Detection and Warning Systems
Missiles rely on several forms of guidance exploiting radar and laser, Infrared (IR) and visible light. Guidance using physical light can be frustrated or degraded through camouflage. This can make the target difficult, if not impossible, to see. Even if a target is visible the type of camouflage used could make it difficult to discern the target’s range relevant to the missile’s firing position, its speed or trajectory. All these factors could hamper adequate fire control to ensure the missile reaches its target.
Unlike weapons using visual guidance radar, laser and thermal guidance systems must be countered electronically. Firstly the incoming weapon must be detected. This is done with optronic systems which see the weapons’ visual silhouette as it approaches. Sensors may also use thermal imaging to detect the heat signature from the missile’s hot exhaust. A radar will detect and track the weapon using radio waves transmitted from the radar’s antenna. Other warning systems detect the laser light of a laser-guided missile. Some warning systems only provide the bearing of the threat relative to one’s own position. Others provide a precise position of the incoming missile relative to the sensor. This range of sensors equip an array of military platforms like warships, vehicles and aircraft.
Visible and IR light, and radio waves, all inhabit parts of the electromagnetic spectrum. Visible light uses frequencies of circa 400 terahertz/THz to 800THz. IR is further down the spectrum at frequencies of 300 gigahertz to 400THz. Finally, the radio spectrum is lowest down of all going from three hertz to three terahertz. Laser light also falls within the electromagnetic spectrum. As all these mediums exploit the spectrum, and electromagnetic techniques are used in several ways against them as countermeasures.
Electronic Countermeasures (ECMs) attack radar-guided weapons, radar in general and are examined elsewhere in the ‘Jamming Devices/Jammers’ section. Broadly speaking, ECMs use two different techniques: Jamming will seek to hide the target from the radar by placing it behind a curtain of electromagnetic interference. Alternatively, it will distract or seduce the radar by generating jamming in such a way as to present either a false or more tempting target to the radar.
IR and laser-guided weapons are countered with different techniques. An IR-guided weapon uses heat produced by the target as a guidance point. This could be an armoured vehicle’s engine, a military aircraft’s hot exhaust, the exhausts of a warship or other heat sources above the water. IR weapons are countered by producing a hotter heat source to distract or blind the missile’s seeker. Hot flares are projected between the target and the missile. Alternatively some countermeasures use a laser aimed directly into the missile’s IR guidance system which burns out the sensor blinding the missile.
Laser-guided weapons are amongst the hardest to counter. One technique involves using vapour or smoke to block the laser from its target. The rationale is to disperse such contaminants into the atmosphere between the target and the missile. The contaminants exploit a phenomenon called attenuation by which they absorb and disperse laser light away from the target. Smoke countermeasures have the added benefit of obscuring the target in the visible spectrum. An armoured vehicle under attack could disperse a cloud of smoke and manoeuvre into a safe space behind it. Atmospheric effects like wind can impinge on the dispersion and duration of the smoke.
Nonetheless, advanced manufacturing techniques ensure smoke remains concentrated for as long as needed. While smoke is practical for use in land and maritime environments, the speeds at which aircraft travel make it an impractical countermeasure. To this end, aircraft under attack from a laser-guided weapon often have little choice but to try and manoeuvre away from the threat and cause the missile to lose lock.