[leoedin]

What you're describing is 2 or 3 sensors - effectively 2 or 3 pixels. Enough to discriminate when an aircraft launches a flare, but not really "imaging" in the modern sense.

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.