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- For a damaged foliage
a) At 680nm, the reflectance is higher than that of
the healty one and increases with the withering.
b) with respect to the yellow band, the relative
reflectance Rogo increases with the damages ; <n summer, when this
factor is higher than one, it is an assured signal of necrosis.
c) in the near infrared, R is no more a constant, but
increases between 800nm and 900nm ; the worse is the sanitary state,
the higher is the slope dR/dA.
Those characteristics, emphasized on the laboratory registered
spectrum can be found, but slightly attenuated, on the spectrum
registered in situ (see figures).
Remark : by measuring reflected energies in the laboratory, we
have noticed that the reflectance of a plant in the near infrared
part of the spectrum decreases meanwhile the damaged surface increase
The absolute value of R on trees 4{n s{tu would certainly give a
significant extra parameter.
These results show that the relative spectral distributions of
reflected energy are very significant of the sanitary State of observec
plants.
It appears that it is necessary to go on with this study and its
application to the teledetection method by improving the four following
points
1, To reduce both the storage and calculation times of data in
order to register a lot a spectra on a greater number of plants.
2. To extend the spectrum towards the infrared to seek for other
eventual necrosis significant parameters for different species.
3. To build a spectroradiometer which can be used on board of an
helicopter.
4. To do in 4itu absolute energy measurements with references
given by pyrheliometer and pyranometer.
Since july 1976, we are working jointly with :
- Institut für Physikalische Weltraumforschung
(MM. H.J. BOEHNEL et W. FISCHER)
- Abteilung Luftbildmessung U.- Interpretation des Institutes
für Forsteinrichtung der Universität Freiburg.
(Pr, G. HILDEBRANDT).