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 Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ...infrared radiation such as Jet aircraft are aircraft with jet engines. ...jet aircraft and A helicopter is an aircraft which is lifted and propelled by one or more large horizontal rotors (propellers). ...helicopters. Such systems are passive, meaning they do not give out any radiation of their own, unlike M*A*S*H, see Corporal Walter (Radar) OReilly. ...radar. This gives them the advantage that they are undetectable. However, because the atmosphere does attenuate infra_red light to some extent (although not as much as visible light) and because weather can adversely affect it also (again, not as badly as purely optical systems), the range compared to a radar is limited.

Some modern aircraft, typically fighter or interceptors like the The term Russian can refer to: The Russian language Someone from Russia or with a Russian ethnic identity, see Russians Something of or pertaining to Russia Wiktionary information For more information: Russian This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same...Russian The Sukhoi Su_27 (NATO reporting name Flanker) is a Russian fighter aircraft designed by the Sukhoi Design Bureau (SDB). ...Su_27 Flanker or American, when used as an adjective, can mean of the United States of America or of or relating to the Americas; when used as a noun, United States citizen, residing in the Americas, or less frequently American English. Immigrants to the United States are usually called first_generation Americans, regardless...American Sailors prepare an F_14 Tomcat for flight on the aircraft carrier USS Abraham Lincoln, in support of Operation Iraqi Freedom (2003). ...F_14 Tomcat, carry IRST systems for use in lieu of their radars when the situation warrants it, such as when shadowing other aircraft or under the control of US Air Force E_3 Sentry AWACS aircraft is prepared for flight in November 1997 Cockpit of RAF E_3 Sentry undergoing upgrades Airborne Warning and Control System (AWACS) is a radar_based electronic system designed to carry out airborne surveillance, and C3 (command, control and communications) functions for both...AWACS or GCI, where an external radar is being used to help vector them onto a target and the IRST is used to pick up and track the target once they are in range. With infra-red homing or Fire and forget is the military term for a type of missile which does not require further guidance after launch such as illumination of the target, and can hit its target without the launcher being in line of sight of the target. ...fire_and_forget missiles, the aircraft may be able to fire upon the targets without having to turn their radar sets on at all. Otherwise, they can turn the radar on and achieve a lock immediately before firing if desired. They could also close to within A small cast_iron cannon on a carriage A cannon is a modern day rifled machine gun with a calibre of 20 mm or more (see autocannon). ...cannon range and engage that way. Whether or not they use their radar, the IRST system can still allow them to launch a surprise attack.

An IRST system may also have a regular magnified optical sight slaved to it, to help the IRST_equipped aircraft identify the target at long range. As opposed to an ordinary [[forward_looking infra[red]] system, an IRST system will actually scan the space around the aircraft similarly to the way in which mechanically (or even electronically) steered radars work. When they find one or more potential targets they will alert the pilot(s) and display the location of each target relative to the aircraft on a screen, much like a radar. Again similarly to the way a radar works, the operator can tell the IRST to track a particular target of interest, once it has been identified, or scan in a particular direction if a target is believed to be there (for example, because of an advisory from AWACS or another aircrraft).

Note that like infra_red homing seekers, an IRST is more likely to detect a target with its engine exhaust pointed towards the detector than away from it. This means that many jet aircrafts will be detected at longer ranges if they are flying away from the IRST_equipped aircraft rather than towards it. However, most IRST systems are sensitive enough to detect the heat of a jet from head_on as well, either infra_red energy generated from the hot air coming out of the engines, from air friction heating the airframe, or both.

Infra_red search and track systems often incorporate laser range-finders in order to provide full A fire-control system is a computer, often mechanical, which is designed to assist a weapon system in hitting its target. ...fire control solutions for cannon fire or launching missiles. Without knowing the range (which could be estimated using the infra_red signature of the target or other factors, but would be very inaccurate), the IRST can only provide direction and thus not enough information for aiming weapons.

Infra_red search and track and forward_looking infra_red are sometimes used interchangeably but a system which has automated searching and tracking functions, rather than being fixed looking forward or manually steerable, is more specifically known as IRST whereas an FLIR is often little more than an infra_red camera hooked up to a monitor. IRST is more often used against aircraft, but can find and track ground targets, whereas FLIRs are more often found on ground attack aircraft.

See also: Forward-looking infra-red