I agree with Brian and don’t think that claim as far fetched at all.
I did a test using a standard gallon milk jug full of 105° water when I left the house and set it out on the road and drove away from it as far as I could to test my ability to detect the object using two thermal devices I had with me at the time. My FLIR vue pro 19 mm 640, and my IRD Mark two 35 mm 640.
The flir is mounted inside a go light on the roof of my truck and it’s hooked up to my laptop computer sitting on my dashboard and I use it to navigate with. I was a astounded to discover that I could detect the milk jug to just over 800 yards.
Here is a YouTube video and the actual digital video file created by the FLIR Vue which gives a better detailed image then when I was seeing on my computer display.
For what it’s worth, I could detect the jug with the IRD out to 1200 yards which is as far away as I could drive on that particular test range.
New folder - Google Drive
You may have to download the Google Drive file for it to play but it is a little bit of better image than the YouTube video.
I have been told that detection consist of 3.5 pixels. My FLIR with 19 mm lens has a field of view of 32°. At 400 yards I should be down to one pixel yet, I was able to detect the jug at twice that distance as seen in this video.
The intersection in the road that you can see when I pass it is approximately 550 yards away from that jug.