Peter wrote:
> Next you will tell me colored people emit differently from whites

Well, actually, yes.  Think about it.  If they didn't you couldn't
distinguish them by color.  It may be that there is little distinction in
the IR range, but there could be since there certainly is in the visible
range.

> It's blackbody radiation, and everything emits it and absorbs it.

No, only truly black bodies do.  Everything else emits and absorbes less.
That's why air, being transparent to IR, emits virtually no IR itself.  It
can, however, warm or cool things it contacts and cause them to emit a
different IR signature.  Pockets of hotter or colder air will also refract
light, so such pockets moving in front of a IR sensor can make it look like
the IR coming from the objects behind the pockets is changing.  This is the
same effect as when you see "shimmering heat" off the highway in front of
you in the summer.  You're not seeing the hot air, but you are seeing the
refraction effects of the thermal gradients in the air.


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