Sound ranging

In land warfare, sound ranging is a method of determining the coordinates of a hostile artillery battery using data derived from the sound of its guns (or mortar or rockets) firing. The same methods can also be used to direct artillery fire at a position with known coordinates.

Sound ranging is sometimes confused with sound locating, which is a collection of techniques used to locate the source of other sounds that may originate in the air, on the ground or on or below the sea's surface. This entry is primarily concerned with sound ranging. Sound ranging was one of three methods of locating hostile artillery that rapidly developed in World War I. The others were air reconnaissance (both visual and photographic) and flash spotting.

Sound ranging using aural and stop-watch methods had emerged before World War I. Stop-watch methods involved spotting a gun firing, measuring the bearing to it and the length of time it took the sound to arrive. Aural methods typically involved a man listening to a pair of microphones a few kilometres apart and measuring the time between the sound arriving at the microphones. This method appears to have been used by the Germans throughout that war, but were quickly discarded as ineffective by the western allies. These allies developed scientific methods of sound ranging whose descendants are still used.

The basis of scientific sound ranging is to use pairs of microphones to produce a bearing to the source of the sound. The intersection of these bearings gives the location of the battery. The bearings are derived from the differences in the time of arrival at the microphones.

Background

Basic equipment setup

A scientific method of sound ranging system requires the following equipment.
* An array of 4 to 6 microphones extending several kilometres
* A system capable of measuring the sound wave arrival time differences between the microphones.
* A means of analyzing the time differences to compute the position of the sound source.

The basic method is to use microphones in pairs and measure the difference in the time of arrival of a sound wave at each microphone in the pair (inner microphones are members of two pairs). From this a bearing to the origin of the sound can be found from the point mid-way between the two microphones. The intersection of at least 3 bearing will be the location of the sound source.

Figure 1 illustrates the basic system.

Some systems may not allow arbitrary placement of the microphones. For example, they may require the [http://www.photolib.noaa.gov/historic/c&gs/theb2916.htm microphones to be placed on a straight line] . These constraints would be imposed to simplify the calculation of the artillery position and are not a characteristic of the general approach.

The microphones also may be designed to pick up only the sound of the gun firing. There are three types of sounds that can be picked up by the microphone.
* the gun firing (the desired signal)
* the sound of the shell moving through the air
* the impact of the shell

During World War I it was discovered that the gun firing makes a low rumbling sound that is best picked up with a microphone that is sensitive to low frequencies and rejects high frequencies.] The civilian uses include locating wildlife] As World War II neared, radar began to become a credible alternative to the sound ranging of aircraft. However, the sound ranging stations were left in operation as a backup to radar.cite news|url=http://www.gmtgames.com/living_rules/TBB_Scenarios.pdf|author=Lee Brimmicombe Woods|publisher=GMT Games LLC|title=The Burning Blue: The Battle of Britain 1940|date=7 December 2005|format=PDF]

While sound ranging for artillery spotting had a secure place during the war, aircraft spotting proved less useful. During the Battle of Britain, sound ranging was used as a backup for radar in locating inbound aircraft.cite news|url=http://www.gmtgames.com/living_rules/TBB_Scenarios.pdf|author=Lee Brimmicombe Woods|publisher=GMT Games LLC|title=The Burning Blue: The Battle of Britain 1940|date=7 December 2005|format=PDF] Since aircraft in World War II were much faster than in World War I, aircraft sound ranging only gave a few minutes of warning.cite news|url=http://www.design-technology.info/inventors/page29.htm|author=W.Richmond|year=2003|title=Before RADAR - Acoustic Detection of Aircraft] This made it a much less attractive approach than radar. 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.

Because the cost of the associated sensors and electronics is dropping, the use of sound ranging technology is becoming accessible for other uses, such as for locating wildlife.cite journal|author=John L. Spiesberger|month=June | year=2001|volume=109|issue=6|journal=The Journal of the Acoustical Society of America|title=Hyperbolic location errors due to insufficient numbers of receivers|pages=3076–3079|doi=10.1121/1.1373442]

The US government has been showing interest in using sound ranging to determine the location of gunfire in large cities.

Notes