International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
Physical-based studies have shown that shortwave infrared
(SWIR) (1400-2500 nm) is strongly influenced by the water
in plant tissue (Gausman, 1984). In particular, the
wavelengths at 1530 and 1720 nm seem to be most
appropriate for assessing vegetation water (Fourty & Baret,
1998). The water fills out the cavities, forming a more liquid
environment inside the leaf. With this, occurs a decreasing of
the differences of the refraction index between the air and the
hydrated cell wall, which increases its transmittance and
decreases the reflectance (Moreira, 2001). Therefore the here
shown results express, inter alia, mainly the differences in
plant water content for the four pastures. This leads to the
assumption that vegetal water content, which is linked to
productivity, is responsible for the second highest correlation
coefficient between reflectance spectra and SOC.
4. CONCLUSIONS
Due to the urge of reliable, fast and inexpensive SOC
estimation in accordance with environmental politics as the
Kyoto Protocol, the study evaluated the potential of orbital
remote sensing for this purpose.
It was observed a good correlation (r = 0,97) between SOC
and LAI. Several studies point out, that the LAI can be
calculated in satellite images by the NDVI (e.g. Friedl, 1997).
Under this assumption, the good correlation between SOC
and LAI leads to the promising approach to estimate current
and potential SOC by remotely sensed LAI determination.
Furthermore was identified an also good correlation between
SOC and some spectra of pasture reflectance. A regression
analysis showed particularly good correlations in the red (r =
0,96) and shortwave infrared 1 (r = 0,95) spectra. The red
spectrum refers mainly to photosynthesis activity and the
SWIR I spectrum to waterleaf content of the pastures. The
good correlations in these two spectra with SOC lead to the
conclusion, that photosynthesis activity and waterleaf
content, that are detectable by orbital remote sensing, can be
linked to SOC. It is of interest to investigate these three
shown correlations of LAI, red and SWIR I spectrum in
relation to SOC in time and space under similar and different
circumstances to verify its validation and study the
possibilities of its applicability for different pasture or other
land use settings.
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ACKNOWLEDGEMENTS
The authors thank for the research support, provided by
Conselho Nacional de Desenvolvimento Científico, Brazil
(CNPq) with Grant No. 133344-2000-2 and financial support
by the Institut de Recherche pour le Développement (IRD),
France.
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