Direct algorithm for mapping land surface FPAR from MODIS apparent reflectance at top of atmosphere

Fraction of abstracted Photosynthetically Active Radiation (FPAR) is a fundamental terrestrial state variable in most ecosystem productivity models and is also one of the key terrestrial products. This paper proposed a new Direct-Algorithm to retrieve FPAR from apparent reflectance of MODIS´s seven bands in the visible, near-infrared and short-wave wavelengths. The Direct-Algorithm developed from the dataset simulated by radiative transfer models of canopy and atmosphere with different canopy structures and atmosphere conditions, estimated direct FPAR (FPAR_dir), and scattering FPAR (FPAR_sct), and total FPAR of the canopy (FPAR_tot) by using linear equations of TOA reflectance. Result showed that the estimated FPAR product were close to that of MODIS products except the forest, perhaps because the homogenous canopy of the SAIL model is not suitable for the forest canopy.