Infrared countermeasures
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Infrared countermeasures (IRCM) are devices designed to protect aircraft from infrared homing ("heat seeking") missiles by confusing the missiles' infrared guidance system so that they will miss their target.
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[edit] History
First deployed during the Vietnam War, they have been enhanced over the years to be lighter, more portable, and more reliable, but the basic principle is the same.
[edit] Infrared missile seeker technology
- See also: Infrared homing
Infrared missile seeker technology typically uses a spinning reticle with a pattern on it that modulates infrared energy before it falls on a point source detector. The patterns used differ from seeker to seeker, but the principle is the same. By modulating the signal, the steering logic can tell where the infrared source of energy is relative to the missile direction of flight. Most shoulder launched (MANPADS) systems use this type of seeker, as do many air defense systems.
[edit] IRCM principles
IRCM systems are designed around a strong source of infrared energy (originally gas flames, which wasn't the safest design in the world for an aircraft system). The energy is then modulated within the equipment. When this modulated energy is seen by a missile seeker, it overwhelms the modulated signal from the aircraft and provides incorrect steering cues to the missile. The missile will begin to deviate (wobble) from the target, rapidly breaking lock. Once an infrared seeker breaks lock (they typically have a field of view of 1 - 2 degrees), they rarely reacquire the target. By using flares, the target can cause the confused seeker to lock onto a new infrared source that is rapidly moving away from the true target.
[edit] Drawbacks of IRCM
One of the drawbacks of standard IRCM systems is that they broadcast a bright source of infrared. If the modulation of the signal is not effective against a particular seeker system, the IRCM will enhance the ability of the missile to track the aircraft. The aircrews typically brief about potential threats and choose an IRCM modulation that will be effective against likely threats.
[edit] Alternatives and advanced systems
More advanced systems, called DIRCM, or Directional Infrared Countermeasures, avoid this potential drawback by mounting the energy source on a moveable turret (much like a FLIR turret). They only operate when cued by a missile warning system of a missile launch, and use the missile plume to accurately aim at the missile seeker. The modulated signal can then be directed at the seeker, and the modulation scheme can be cycled to try to defeat a variety of seekers.
[edit] Fielded examples
Typical IRCM systems are the:
- AN/ALQ-132 by Sanders/BAE Systems. Used in the 1960s in Vietnam, and was a fuel fired flashlamp system.
- AN/ALQ-144 by BAE Systems, used for helicopter defence. A PDF Brochure is available from BAE
- AN/ALQ-157 by BAE Systems, used for larger helicopters and aircraft.
