Infrared search and track

"IRST" redirects here. For the time zone in Iran, seeIran Standard Time.

An IRST sensor on aSukhoi Su-35

AnInfrared Search and Track(IRST) system (sometimes known asinfrared sighting and tracking) is a method for detecting and tracking objects which give offinfraredradiation,such as theinfrared signaturesofjet aircraftandhelicopters.

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

However, because the atmosphere attenuates infrared to some extent (although not as much asvisible light) and because adverse weather can attenuate it also (again, not as badly as visible systems), their range compared to a radar is limited. Within range, an IRST'sangular resolutionis better than radar due to the shorterwavelength.

History

Early systems

AnF-8E CrusaderofVMF(AW)-235atDa Nang,in April 1966 showing the IRST in front of the canopy.

The first uses of an IRST system appeared in theF-101 Voodoo,F-102 Delta DaggerandF-106 Delta Dartinterceptors.The F-106 had an early IRST mounting replaced in 1963 with a production retractable mount.The IRST was also incorporated into theF-8 Crusader(F-8E variant) allowing passive tracking of heat emissions and was similar to the laterTexas InstrumentsAN/AAA-4installed on earlyF-4 Phantoms.

AN/AAA-4 IRST under nose of F-4 Phantom

The F-4 Phantom had a Texas Instruments AAA-4 infrared seekerunder the nose of early production aircraft F-4Bs and F-4Cs. It was not not installed on later F-4Ds due to limited capabilities,but retained the bulge and indeed some F-4Ds had the IRST receiver retrofitted in a modified form.

The F-4E eliminated the AAA-4 IRST bulge and received an internal gun mount which took up the area under the nose.The F-4J which had apulse-Doppler radaralso eliminated the AAA-4 IRST receiver and bulge under the nose.

The first use of IRST in an Eurasian country was theMikoyan-Gurevich MiG-23,which used the (TP-23ML) IRST; later versions used the (26SH1) IRST.TheMikoyan-Gurevich MiG-25PD was also equipped with a small IRST under the nose.

The SwedishSaab J-35F2 Draken(1965) also used an IRST, aHughes Aircraft CompanyN71.

Later systems

IRST systems re-appeared on more modern designs starting in the 1980s with the introduction of 2-D sensors, which cuedboth horizontal and vertical angle. Sensitivities were also greatly improved, leading to better resolution and range. In more recent years, new systems have entered the market. In 2015, Northrop Grumman introduced its OpenPod IRST pod,which uses a sensor byLeonardo.The United States Air Force is currently incorporating IRST systems for its fighter aircraft fleet, including the F-15, F-16, and F-22.

Optronique secteur frontal(IRST) of theDassault Rafale,below the cockpit and to the side of the refueling boom. On the left, the main IR sensor (100 km range), on the right a TV/IR identification sensor withlaser rangefinder(40 km range)

Eurofighter Typhoonwith PIRATE IRST

While IRST systems are most common amongst aircraft, land-based, ship and submarine systems are available.

Distributed Aperture Systems

TheF-35is equipped with infrared search and track systemAN/AAQ-37Distributed Aperture System (DAS), which consists of six IR sensors around the aircraft for full spherical coverage, providing day/night imaging and acting as an IRST and missile approach warning system.

Chengdu J-20andShenyang FC-31is assumed to share the similar design concept with their system.IRST systems can also be used to detect stealth aircraft, in some cases, outperforming traditional radar.

Technology

These were fairly simple systems consisting of aninfra-red sensorwith a horizontally rotating shutter in front of it. The shutter was slaved to a display under the main interception radar display in the cockpit. Any IR light falling on the sensor would generate a "pip" on the display, in a fashion similar to theB-scopesused on early radars.

The display was primarily intended to allow the radar operator to manually turn the radar to the approximate angle of the target, in an era when radar systems had to be "locked on" by hand. The system was considered to be of limited utility, and with the introduction of more automated radars they disappeared from fighter designs for some time.

Performance

Detection range varies with external factors such as

• clouds
• altitude
• air temperature
• target's attitude
• target's speed

The higher the altitude, the less dense the atmosphere and the less infrared radiation it absorbs - especially at longer wavelengths. The effect of reduction in friction between air and aircraft does not compensate for the better transmission of infrared radiation. Therefore, infrared detection ranges are longer at high altitudes.

At high altitudes, temperatures range from −30 to −50 °C - which provide better contrast between aircraft temperature and background temperature.

The Eurofighter Typhoon's PIRATE IRST can detect subsonic fighters from 50 km from the front and 90 km from the rear- the larger value being the consequence of directly observing the engine exhaust, with an even greater increase being possible if the target usesafterburners.

The range at which a target can be identified with sufficient confidence to decide on weapon release is significantly inferior to the detection range - manufacturers have claimed it is about 65% of the detection range.

Tactics

MiG-29 nose showing radome and S-31E2 KOLS IRST

Withinfrared homingorfire-and-forgetmissiles, the fighter may be able to fire upon the target without having to turn on its radar sets on at all. Otherwise, the fighter can turn the radar on and achieve a lock immediately before firing if desired. The fighter could also close to withincannonrange 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 ordinaryforward looking infraredsystem, an IRST system will actually scan the space around the aircraft similarly to the way in which mechanically (or even electronically) steered radars work. The exception to the scanning technique is the F-35's DAS, which stares in all directions simultaneously, and automatically detects and declares aircraft and missiles in all directions, without a limit to the number of targets simultaneously tracked.

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 aircraft).

IRST systems can incorporatelaser rangefindersin order to provide fullfire-controlsolutions for cannon fire or launching missiles (Optronique Secteur Frontal). The combination of an atmospheric propagation model, the apparent surface of the target, and target motion analysis (TMA) IRST can calculate the range.

List of modern IRST systems

The best known modern IRST systems are:

• France
  • Classe Orizzonte frigate(SafranVampir MB)
  • ROKSDokdoamphibious assault ship (Safran Vampir MB)
  • Sejong the Great-class destroyer(Safran Vampir NG)
  • Anzac-class frigate(Safran Vampir NG)
  • Canberra-class landing helicopter dock(Safran Vampir NG)
  • Hobart-class destroyer(Safran Vampir NG)
  • Cassard-class frigate(Safran EOMS-NG)
  • Floréal-classfrigate(Safran EOMS-NG)
  • Horizon-class frigate(Safran EOMS-NG)
  • Baynunah-class corvette(Safran EOMS-NG)
  • Gowind-class OPV for Argentina(Safran EOMS-NG)
  • Aircraft carrierCharles de Gaulle(ThalesARTEMIS)
  • FREMM(Thales ARTEMIS)
  • Dassault Rafale(Safran/ThalesOptronique secteur frontalOSF)
• Italy
  • Aircraft carrierCavour(LeonardoSASS)
  • FREMM(Leonardo SASS)
  • Doha-class corvette(Leonardo SASS)
  • Musherib-class offshore patrol vessel(Leonardo SASS)
  • Saab JAS 39 Gripen E/F(Leonardo Skyward-G)
  • LHDTrieste(Leonardo DSS-IRST)
• Italy/Spain/United Kingdom
  • Eurofighter Typhoon(EuroFIRST PIRATE)
• Japan
  • Mitsubishi F-15J
• Netherlands
  • Halifax-class frigate(Thales NederlandSirius)
  • De Zeven Provinciën-class frigate(Thales Nederland Sirius)
  • Sachsen-class frigate(Thales Nederland Sirius)
• Russia
  • Su-27/30/33/35/37 Flanker(OEPS-27/30; OLS-35)
  • Mikoyan MiG-31(8TK)
  • MiG-29/35(OEPS-29/OLS-13SM-1)
  • Sukhoi Su-57(101KS-V)
• South Korea
  • ROKSMaradoamphibious assault ship (HanwhaSAQ-600K)
  • Daegu-class frigate(Hanwha SAQ-600K)
  • KAI KF-21 Boramae
• Spain
  • F110-class frigate(Indra/TecnobitIRST i110)
• Sweden
  • JAS-39E/F Gripen NG(Skyward-G)
• Turkey
  • Barbaros-class frigate(AselsanPIRI)
  • TCGAnadolu(Aselsan PIRI)
  • Istanbul-class frigate(Aselsan PIRI)
  • TAI TF Kaan
• United States
  • Vought F-8 Crusader
  • Grumman F-14D Tomcat(AN/AAS-42 IRST)
  • McDonnell Douglas F-15C Eagle(Lockheed MartinAN/ASG-34 IRST21 in Legion Pod)
  • Boeing F-15K/SG/SA/QA/IAStrike/Advanced Eagle (AN/AAS-42 “Tiger Eyes” )
  • Boeing F-15EX Eagle II(AN/ASG-34 in Legion Pod)
  • Lockheed Martin F-16C/D/V(AN/ASG-34 in Legion Pod)
  • Lockheed Martin F-16E/F Block 60/62(AN/AAQ-32 IFTS)
  • Boeing F/A-18E/F Super Hornet Block III(AN/ASG-34)
  • Lockheed Martin F-22 Raptor(AIRST)
  • Lockheed Martin F-35 Lightning II(AN/AAQ-40 Electro-Optical Targeting System,AN/AAQ-37 Electro-optical Distributed Aperture System)
  • Arleigh Burke-class guided missile destroyer(Mark 46 Mod 1 on Flight I/II/IIA, Mark 20 Mod 1 on Flight III)
  • Phalanx CIWS Block 1B

Fighter aircraft carry the IRST systems for use instead of radar when the situation warrants it, such as when shadowing other aircraft, under the control ofairborne early warning and control(AWACS) aircraft, or executing aground-controlled interception(GCI), where an external radar is used to help vector the fighter to a target and the IRST is used to pick up and track the target once the fighter is in range.

See also

• Electro-optical targeting system
• AN/AAQ-37 Electro-optical Distributed Aperture System

References

Bibliography

• Mahulikar, S.P.; Sonawane, H.R.; Rao, G.A. (2007), "Infrared signature studies of aerospace vehicles",Progress in Aerospace Sciences,43(7-8): 218–245
• Eden, Paul, ed. (2004),The Encyclopedia of Modern Military Aircraft,London: Amber Books Ltd,ISBN1-904687-84-9
• Kinzey, Bert (1983),F-106 Delta Dart, in Detail & Scale,Fallbrook, CA: Aero Publishers,ISBN0-8168-5027-5.
• Sweetman, Bill; Bonds, Ray (1987),The Great Book of Modern Warplanes,New York, New York: Crown Publishers,ISBN0-517-63367-1

External links

• Fraunhofer Institut IAF annual report 2006German and English.