Re: Wood effect

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On 22 Oct 99 at 20:44, Carl Schofield wrote:

> ----------
> >From: Jesko-Henning Tanke <jesko-henning@xxxxxxxxxxx>
> >Subject: Re: Wood effect
> 
> The effect is caused by the structure of
> > the chlorophyll containing leafs, which absorb most radiation below
> > infrared. Only green gets (mostly) emitted after beeing reflected in the
> > parenchym layer of the leaf. Wavelengths above 680nm are reflected there
> > with no absorbtion at all thus producing the nice light spots on the IR
> > film.
> 
> If chlorophyll absorption of visible light is involved in this effect then
> why do red and gold autumn leaves still produce that nice white glow in IR
> images?

The top layer of leafs is transparent to IR, regardless of its visual 
color. The reflection of IR itself takes place on a deeper level, 
where these parenchym (sp?) cells resides. Forgot whether chlorophyl 
is the visual top layer or not.
Interesting detail: the physical properties of these parenchym cells, 
responsible for the reflection, is the same for snow: cells of air 
trapped between other material. Walter Clark described this in his 
book; a copy of that text is on my homepage:

http://www.a1.nl/phomepag/markerink/mainpage.htm

(page name probably ir_snow.htm)  

--                 
Bye,

Willem-Jan Markerink


      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]
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