Sound ranging

In land warfare, artillery sound ranging is a method of determining the coordinates of a hostile 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.

It is an application of sound (or acoustic) location, which is location of the source of sounds that may originate in the air, on the ground or on or below the water's surface. Sound ranging was one of three methods of locating hostile artillery that rapidly developed in World War I. The others were aerial reconnaissance (visual and photographic) and flash spotting.

A sound ranger used aural and stop-watch methods which first 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 person 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 was quickly discarded as ineffective by the western allies, who 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.

A scientific method of sound ranging system requires the following equipment.

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 midway between the two microphones. The intersection of at least three bearings 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 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.

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