|
Monitoring canopy structure and leaf biochemistry using multiangle and hyperspectral data
Yuri
Knyazikhin, Boston University, jknjazi@bu.edu
(Presenter)
Philip
Lewis, University College London, p.lewis@ucl.ac.uk
Mathias
Disney, University College London, mat.disney@gmail.com
Pauline
Stenberg, University of Helsinki, pauline.stenberg@helsinki.fi
Matti
Mottus, University of Helsinki, matti.mottus@helsinki.fi
Yan
Yang, Boston University, yangyannn@gmail.com
Miina
Rautiainen, University of Helsinki, miina.rautiainen@helsinki.fi
Mitchell
Schull, USDA-ARS Hydrology & Remote Sensing Lab, bucricket@gmail.com
Ranga
Babu
Myneni, Boston University, ranga.myneni@gmail.com
Recent studies indicated that for temperate and boreal forests there is a strong positive correlation between the BRF at NIR wavelengths and the foliar nitrogen concentration, %N. The significance of this result, if true, is three-fold. First, it would indicate an additional and overlooked role for nitrogen in the climate system via its influence on the surface albedo, and thus, biosphere - atmosphere interactions. Second, it may offer a simple and effective approach for monitoring foliar nitrogen using broadband satellite data. Finally, it may serve as the basis for a new parameterization of surface albedo that would provide a natural link to ecosystem processes. However, we show that the reported correlation is an artifact resulting from variations in canopy structure rather than %N. We found that this is true for all wavelengths of the solar spectrum. The impact of the canopy structure therefore can be strong enough to suppress the sensitivity of hyperspectral canopy reflectance to the leaf scattering properties, which is the only optical variable that conveys information about leaf interior, and results in spurious relationships between leaf biochemical constituents and the measured surface reflectance. We identified a new structural variable, the directional area scattering factor (DASF), which is an estimate of the ratio of the leaf area that forms the canopy boundary, as seen along a given direction, to the total leaf area. The DASF varies between 0 and 1, explains variation in BRF due to variation in 3D canopy structure and is sensitive to species composition. This variable provides information critical to accounting for structural contributions to measurements of leaf biochemistry from hyperspecral data. The goal of this poster is to introduce DASF, demonstrate its critical role in retrieving leaf biochemistry and present an algorithm for retrieving DASF and leaf biochemical constituents from Hyperion and MISR data.
Presentation:
2013_Poster_Knyazikhin_56_96.pdf (2394k)
Presentation Type: Poster
Session: Poster Session 2-B
(Wed 4:30 PM)
Associated Project(s):
Poster Location ID: 56
|