2009/03/24

Acoustic sniper detection systems and their weak spot

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The detection of snipers is a terribly difficult affair and became an art of camouflage, patience, deception, caution and optics during the First World War.

Snipers haven't evolved much since that time - their camouflage got only a little bit better, their optics became much better and the weapons became a bit better. The difference between a good Great War sniper and a modern sniper is negligible at up to 400 m distance, though.
True snipers are rare outside of regular armies. More often it's just some guy who has a scoped rifle and enough self-preservation instinct to use camouflage and withdrawal. Even normal rifles without scopes can be used for sniping - the Finns demonstrated their deadliness in this during 1939/40.

Detecting snipers / sharpshooters / marksmen is an important capability. We ignored that (and sniping in general) in our WW3 planning, but the small wars and expeditions since 1991 re-emphasized the importance of sniping.

Technological aids have been introduced to detect snipers after they had shot for the first time (earlier detection is simply a matter of tactics, intelligence, observation and normal sensors).

The most successful technical principle in use is apparently based on triangulating the sonic boom of rifle bullets. The technology is relatively similar to the artillery sound ranging since about 1916, radio direction finding, radar receiver, sonar receiver and passive radar warning/direction finding.

Several microphones (antennas) sense the acoustic shockwave at different times - a computer can analyze this data to compute the direction, distance, speed and time of the shot.
It's pretty much enough to get a flight profile of the bullet.
This flight profile includes the information about the origin, of course.
The inadequacy of reality limits the accuracy, of course.


Such a system is cheaper and consumes less energy than optical, thermal, ladar or radar sensors. It does not emit like a radar.
It's not focused on the muzzle fire and can thus not be countered by the use of concealment or a suppressor. An acoustic system that relies on the muzzle noise would produce too many false alarms.

There is one remaining weak spot, though: It's very principle.
It depends on the sonic boom of the bullet.
Subsonic bullets don't have that.

The good news for the acoustic sniper detection system user is that subsonic bullets usually suck.

A subsonic 5.56mm bullet would be disappointing even for a pocket pistol.
A subsonic 7.62mm bullet would be adequate for a pocket pistol.
A subsonic special (dense and long) 7.62mm bullet would be adequate for a normal pistol.

Nevertheless, the dependency on the sonic boom may become a problem in the future.

The Russians have developed a family of 9mm weapons using the 9x39 mm calibre with especially heavy bullets. The family included 'assault rifles' and short-range (urban) sniper rifle VSSThese weapons have a surprising capability to penetrate objects and armor (6mm steel at 100 m).

A larger calibre and heavier bullet is the most obvious possibility how to increase performance of a subsonic bullet. Only subsonic bullets are relatively quiet - a suppressor reduces the muzzle noise and eliminates muzzle fire, the bullet itself causes no sonic boom.

The Russians didn't stop at 9x39mm, though. A later step was the 12.7mm "Vychlop" ("Exhaust") rifle. The larger calibre (apparently a special cartridge) allowed for a much heavier and more powerful bullet. 12.7mm is an old Russian calibre for very heavy machine guns.
The astonishing thing about this rifle is its acceptable weight: 7 kg including scope and silencer.
The practical range is likely no more than 300m, though. The bullet is slow and the bullet drop becomes very significant at long ranges. A moving target or a wrong range estimate would cause a miss.

I'm not sure about the exact penetration capability of the 12.7mm subsonic bullet, but level IV vests are likely challenged by such a large bullet - even a subsonic one. The test program for body armour does as far as I know not include tests against very heavy subsonic AP bullets, though.

Sonic boom-based sniper detection systems could be neutralized by the use of subsonic weapons - and dedicated subsonic rifle designs can be quite powerful.

Sven Ortmann
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4 comments:

  1. or what about a bullet with nano materials that won't emit the sonic beam, like the materials used in airplanes that don't reflect the radar wave...

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  2. It's not the bullet that emits the sound, but the fact that it displaces the air.

    This is similar to the thunder created by aircraft going supersonic - extremely difficult to reduce.

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  3. There have been tests to reducing the boom while preserving the speed, but i do not know how viable they are or if it is even possible. not my area of expertise

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  4. Still, it would be worthwile to keep shooting supersonic just to provoke the usage of acoustic detection systems. By military logic they would probably depend on some big unwieldy thing, and troops would be very reluctant to advance in the face of supersonic snipers if there isn't any detection systems. The snipers would need lighter guns though, what with all the running they would be expected to do...

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