Re: Chlorophyll absorption

["Lee Tarpley" <tarpley@xxxxxxxxxxxxxx>]

> From: Willem-Jan Markerink <w.j.markerink@xxxxx>
> To: infrared@xxxxx
> Subject: Chlorophyll absorption
> A nice article, in addition to the IR-reflection of chlorophyll:

(W-J had forwarded a discussion that had appeared in sci.optics and that
included information about the absorbance spectra of chlorophyll and other
plant pigments)

Just for clarification, others have shown that the reflectance by leaves of
very near infrared radiation is not reflectance by chlorophyll, but is
probably due to internal cellular structure (perhaps refractive index
discontinuities associated with the cell walls). The white portion of
variegated leaves also has high reflectance of the VNIR! Also, in remote
sensing, folks sometimes use VNIR reflectance as part of an index for
health of the foliage - the less healthy, the less reflectance. The amount
of VNIR reflectance per unit leaf area often does not change in a way that
is consistent with a decline in chlorophyll content in unhealthy leaves. It
is rather the loss of leaves (or possibly drooping leaves) or less plant
growth that leads to less VNIR reflectance per unit of ground area in the
remote image of unhealthy foliage.

Lee Tarpley

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