OVERVIEW: Infrared Search and Track (IRST) is a passive sensor system that detects and tracks objects based on their infrared (heat) emissions. Unlike radar, IRST does not emit signals, making it stealthy and resistant to detection or jamming. IRST is commonly used in air-to-air and surface-based applications to provide long-range surveillance, target detection, and tracking capabilities.

DETAILS: IRST systems utilize infrared sensors, often cooled mid-wave (MWIR: 3–5 µm) or long-wave (LWIR: 8–12 µm), to passively scan the environment for heat sources such as aircraft, missiles, or ground vehicles. Advanced IRST systems use imaging arrays and real-time processing to classify targets and provide angle-of-arrival data, often integrating with fire control systems.
On fighter aircraft, IRST provides an advantage in beyond-visual-range engagements without alerting the enemy through radar emissions. On naval platforms, IRST contributes to anti-air and anti-surface surveillance. The system’s passive nature makes it effective in environments where emissions control (EMCON) is critical.
IRST performance depends on factors such as sensor sensitivity, atmospheric conditions, and target contrast. Modern IRST systems may also integrate laser rangefinders or work in conjunction with radar and electronic warfare systems to enhance tracking and targeting capabilities.

ROLE SUMMARY:
Category: Passive Infrared Imaging Target Detection
Primary Use: Long-range detection, tracking, and identification of aerial and surface targets
Function: Thermal imaging and passive scanning for situational awareness and fire control cueing
Strong Against: Stealth aircraft, non-emitting targets, and targets in radar-denied environments
Weak Against: Low-IR-signature objects, atmospheric obscurants (clouds, rain), and clutter
Platform: Fighter aircraft, maritime patrol aircraft, naval vessels
Integration: Works with radar, weapons systems, and electronic warfare suites

-Second-generation IRST: Often utilizing focal plane arrays, to provide detailed thermal images of targets. This allows improved target recognition and engagement in all weather and low-visibility conditions. Offering stealthy detection of airborne and maritime threats.

See Specific information under [Sensors/EW] and [Properties] sections.

SOURCE:
Jane’s Airborne Sensors
https://en.wikipedia.org/wiki/Infrared_search_and_track