Infrared countermeasure

This article is about missile counter measures. For IRCMonitor, see Wikipedia:IRCMonitor.

Sukhoi Su-27 Flanker shoots off false heat targets

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.

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.

Infrared missile seeker technology

See also: Infrared homing

Infrared missile seekers of the first generation typically used a spinning reticle with a pattern on it that modulates infrared energy before it falls on a detector (A mode of operation called Spin scan). 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. In more recent designs the missile optics will rotate and the a rotating image is projected on a stationary reticle (a mode called Conical scan) or stationary set of detectors which generates a pulsed signal which is processed by the tracking logic. Most shoulder launched (MANPADS) systems use this type of seeker, as do many air defense systems and air to air missiles (for example the AIM-9L).

IRCM principles

A ALQ-144 modulated IRCM jammer.

Infrared seekers are designed to track a strong source of infrared radiation (usually a jet engine in modern military aircraft). IRCM systems are based on modulated source of infrared radiation with a higher intensity than the target. When this modulated radiation 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.

The modulated radiation from the IRCM generates a false tracking command in the seeker tracking logic. The effectiveness of the IRCM is determined by the ratio of jamming intensity to the target (or signal) intensity. this ratio is usually called the J/S ratio. Another important factor is the modulation frequencies which should be close to the actual missile frequencies. For spin scan missiles the required J/S is quite low but for newer missiles the required J/S is quite high requiring a directional source of radiation (DIRCM)..

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.

DIRCM

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. Countermeasure success depend on threat's tracking techniques and requires threats' analysis capabilities . Defeating advanced tracking systems requires a higher level of DIRCM power. Issues of Laser Safety are also taken into account.

Israel has announced a program to develop a system called Multi Spectral Infrared Countermeasure (MUSIC) that will similarly use active lasers instead of flares to protect civilian aircraft against MANPADs. The US Army is deploying a similar system to protect its helicopters..

CIRCM will be a laser based IR countermeasures solution against current and future IR threat systems for the US Army rotorcraft & fixed wing platforms and US Navy and US Air Force rotorcraft platforms.

Flares

Flares create infrared targets with a much stronger signature than the aircraft's engines. The flares provide false targets that cause the missile to make incorrect steering decisions. The missile will rapidly break off a target lock-on.

Fielded examples

Typical IRCM systems are the:

• AN/AAQ-24 by Northrop Grumman - DIRCM.
• 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.
• AN/ALQ-157 by BAE Systems, used for larger helicopters and aircraft.
• Flight Guard by Israel Aerospace Industries, used in military and civilian aircraft (gain the nickname of "Live Saver" due to history of success in saving air vehicles during battles at several countries) , but banned at several European airports. According to defense sources in Israel, the European ban is "odd and based mostly on a misunderstanding
• CAMPS by Saab Avitronics, used for civilian and VIP aircraft.

See also

• Infrared signature
• Countermeasure
• Flare (countermeasure)
• Chaff (radar countermeasure)
• Electronic countermeasures
• Anti-aircraft
• Anti-ballistic missile