Infrared homing refers to a passive missile guidance system which uses the emission from a target of electromagnetic radiation in the infrared part of the spectrum to track it. Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. ( German 'luftvafe is a generic German term for an Air force. IRIS-T ( Infra Red Imaging System Tail/Thrust Vector-Controlled) is a German -led program to develop a short-range Air-to-air missile to replace the This is a list of sources of Light, including both natural and artificial sources and both processes and devices. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies Missiles which use infrared seeking are often referred to as "heat-seekers", since infrared (IR) is just below the visible spectrum of light in frequency and is radiated strongly by hot bodies. Many objects such as people, vehicle engines and aircraft generate and retain heat, and as such, are especially visible in the infra-red wavelengths of light compared to objects in the background.
The NATO brevity code for an air-to-air infrared-guided missile launch is "Fox Two"[1]. Multiservice Tactical Brevity Codes are codes used by various military air forces and air defense personnel An air-to-air missile ( AAM) is a guided Missile fired from an Aircraft for the purpose of destroying another aircraft
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Seeker types
The three main materials used in the infrared sensor are lead sulfide (PbS), Indium Antimonide (InSb) and MerCad telluride (HgCdTe). Indium antimonide ( is a Narrow gap Semiconductor material from the III - V group used in Infrared detectors including Thermal HgCdTe or mercury Cadmium Telluride (also cadmium mercury telluride, MCT or CMT) is an Alloy of Older sensors tend to use PbS, newer sensors tend to use InSb or HgCdTe. All perform better when cooled, as they are both more sensitive and able to detect cooler objects.
Early infrared seekers were most effective in detecting infrared radiation with shorter wavelengths, such as the 4. 2 micrometre emissions of the carbon dioxide efflux of a jet engine. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single specific --->A jet engine is a Reaction engine that discharges a fast moving jet of Fluid to Such seekers, which are most sensitive to the 3 to 5 micrometre r which is absorbed least by the atmosphere. Such seekers are called "two-color" systems. Two-color seekers are harder to defeat with countermeasures such as flares and jammers. A countermeasure is a system (usually for a Military application designed to prevent Sensor -based Weapons from acquiring and/or destroying a target A (decoy flare is an aerial infrared countermeasure to counter an Infrared homing ("heat seeking" Surface-to-air missile (SAM or
Scanning patterns and modulation
A missile's resistance to decoys can also be determined by the method in which the space in front of itself is scanned for targets. A decoy is usually a person device or event meant as a distraction to conceal what an individual or a group might be looking for Early missiles used spin scanning while newer seekers use conical scanning which gives them superior decoy discrimination as well as overall increased sensitivity for longer range tracking. There have also been missiles built using so-called "rosette" scanning methods. Very modern heat-seeking missiles utilise imaging infrared (IIR), where the IR/UV sensor is a focal plane array which is able to "see" in infra-red, much like the CCD in a digital camera. A thermographic camera, sometimes called a FLIR (Forward Looking InfraRed or an infrared camera less specifically is a device that forms an image using Infrared A staring array, staring-plane array, focal-plane array (FPA or focal-plane is an image sensing device consisting of an array (typically rectangular of A charge-coupled device ( CCD) is an analog Shift register, that enables the transportation of analog signals (electric charges through successive stages (capacitors This requires much more signal processing but can be much more accurate and harder to fool with decoys. In addition to being more flare-resistant, newer seekers are also less likely to be fooled into locking onto the sun, another common trick for avoiding heat-seeking missiles.
Before imaging infrared sensors there was also the question of sensor modulation; earlier seekers used amplitude modulation (AM) to determine how far off-center the target was and thus how hard the missile had to turn to center it, but this led to increased error as the missile approached the target and the target's image became relatively larger (creating an artificially stronger signal). Amplitude modulation ( AM) is a technique used in electronic communication most commonly for transmitting information via a Radio Carrier wave Switching to frequency modulation (FM) solved this problem, which is better able to discriminate the distance without being further confused by the image size.
Cooling
All-aspect seekers also tend to require cooling to give them the high degree of sensitivity required to lock onto the lower level signals coming from the front and sides of an aircraft. An all-aspect missile is one which is able to track a target no matter which way the target faces relative to the missile Background heat from inside the sensor, or the aerodynamically heated sensor window, can overpower the weak signal entering the sensor from the target. (CCDs in cameras have similar problems; they have much more "noise" at higher temperatures. ) Modern all-aspect missiles like the AIM-9M Sidewinder and FIM-92 Stinger use compressed gas or liquid nitrogen to cool their sensors in order to lock onto the target at longer ranges and all aspects. The AIM-9 Sidewinder is a heat-seeking, short-range Air-to-air missile carried by Fighter aircraft and recently certain gunship helicopters The FIM-92 Stinger is a personal portable Infrared homing Surface-to-air missile developed in the United States and used by all the U In Physics, the Joule–Thomson effect or Joule–Kelvin effect describes the Temperature change of a gas or liquid when it is forced through a Valve Liquid nitrogen (liquid density at the Triple point is 0707 g/mL is the liquid produced industrially in large quantities by Fractional distillation of (The AIM-9J used a peltier thermoelectric cooler). Thermoelectric cooling uses the Peltier effect to create a Heat flux between the junction of two different types of materials
Tracking
Most infrared guided missiles have their seekers mounted on a gimbal. A gimbal is a pivoted support that allows the rotation of an object about a single axis This allows the sensor to be pointed at the target when the missile is not. This is important for two main reasons. One is that before and during launch, the missile can't always be pointed at the target. Rather, the pilot or operator points the seeker at the target using radar, a helmet-mounted sight, an optical sight or possibly by pointing the nose of the aircraft or missile launcher directly at the target. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships Once the seeker sees and recognises the target, it indicates this to the operator who then typically "uncages" the seeker (which is then allowed to follow the target). After this point the seeker remains locked on the target, even if the aircraft or launching platform moves. When the weapon is launched, it may not be able to control the direction it points until the motor fires and it reaches a high enough speed for its fins to control its direction of travel. Until then, the gimballed seeker needs to be able to track the target independently.
Finally, even while it is under positive control and on its way to intercept the target, it probably won't be pointing directly at it; unless the target is moving directly toward or away from the launching platform, the shortest path to intercept the target will not be the path taken while pointing straight at it, since it is moving laterally with respect to the missile's view. The original heat-seeking missiles would simply point towards the target and chase it; this was inefficient. Newer missiles are smarter and use the gimballed seeker head combined with what's known as "proportional guidance" in order to avoid oscillation and to fly an efficient intercept path.
See also
References
- ^ MULTISERVICE AIR-AIR, AIR-SURFACE, SURFACE-AIR BREVITY CODES, Air Land Sea Application (ALSA) Center, 1997, pp. Infrared countermeasures ( IRCM) are devices designed to protect aircraft from Infrared homing ("heat seeking" missiles by confusing the missiles' Infrared Directional Infrared Counter Measures ( DIRCM) is a system produced by Northrop Grumman and BAE Systems to protect Aircraft from Infrared An infra-red search and track ( IRST) system (sometimes known as infra-red sighting and tracking) is a method for detecting and tracking objects which give off 6, <http://www.dtic.mil/doctrine/jel/service_pubs/lbrevity.pdf>. Retrieved on 23 February 2008
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