introduced its OpenPod(TM) IRST pod, which uses a sensor by Leonardo. While IRST systems are most common amongst aircraft, land-based, ship and submarine systems are available. Distributed Aperture Systems The F-35 equipped infrared search and track system AN/AAQ-37 Distributed 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-20 and Shenyang FC-31 shares the similar design concept with their EORD-31 system that provides 360 degree IRST coverage. IRST systems can also be used to detect stealth aircraft, in some cases, outperforming traditional radar. Technology These were fairly simple systems consisting of an infra-red sensor with 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 the B-scopes used 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 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 front and 90 km from rear - the larger value being the consequence of directly observing the engine exhaust, with an even greater increase being possible if the target uses afterburners. The range at which a target can be sufficiently confidently identified to decide on weapon release is significantly inferior to the detection range - manufacturers have claimed it is about 65% of detection range. Tactics With infrared homing or fire-and-forget missiles, the fighter may