Infra-red search and track

An infrared search and track (IRST) system (sometimes known as infrared sighting and tracking) is a method for detecting and tracking objects which give off infrared radiation (see Infrared signature) such as jet aircraft and helicopters.

IRST is a generalized case of forward looking infrared (FLIR), i.e. from forward-looking to all-round situation awareness. Such systems are passive (thermographic camera), meaning they do not give out any radiation of their own, unlike radar. This gives them the advantage that they are difficult to detect.

However, because the atmosphere attenuates infrared to some extent (although not as much as visible light) and because adverse weather can attenuate it also (again, not as badly as visible systems), the range compared to a radar is limited. Within range, angular resolution is better than radar due to the shorter wavelength.

The first use of an IRST system appears to be the F-101 Voodoo, F-102 Delta Dagger and F-106 Delta Dart interceptors. The F-106 had an early IRST mounting replaced in 1963 with a production retractable mount. The IRST was also incorporated into the Vought F-8 Crusader (F-8E variant) which allowed passive tracking of heat emissions and was similar to the later Texas Instruments AAA-4 installed on early F-4 Phantoms.

The F-4 Phantom had a Texas Instruments AAA-4 infrared seeker under the nose of early production aircraft F-4B's and F-4C's and not installed on later F-4-D's due to limited capabilities, but retained the bulge and indeed some F-4D's had the IRST receiver retrofitted in a modified form.

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