Assessing BRDF effects of sun-induced fluorescence.. (FluorBRDF)
Assessing BRDF effects of sun-induced fluorescence for quantifying canopy-level photosynthetic efficiency
Start date: Jul 7, 2010,
End date: Jul 6, 2012
Over the past few decades, Earth-observation systems for land applications focused on deriving the type and/or status of green vegetation. Despite the fact that several missions are already dedicated to global vegetation monitoring, the derived information is mostly related to the amount of vegetation and not to the actual photosynthetic activity. There is, however, one additional source of information about photosynthetic activity in the optical domain that has not yet been exploited by any satellite mission. This source of information is related to the emission of fluorescence from the chlorophyll of leaves assimilating carbon. Measuring fluorescence from space would provide a direct measurement of the dynamics and actual functioning of the photosynthetic machinery. Within ESA’s FLEX demonstration mission, the University of Valencia undertook the first steps to acquire fluorescence measurements at canopy level. We propose a working package (FluorBRDF) that enforces a more robust spatially-explicit retrieval of fluorescence. FluorBRDF aims to account for bidirectional reflectance distribution (BRDF) effects, which is not only a function of sun-sensor geometry but also of the anisotropic properties of vegetation cover. Assessing and correcting for BRDF effects as induced by variations in vegetation canopy heterogeneity may lead to a more reliable measures. Challenges related to BRDF effect affecting the fluorescence signal brings us to the following objectives: i) to gain insights in the BRDF effects of the canopy-level emitted fluorescence signal on a theoretical basis using radiative transfer models, ii) to develop a methodology to correct for it. And finally, iii) to achieve higher accuracies of airborne fluorescence measures of heterogeneous canopies. This work will contribute to improved photosynthetic efficiency quantifications at canopy or ecosystem level.
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