A model for instantaneous FAPAR retrieval: Theory and validation

The Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) is a critical input parameter to many climate and ecological models. Its calculation accuracy from remote sensing images directly influences the estimation of net primary productivity (NPP) and carbon cycle. This paper presents a hybrid model combining the characteristics of geometric optic model and radiation transfer model. It considers the illuminated and shadow area of the canopy and soil, as well as the multiple scattering between the canopy and soil. The Monte Carlo simulations of canopy FAPAR are also conducted and the results are compared with model results. In addition, we did the simulation of FAPAR daily change by the model and MC method, and compare the results with field measured daily data of FAPAR. All the results prove the model effective.