Profs design AK47-locating 'smart dust' helmets
Satnav network node-lids backtrack bullets, ID weapons
Acoustic gunshot detectors have become common in the past few years, and some have been reduced in size to where a single soldier can wear one on his uniform and be cued-in to an enemy's location as soon as he fires.
Engineers in Tennessee, however, are touting the idea of tieing a unit of footsoldiers' acoustic shot-spot sensors together in a wireless net. They think this would offer several benefits: the system wouldn't be confused by echoes or multiple enemies firing at once, and it would be able to locate gunmen who weren't in line-of-sight from an individual soldier. Perhaps even more impressively, the networked sonic system is able to distinguish the calibre of weapons fired, and even in some cases identify different weapons firing the same kind of ammunition.
Vanderbilt University's inhouse Exploration mag reported last week on the gunshot-locator net developed by the uni's Institute for Software Integrated Systems (ISIS). It involves mounting a small electronics package on each soldier's helmet, running on four AA batteries.
In each package is a wireless network node, of a type dubbed a "smart-dust mote" for its small size and cheapness. There are also four separated microphones, for picking up the acoustic signatures of flying bullets, and a GPS satnav location system. The GPS isn't accurate enough to act as a basis for properly pinning down opposing gunmen, so the Vanderbilt boffins added a crafty radio interferometry enhancement system of their own - apparently of such cunning that it has attracted as much interest as the rest of the system on its own.
The system works by picking up the distinctive conical shockwave trailing behind a passing supersonic bullet - the same phenomenon which produces a sonic boom behind a plane at Mach 1+. This is then related to the muzzle blast from the weapon which fired it, trailing slightly behind (the two noises are heard by people under fire as "crack-thud", or "crack-bang"). A software algorithm in the unit can work out a range and bearing to the enemy weapon's muzzle.
So far, so ordinary: a system much like the Qinetiq-America "Ears " or others already under trial with US forces.
But then various special sauces developed by ISIS prof Akos Ledeczi  and his team kick in. All the smart-dust node hats in the squad or platoon net pass their information back and forth, and a special patented filter strips out false muzzle-blast reports - the great bugbear of such technology. The supersonic bullet-booms are very distinctive, it seems, but the muzzle blasts are much harder to distinguish from random banging sounds or echoes - especially with lots of guns firing at once in a built-up area.
As every node has a good idea exactly where it is, owing to its embedded radio-interferometry-enhanced GPS, the combined reports can thus be boiled down to locate all the guns firing nearby within a metre or two - enough to pinpoint which window, corner or whatever each enemy is shooting from. Apparently it still works even in the case of crafty snipers lurking well back from windows - the usual method favoured by the pros. Nor is the system bothered by guns firing out of line of sight - hidden behind walls or buildings or whatever.
"This is the AK-47 assault rifle, the preferred weapon of your enemy. It makes a very distinctive sound"
The nifty software can also reliably identify the calibre of all the flying bullets; and can even, in many cases, tell exactly what kind of gun fired them. It can reliably distinguish NATO 5.56mm rounds shot out of an M16 rifle from ones thrown by an M4 carbine, for instance. However, it can't separate M4s from M249 light machine guns - though the designers think it might be able to in future. Rather more importantly, it can easily tell an AK47 assault rifle  - the weapon most commonly used to shoot at Western soldiers - from anything else, even a US-issue M240 firing ammo of the same 7.62mm calibre*.
Every node is also equipped with Bluetooth short-range data radio, for the purpose of sending the info to a display and interface. Ledeczi and his colleagues suggest that this might be a PDA or similar handheld gadget, but it ought to be possible to make the system work with a hands free heads-up display such as that included in the Land Warrior wearable soldier-smartphone rig. A helmet fitted with Ledeczi's system already knows exactly where it is and how it is oriented with respect to the gun muzzles, so it should be able to mark the positions of enemy shooters on a see-through visor or monocle without difficulty.
Squad leaders or platoon commanders, meanwhile, might rather see their enemies on a map or aerial photograph. Exploration quotes retired US army colonel Albert Sciarretta, now working as a Pentagon assessor, as saying that:
“A leader can use the information that this system provides to react tactically to enemy shooters in ways that limit the number of friendly force and non-combatant casualties. The ISIS system could be easily developed into an operational war-fighting system.”
The kit's even cheap: Ledeczi say that each set would cost only $1,000, as compared to existing systems selling for ten times as much. But nonetheless it seems to be stalled at present - nothing further has happened since trials on an Army range in 2007.
That may be because there are already a lot of competing acoustic gunshot spotters out there; it may be that the ISIS kit isn't actually all that great; there could also be concerns regarding available wireless spectrum, or enemy electronic tinkering. There's also a lot of interest these days in laser scanners which could detect the lenses of enemy snipers' telescopic sights before they had even fired.
Even so, you'd think that the light weight of the ISIS gear and its ability to work in the midst of confused urban gunfights rather than purely against single snipers in line-of-sight mode might make it stand out from the crowd. Its ability to pick out AK47s etc and ignore friendly weapons could even function usefully in avoiding friendly-fire incidents - and help in picking out primary enemy targets like machine guns or heavy sniper rifles. To be sure, it wouldn't work against anyone firing subsonic bullets: but that's pretty rare these days, and slow pistol or submachinegun rounds aren't much threat to well-armoured modern soldiers.
*Not too hard, as NATO 7.62mm is a much higher-powered cartridge than the Soviet 7.62mm used in AKs.
**Ignore the howler "a submachine gun like the AK-47", which seems to have originated with the scribe rather than Ledeczi's crew.