Variations of Foliage Chlorophyll fAPAR and Foliage Non-Chlorophyll fAPAR (fAPARchl, fAPARnon-chl) at the Harvard Forest

In the last three decades, substantial advancements have been made in understanding the global carbon cycle. Some of these advancements involve using the fraction of absorbed photosynthetically active radiation (fAPAR) by an entire canopy (fAPAR(canopy)) and/or the Normalized Difference Vegetation Index (NDVI) in modeling studies. In spite of these advancements, large uncertainties still remain. Zhang et al. (Remote Sens. Environ., 2005) [1] tried to mitigate some of these uncertainties with the concept of using fAPAR that is restricted to the foliage chlorophyll (fAPAR(chl)) instead of the entire canopy. In this current study, we calculated fAPAR(canopy), fAPAR(chl), and foliage non-chlorophyll fAPAR (fAPAR(non-chl)) for the Harvard Forest using a radiative transfer model and multi-temporal Earth Observing One (EO-1) Hyperion satellite images. The canopy-level proportions of foliar chlorophyll and non-chlorophyll absorption were determined at different seasons (spring, summer, autumn) in an effort to demonstrate temporal variations of three plant functional types: deciduous forest, coniferous forest, and grass. Comparisons were made for NDVI versus fAPAR and for the Enhanced Vegetation Index (EVI) versus fAPAR(chl). In addition, EO-1 Hyperion images were utilized to simulate these new fAPAR(canopy), fAPAR(chl), and fAPAR(non-chl) products at 60 m as prototypes for the proposed NASA HyspIRI satellite spectrometer. These products should prove useful for future terrestrial carbon cycle and ecosystem studies.