John F. Kennedy, Martin Luther King and Zoran Djindjic are only three well known victims killed by snipers. However, killers firing from behind have cost a much larger number of people their lives since the invention of the rifle. Individuals are not always the target. Sniper fire from covert locations is often deployed in order to achieve questionable goals. For example, in the Bosnian War, Bosnian-Serb paramilitary deployed sharp shooters to demoralize residents of Sarajevo and to force the surrender of the city. Gaddafi’s snipers in Bengasi and Misrata likely had similar interests in mind.
In addition to such attacks, where victims are generally located outdoors and are unprotected, people in vehicles are also fired at. A single hit could, under certain circumstances, prove fatal for all passengers. The same applies for aircraft flights. Helicopters in action are often fired upon with barrel weapons. If none of the critical components or passengers is hit, the attack can often only be recognized after landing. Although active protection against such attacks is currently nothing more than dreams of the future, immediate detection of such attacks combined with specification of direction would be a significant component for increasing security – risks could be bypassed, areas could be flown around, cover could be taken in the right place.
Example for muzzle flash - Images: Wikipedia (public domain)
For nearly two decades now, many countries have been working diligently on developing warning devices of the type described. Generally speaking, there are several ways to detect a shot or projectile. If rifles are used, the explosion that propels the projectile produces a blast wave. Microphones can be used to measure such blast waves. Radar technology also permits detection if the projectile is large enough. The trajectory can be determined. The muzzle flash produced by the explosion can also be detected with electro-optical detectors. If adequate optical resolution is available, the projectile itself can also be tracked along its trajectory.
The increase in asymmetrical or terrorist threats in the last decade and the resulting, urgent need has led to the early deployment of devices for detecting rifle fire on an operational level, which have only just completed the test phase. The United States and Great Britain in particular actively deployed such technology in Iraq and Afghanistan. These warning systems are also being used by US communities to an increasing extent. Cities like Pittsburgh, Newark or Dallas have already set up warning systems in city districts particularly at threat or they are in planning.
However, the devices are still not functioning in a really satisfactory manner. Most of the systems in use function based on the detection principle of acoustic positioning. Particularly in an urban environment, this is not trivial as, among other things, reflections of the sound wave against buildings may cause confusion and thus result in errors when determining the firing position.
The expansion of a warning system that functions on a purely acoustic basis in order to accommodate an extra electro-optical component may be the solution needed for exact determination of the direction of fire. In an initial step, a basic implementation for a warning system is being worked on at the IOSB, which reliably detects the muzzle flash with electro-optical sensors. Studies to date have returned positive results with respect to the use of sensors that function in the infrared spectral range. A high sampling rate could also contribute to the reduction of false alarm rates as the temporal signature of the momentary moment of firing can be analyzed.
Another problem, which has not yet been resolved, is the realization of the panorama view, which is required on an operational level. While a microphone picks up sound waves from all directions, the visual field of view of an optical sensor is in most cases very restricted. For this reason, more than one sensor must be used in order to guarantee widespread coverage. Various disadvantages are associated with this, e.g. increased energy consumption and an increase in size and weight. The IOSB is currently working on and testing approaches and ideas for solving this problem. The next logical step involves work to merge acoustics and optronics in order to offer civil and military users a warning system that functions reliably.