The USAF has had them since 1956: https://en.wikipedia.org/wiki/AIM-4_Falcon
I'd imagine small computers have made them more effective in the last decade or two, but that probably applies to detection and countermeasures in the victim aircraft as well.
Pretty simple and probably quite effective if true.
https://en.wikipedia.org/wiki/Flare_(countermeasure)
> The newest generation of the FIM-92 Stinger uses a dual IR and UV seeker head, which allows for a redundant tracking solution, effectively negating the effectiveness of modern decoy flares (according to the U.S. Department of Defense).
This stuff is a constant back-and-forth of tech improvements.
I'm pretty sure I could buy everything I'd need to build a thermal imaging tracker for a few hundred dollars. So perhaps not surprising that Iran did the same.
>>Flares, the standard IR countermeasure, are less effective against imaging IR seekers that can distinguish an aircraft shape from point-source decoys.
https://en.wikipedia.org/wiki/9K38_Igla
> The 9K310 Igla-1 system and its 9M313 missile were accepted into service in the Soviet Army on 11 March 1981. The main differences from the Strela-3 included an optional Identification Friend or Foe system to prevent firing on friendly aircraft, an automatic lead and super elevation to simplify shooting and reduce minimum firing range, a slightly larger rocket, reduced drag and better guidance system extend maximum range and improve performance against fast and maneuverable targets, an improved lethality on target achieved by a combination of delayed impact fuzing, terminal maneuver to hit the fuselage rather than jet nozzle, an additional charge to set off the remaining rocket fuel (if any) on impact, an improved resistance to infrared countermeasures (both decoy flares and ALQ-144 series jamming emitters), and slightly improved seeker sensitivity.
> The seeker has two detectors – a cooled MWIR InSb detector for detection of the target and uncooled PbS SWIR detector for detection of IR decoys (flares). The built-in logic determines whether the detected object is a target or a decoy. The latest version (Igla-S) is reported to have additional detectors around the main seeker to provide further resistance against pulsed IRCM devices commonly used on helicopters.
> Since 2014 the Igla is being replaced in Russian service by the new 9K333 Verba (Willow) MANPADS.[4] The Verba's primary feature is its multispectral optical seeker, using three sensors as opposed to the Igla-S' two. Cross-checking sensors against one another better discriminates between relevant targets and decoys, and decreases the chance of disruption from countermeasures, including lasers that attempt to blind missiles.
No one's likely to have been surprised by this capability. It's 80s tech.
Early heat seeking missiles would use a single IR sensor with mechanical scanning.
Thermal imaging and machine vision, of the kind you can now do cheaply, isn't 80s tech. It's probably late-90s tech for advanced western states. And now it's starting to be ubiquitous cheap tech too. You can buy a thermal imaging camera with 20k pixels for a few hundred dollars now. Combine that with some image processing and you've got a very robust target detection pipeline.