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Spectrally continuous hyperspectral data can detect subtle
absorption features in foliar spectra. Vegetation reflectances
from hyperspectral remote sensing contain information on the
vegetation chlorophyll absorption bands in the visible regions,
and the effects of plant water absorption in the middle infrared
region. Hyperspectral measurements in very narrow bands are
helpful to study the correlations of these minor absorption
features with biochemical parameters. We can identify unique
absorption features and distinguish vegetation types and extract
biophysical information. Information on vegetation structure
and biochemistry can be estimated from hyperspectral data
and is important for studying nutrient cycling, productivity,
and vegetation stress and for ecosystem modeling.
Hyperspectral data of the Compact Airborne Spectrographic
Imager (CASI) has been applied for mapping biophysical parameters
(Chen et al., 1999). Using measured canopy structural parameters
(LAI, clumping index etc.,), background reflectance, and leaf
spectra as inputs, canopy hyperspectral reflectance spectra
were simulated using the hyperspectral geometrical optical
model (4-scale) and compared well with CASI data over black
spruce forests. The effects of the leaf area index and solar
zenith angle on the canopy reflectance were simulated using
the model, and the complex interaction between radiation and
the canopy at various wavelengths is considered through the
use of the multiple scatting factor spectrum simulated by
the model. A look up table approach is being developed for
inversion from a canopy reflectance spectrum to a leaf reflectance
spectrum for retrieving leaf chlorophyll and other properties
using the leaf-level inversion model (Zhang et al., 2005).
The inversion algorithm is being considered as one of the
candidates for operational use for the Canadian Hyperspectral
Environmental and Resources Observer (HERO), a new mission
under consideration by Canadian Space Agency. Preliminary
investigation shows that this approach can be successfully
applied to analyzing CASI images (Chen et al., 2005).
References
Chen, J. M., Y. Zhang, A. Simic, J. R. Miller, T. Noland.
2005. "Hyperspectral algorithms for forestry applications".
Workshop on Resource and Environmental Hyperspectral Monitoring
Products. Natural Resources Canada, Victoria, January 24-26,
2005. Plenary presentation.
Chen, J.M., Leblanc, S.G., Miller, J.R., J. Freemantle, S.
E., Loechel, C. L., Walthall, K. A., Innanen, H., White, P.
1999. Compact Airborne Spectrographic Imager (CASI) used for
Mapping Biophysical Parameters of Boreal Forests. Journal
of Geophysical Research-Atmosphere, Vol.104, No. D22, pp.
27,945-27,948.
Zhang Yongqin., Jing M. Chen, John Miller, and Thomas Noland,
2005, A canopy-leaf inversion technique for retrieving leaf
chlorophyll content from hyperspectral imagery. (in preparation)
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