TY - JOUR
T1 - Spectroscopy of canopy chemicals in humid tropical forests
AU - Asner, Gregory P.
AU - Martin, Roberta E.
AU - Knapp, David E.
AU - Tupayachi, Raul
AU - Anderson, Christopher
AU - Carranza, Loreli
AU - Martinez, Paola
AU - Houcheime, Mona
AU - Sinca, Felipe
AU - Weiss, Parker
N1 - Funding Information:
We thank G. Powell, A. Lugo, A. Bin Suhaili, A. Townsend, C. Cleveland, J. Wright, N. O'Connor, and the many assistants who helped with logistics, field work and laboratory analyses. We thank W. Verhoef for providing the 4SAIL2 canopy model. The Spectranomics Project ( http://spectranomics.ciw.edu ) is supported by the John D. and Catherine T. MacArthur Foundation and the Gordon and Berry Moore Foundation.
PY - 2011/12/15
Y1 - 2011/12/15
N2 - Remote sensing of canopy chemistry could greatly advance the study and monitoring of functional processes and biological diversity in humid tropical forests. Imaging spectroscopy has contributed to canopy chemical remote sensing, but efforts to develop general, globally-applicable approaches have been limited by sparse and inconsistent field and laboratory data, and lacking analytical methods. We analyzed leaf hemispherical reflectance and transmittance spectra, along with a 21-chemical portfolio, taken from 6136 fully sunlit humid tropical forest canopies, and developed an up-scaling method using a combination of canopy radiative transfer, chemometric and high-frequency noise modeling. By integrating these steps, we found that the accuracy and precision of multi-chemical remote sensing of tropical forest canopies varies by leaf constituent and wavelength range. Under conditions of varying canopy structure and spectral noise, photosynthetic pigments, water, nitrogen, cellulose, lignin, phenols and leaf mass per area (LMA) are accurately estimated using visible-to-shortwave infrared spectroscopy (VSWIR; 400-2500. nm). Phosphorus and base cations are retrieved with lower yet significant accuracy. We also find that leaf chemical properties are estimated far more consistently, and with much higher precision and accuracy, using the VSWIR range rather than the more common and limited visible to near-infrared range (400-1050. nm; VNIR). While VNIR spectroscopy proved accurate for predicting foliar LMA, photosynthetic pigments and water, VSWIR spectra provided accurate estimates for three times the number of canopy traits. These global results proved to be independent of site conditions, taxonomic composition and phylogenetic history, and thus they should be broadly applicable to multi-chemical mapping of humid tropical forest canopies. The approach developed and tested here paves the way for studies of canopy chemical properties in humid tropical forests using the next generation of airborne and space-based high-fidelity imaging spectrometers.
AB - Remote sensing of canopy chemistry could greatly advance the study and monitoring of functional processes and biological diversity in humid tropical forests. Imaging spectroscopy has contributed to canopy chemical remote sensing, but efforts to develop general, globally-applicable approaches have been limited by sparse and inconsistent field and laboratory data, and lacking analytical methods. We analyzed leaf hemispherical reflectance and transmittance spectra, along with a 21-chemical portfolio, taken from 6136 fully sunlit humid tropical forest canopies, and developed an up-scaling method using a combination of canopy radiative transfer, chemometric and high-frequency noise modeling. By integrating these steps, we found that the accuracy and precision of multi-chemical remote sensing of tropical forest canopies varies by leaf constituent and wavelength range. Under conditions of varying canopy structure and spectral noise, photosynthetic pigments, water, nitrogen, cellulose, lignin, phenols and leaf mass per area (LMA) are accurately estimated using visible-to-shortwave infrared spectroscopy (VSWIR; 400-2500. nm). Phosphorus and base cations are retrieved with lower yet significant accuracy. We also find that leaf chemical properties are estimated far more consistently, and with much higher precision and accuracy, using the VSWIR range rather than the more common and limited visible to near-infrared range (400-1050. nm; VNIR). While VNIR spectroscopy proved accurate for predicting foliar LMA, photosynthetic pigments and water, VSWIR spectra provided accurate estimates for three times the number of canopy traits. These global results proved to be independent of site conditions, taxonomic composition and phylogenetic history, and thus they should be broadly applicable to multi-chemical mapping of humid tropical forest canopies. The approach developed and tested here paves the way for studies of canopy chemical properties in humid tropical forests using the next generation of airborne and space-based high-fidelity imaging spectrometers.
KW - Canopy chemistry
KW - Carnegie Airborne Observatory
KW - Chemometrics
KW - Hyperspectral
KW - Imaging spectroscopy
KW - Partial least squares regression
KW - Rain forest
KW - Spectranomics
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U2 - 10.1016/j.rse.2011.08.020
DO - 10.1016/j.rse.2011.08.020
M3 - Article
AN - SCOPUS:81355127583
SN - 0034-4257
VL - 115
SP - 3587
EP - 3598
JO - Remote Sensing of Environment
JF - Remote Sensing of Environment
IS - 12
ER -