irst

IRST commonly refers to Infrared Search and Track, a passive sensor system used on military aircraft, ships, and some ground platforms to detect and track targets by their infrared radiation. Because it is passive, IRST does not emit signals, enabling covert detection and cueing for weapons or other sensors. An IRST system typically consists of a cooled infrared detector array, a scanning mechanism or staring sensor, signal processing hardware, and a user interface. Optional additions include a laser rangefinder for precise distance measurement and data links to share target information with other platforms. The system provides azimuth, elevation, and sometimes range information, allowing the host platform to acquire targets and cue its radar or missiles.

Performance depends on detector sensitivity, background heat, weather, and target heat signature; larger or hotter aircraft are detected at greater ranges. Benefits include covert operation, all-day capability, and resilience against radar jamming. Limitations include reduced performance in poor weather, background clutter, or against very small heat sources, and the need for maintenance of cooling systems in many designs.

Development and deployment of IRST systems have evolved over several decades and they are now integrated on a variety of fighter aircraft and naval vessels, offering a complementary sensing channel to radar. They enable early detection and tracking while minimizing emissions that could reveal the platform’s position.

Alternative meaning: IRST may also stand for Iran Standard Time (UTC+3:30).