Thread by @heatloss1986

If you ever hear me talking about FIM-92 Stinger as if it's the best thing since sliced bread, that's cause it kinda is.
A short thread on the Stinger-Passive Optical Seeker Technique(POST) seeker.

The POST seeker is a pretty exceptional piece of kit. It provides advanced countermeasure rejection through two different methods that I'll walk through.

Let's start with the easy one: dual color. A dual-color IR/UV seeker looks for a positive infrared signal and a negative UV signal because an aircraft blocks out UV.
Stinger POST used Indium Antimonide for IR and Cadmium Sulfide for UV.

On its own, this is moderately powerful, but it gets far more effective when combined with the other technique: rosette scanning. This is a system that operates with a very narrow field of view and relies on a complex scan pattern to cover a larger FoV and detect the target.

Rosette scanners work using two counterrotating prisms to create this complex pattern. TFOV stands for True Field of View, and IFOV for Instantaneous Field of View. The IFOV needs to be small to increase the resolution of this scan.

Now here's what it looks like with a target and flares. The red dot with a white circle around it (sorry this image sucks) is a target, and the four blue dots are flares. As you can see, the target is larger and will show up during more passes of the scan pattern.

Rosette scanning is referred to as a form of "pseudo-imaging", and it allows for some basic counter-countermeasures through signal processing, but it isn't perfect on its own.

But wait, remember that second seeker color? The target blocks UV, but flares do not! In the second color, all of the rosette scan would provide a positive return, including the areas with flare groups, except for the target!

This allows the processor to rule out the sectors with flares as not-the-target. The biggest downside to rosette scanning is the processing penalty it incurs, but this was made possible by the digitization of the Stinger.

for the stuff about Stinger. I'm honestly quite surprised that this is completely public info, which is the only reason I considered posting about this.apps.dtic.mil/sti/pdfs/ADA45…
history.redstone.army.mil/miss-stingerav…
odin.tradoc.army.mil/WEG/Asset/FIM-…