Remote thermal detection

On Monday, October 3, 2016 at 4:04:39 AM UTC+13, Jonathan St. Cloud wrote:
A FLIR unit might offer a visual indication from much larger distance?

A few moons ago, I got chatting to a guy selling FLIR imaging systems at a trade show. I asked him about the problem of trying to see thermals, so we set an imager up to look at the hot air rising from a nearby vent and saw nothing (as he expected).
There's no problem seeing warm solid objects, since they consist of a lot of closely-packed warm emitters - high spatial density - but warm gas is so much more diffuse that any infrared 'brightness' just fades into the background, like a small amount of dye in a large volume of liquid. To do effective background subtraction, you need to know what the background is to begin with and on a typical thermal day this is the average temperature of the air which has high spatial variability.
I think birds can see all those rising insects, which makes the birds the best thermal indicators, if they can be bothered to fly where we want them to.

DH
TX