Alfred Rawlinson of the Royal Naval Volunteer Reserve, who in the autumn of 1916 was commanding a mobile anti-aircraft battery on the east coast of England. He needed a means of locating Zeppelins during cloudy conditions and improvised an apparatus from a pair of gramaphone horns mounted on a rotating pole. Several of these equipments were able to give a fairly accurate fix on the approaching airships, allowing the guns to be directed at them despite being out of sight.〔Rawlinson, Alfred (1923), (Rawlinson, ''The Defence of London'', Andrew Melrose, London & New York, pp.110-114 )〕 Although no hits were obtained by this method, Rawlinson claimed to have forced a Zeppelin to jettison its bombs on one occasion.〔Rawlinson, pp. 118-119〕 The air-defense instruments usually consisted of large horns or microphones connected to the operators' ears using tubing, much like a very large stethoscope.〔(【引用サイトリンク】accessdate=2006-06-01 )〕〔(【引用サイトリンク】title=Photo of Sound Locator )〕 Most of the work on anti-aircraft sound ranging was done by the British. They developed an extensive network of sound mirrors that were used from World War I through World War II. Sound mirrors normally work by using moveable microphones to find the angle that maximizes the amplitude of sound received, which is also the bearing angle to the target. Two sound mirrors at different positions will generate two different bearings, which allows the use of triangulation to determine a sound source's position. As World War II neared, radar began to become a credible alternative to the sound location of aircraft. For typical aircraft speeds of that time, sound location only gave a few minutes of warning.〔 The acoustic location stations were left in operation as a backup to radar, as exemplified during the Battle of Britain. Today, the abandoned sites are still in existence and are readily accessible.〔 After World War II, sound ranging played no further role in anti-aircraft operations. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Acoustic location」の詳細全文を読む スポンサード リンク
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