From: Ian Goddard (Ian@Goddard.net)
Date: Sat Sep 11 1999 - 20:05:21 MDT
At 02:48 PM 9/11/99 -0700, Robert J. Bradbury wrote:
>I think you need to study some physics about
>light, heat and reflections.
>
>The infrared enegy coming off of an object sitting
>in the sun can be *alot* greater than the infrared
>energy it receives. The object absorbs the visible
>light energy and re-emits it in the infrared.
>Why do you think black tar or sand gets *hot*?
>The amount of IR emitted by the object is going
>to be proportional to its absorbance of other
>frequencies.
>
> ....
IAN: Reflected visible light from the sun
is NOT infrared radiation, yet you errantly
think that because a body radiates IR an FLIR
can pick up the visible light of the reflection,
it does not. The visible radiation reflecting
off a body is not going to be much hotter than
the IR radiaton coming off the body, which is
why the FLIR did not pick up reflections off
the body of water * from any angle * Hello!
>I would leave the determination of reflections vs.
>gun muzzle flashes to people who are trained to
>interpret FLIR images.
IAN: Hubba hubba. Fine, then listen to Doctor
Edward Allard, who not only worked much of his
life for the military in IR imaging but also
holds patents in IR-imaging technology:
"...materials which reflect sunlight and thus
seem bright in the visual spectrum will often
appear indistinct, or even dark, to a thermal
imager; the very reflective properties that make
them bright to the eye make them appear cool,
and thus dark, to FLIR systems. Interpretation
of thermal images requires a knowledge of the
reflective properties of both natural and
man-made objects."
http://www.indirect.com/www/dhardy/allard.html
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