Re: general questions about IR

[Ben Kreunen <ben@xxxxxxxxxxxxxxxxxxxxxxx>]

>I'm not suggesting that materials that absorb IR are hotter at the time
>the picture is taken, or that the film is recording temperature. I know
>that IR film does not record temperature. I am asking that if a
>material absorbs IR, as shown by the film as being "not red" in EIR or
>black in HIE, that it will behave in such a way as to be hotter in
>temperature as compared to materials that reflect IR given that each is
>exposed to the same amount if IR light. From experience, I can tell you
>that materials like brick, gravel, asphalt, etc. are much hotter to the
>touch than any living plant material in full sun. Even a thin sheet of
>metal the same mass as a leaf will be hotter to the touch in the same
>light.

Think of black clothing that appears light in IR pics because of the 
dyes.  It'll still make you hot in the sun.

There are other properties associated with rocks as well that determine IR 
reflectance. The third pic on this page 
<http://www.bigbenpublishing.com.au/victoria/grampians/frederick.html> for 
example shows a thin line of scorched sandstone after a bushfire, where the 
heat of the fire removed most of the water in the sandstone. Mineral 
composition and crystal structure may also play a role in what wavelengths 
are reflected just as the cellular structure of leaves (including conifers) 
will affect reflectance.  In any case this is not related to the absorption 
of thermal energy.

Cheers

Ben

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http://www.bigbenpublishing.com.au/
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