A countermeasure is a system (usually for a military application) designed to prevent sensor-based weapons from acquiring and/or destroying a target.
Countermeasures that alter the electromagnetic, acoustic or other signature(s) of a target thereby altering the tracking and sensing behavior of an incoming threat (e.g., guided missile) are designated softkill measures.
Measures that physically counterattack an incoming threat thereby destroying/altering its payload/warhead in such a way that the intended effect on the target is majorly impeded are designated hardkill measures.
Softkill measures are applied when it is expected that a sensor-based weapon system can be successfully interfered with. The threat sensor can be either an artificial one, e.g., a solid-state infrared detector
, or the human sensory system (eye and/or ear).
Softkill measures generally interfere with the signature of the target to be protected. In the following the term signature refers to the electromagnetic signature of an object in either the ultraviolet (wavelength: 0.3-0.4 µm), visual (0.4-0.8 µm), or infrared (0.8 - 14 µm) spectral range as well as cm-radar range (frequency: 2-18 GHz), mmw-radar (35, 94, 144 GHz) and finally sonar range (either 50Hz - 3 kHz and/or 3- 15 kHz).
One or more of the following actions may be taken to provide softkill:
- Reduction of signature
- Augmentation of signature
Softkill countermeasures can be divided into on-board and expendable countermeasures.
Whereas on-board measures are fixed on the platform to be protected, expendable measures are ejected from the platform.
Preemptive action of countermeasures is directed to generally prevent lock-on of a threat sensor to a certain target. It is based on altering the signature of the target by either concealing the platform signature or enhancing the signature of the background, thus minimizing the contrast between the two.
Reactive action of countermeasures is directed toward break-lock of a threat already homing in on a certain target. It is based on the tactics of signature imitation, augmentation, or reduction.
Generally one has to distinguish between infrared and radar countermeasures. the wavelength range between 0.8 and 5 µm is considered as Infrared
(IR), The frequency range between 2 and 18 GHz is considered as Radar
In the wake of shoulder-launched missile attacks against civilian passenger and cargo airliners in the early 2000s, various agencies investigated the feasibility of equipping countermeasures chaff and flares. Many commercial carriers found the estimated price of countermeasures to be too costly. However, the Israeli airline El-Al, having been the target of the failed 2002 airliner attack, in which shoulder-launched surface-to-air missiles were fired at an airliner while taking off, began equipping its fleet with radar-based, automated flare release countermeasures from June 2004. This caused concerns in some European countries, regarding the possible fire hazard at civilian airports, resulting in banning such aircraft from landing at their airports. In 2007, Saab announced a new infrared countermeasure system called CAMPS that does not use pyrotechnic flares, thereby directly addressing these concerns.
IR-decoy flares serve to counter infrared-guided surface-to-air missiles (SAM) or air-to-air missiles (AAM) and can be expelled from a craft according to an anticipated threat in defined sequences.
To counter radar-guided missiles, chaff is used. These are copper nickel-coated glass fibers or silver-coated nylon fibers having lengths equal to half of the anticipated radar wavelength.
Land and sea-based forces can also use such countermeasures, as well as smoke-screens
that can disrupt laser
ranging, infrared detection, laser weapons, and visual observation.
Except for countering ICBMs, hardkill measures generally refer to measures taken in the so-called "end-game
" shortly before a warhead/missile hits its target.
The hardkill measure in general physically affects the incoming warhead/missile by means of either blast and/or fragment action.
The action may lead to:
- disturbance of the stability of a kinetic energy penetrator which in turn will greatly lose its penetration ability as the deflection angle increases.
- premature initiation of a shaped charge (e.g., too great stand-off), but most likely improper initiation, thereby impeding optimum jet development.
- destruction of the airframe of an inbound missile or shell.
An example of a Hardkill countermeasure is the reactive armour found on many modern armoured vehicles.
Another example of hardkill countermeasures is the use of short-range missiles or rapid-fire guns to protect warships
and fixed installations from cruise missile, bomb and artillery attacks.
Intercontinental ballistic missiles (ICBMs)
Countermeasures are a complicating factor in the development of anti-ballistic missile
defense systems targeting ICBMs
. Like aircraft, ICBMs theoretically could evade such systems by deploying decoys
in the midcourse phase of flight. Novel proposed chaff mechanisms describe the creation of a "threat cloud" by deploying large aluminized PET film balloons
which could conceal a warhead among a large number of inert objects having similar radar profiles.