sound sensor

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, so called target acquisition.
The same methods can also be used to direct artillery fire at a position with known coordinates, so called fire control.
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 a sensor post, consisting of at least a pair of microphones, to produce a bearing to the source of the sound. When using a number of sensor posts, 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 located in each of these sensor posts.
Typically, the sensor posts have three microphones placed in a triangular shape, typical size around 10 meters, a distance needed to obtain optimal signal to noise ratio in the lower frequency range.
Since 2018, a new approach is being developed, using socalled Acoustic Multi Mission Sensors, that contain both microphones and particle velocity sensors.
As the particle velocity sensors have broad banded directionality, also for lower frequencies, the large (ground based) sensor post can be shrunk to the size of a "molehill".

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