FAPAR (Fraction of Absorbed Photosynthetically Active Radiation) is an important parameter for remote sensing monitoring plants net primary productivity (NPP) of land ecosystem. It is crucial that the calculated value approximates the actual value of canopy absorbed photosynthetically active radiation. The calculation accuracy directly influences the estimation of NPP and carbon cycle. The model in this paper is derived by analyzing the interaction processes between the photons and the canopy. It considers parameters like soil reflectance, canopy structure and solar zenith angle, etc. The relationship between these parameters and FAPAR is analyzed. The comparison results with Monte Carlo simulations and the validation results using field measurements prove the model to be accurate. We further choose Yingke, Zhangye City, Gansu province as study area, and retrieve LAI and FAPAR from hyperspectral and multi-angle PROBA-CHIRIS. Field data is also used to validate the retrieval result.

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