The fraction of photosynthetically active radiation (PAR) absorbed by green elements (FPAR) is an essential climate variable in quantifying canopy absorbed PAR (APAR) and gross and net primary production. Current satellite FPAR products typically correspond to black-sky FPAR under direct illumination only, but the radiation transfer and vegetation absorption processes differ for direct and diffuse PARs.

Dr. LI Wenjuan and Prof. FANG Hongliang, Institute of Geographic Sciences and Natural Resources Research (IGSNRR), Chinese Academy of Sciences, developed a new approach to estimate direct, diffuse, and total FPARs, separately, from Landsat surface reflectance data. Field-measured direct and diffuse FPARs were first derived for crops, deciduous broadleaf forests, and evergreen needleleaf forests at six FLUXNET sites. The differences between the Landsat-estimated and the field-measured FPARs are less than 0.05 (10%). The diffuse FPAR is higher than the direct FPAR by up to 19.38%, whereas the total FPAR is larger than the direct FPAR by up to 16.07%. The approach described here can be extended to estimate direct, diffuse, and total FPARs from other satellite data, and the obtained FPAR variables could be helpful to improve modeling of vegetation processes.

This work was supported by the Chinese Academy of Sciences and the National Natural Science Foundation of China.

The study has been published in the recent issue of Journal of Geophysical Research: Biogeoscience.(Li, W., & Fang, H. (2015). Estimation of direct, diffuse, and total FPARs from Landsat surface reflectance data and ground-based estimates over six FLUXNET sites. Journal of Geophysical Research: Biogeosciences, 120, 96-112. http://dx.doi.org/10.1002/2014JG002754 ).