A Physical Explanation of the Correlation Between Albedo and Canopy Nitrogen
Mitchell
Andrew
Schull, Boston University, schull@bu.edu
(Presenting)
Liang
Xu, Boston University, bireme@gmail.com
Arindam
Samanta, Boston University, arindam.sam@gmail.com
Lucie
Lepine, University of New Hampshire, lucie.lepine@unh.edu
Scott
Ollinger, University of New Hampshire, scott.ollinger@unh.edu
Yuri
Knyazikhin, Boston University, jknjazi@bu.edu
Ranga
Myneni, Boston University, ranga.myneni@gmail.com
Recent studies have shown that there is a high correlation between canopy nitrogen and NIR reflectance and subsequently canopy albedo. We provide a physical explanation for the correlation using the spectral invariants of the radiative transfer. The spectral invariant approach allows for a very accurate parameterization of the canopy reflectance in terms of the wavelength dependant single scattering albedo and two spectrally invariant and structurally varying parameters- recollision and escape probabilities. The spectral invariant parameters depend on macro–scale structural features such as crown shape and size, the proportion of sunlit and shaded leaves and ground cover, as well as micro-scale information such as within crown foliage distribution. We retrieve the spectral invariant parameters from Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) hyperspectral data for 3 sites in New England and 2 sites in the southeastern United States for which ground data on canopy %N were available. Theoretical and statistical analyses showed that canopy structure is highly correlated to canopy albedo, R2=94, suggesting that canopy structure is a dominant factor causing observed variation in NIR albedo. We therefore hypothesize that the amount of canopy %N may have an indirect impact on NIR albedo through the formation of macro-scale features. We provide further analysis by removing the effects of canopy structure from the measured signal. Finally we show that we can predict %N more accurately using the macro-scale features than canopy albedo indicating that competing factors at the leaf and canopy scales are imbued in the measured albedo signal.
Presentation Type: Poster
Poster Session: Ecosystems Science
NASA TE Funded Awards Represented:
Knyazikhin, Yuri
Vegetation Biophysical Parameter Suite from MISR for Ecological Applications