Calculation of FAPAR over ragged terrains: A case study at Saihanba

Remote sense values of the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) suffer from the effect of ragged terrain. In this study, the effect of ragged terrain was internalized into the FAPAR model based on recollision probability (FAPAR-P), by improving FAPAR-P in two aspects: calculating the shielding factor to correct for the fraction of diffuse sky radiation to the total radiation, and correcting for the interception probability according to the slope and aspect of each pixel. Then, the new model FAPAR-PR (FAPAR-P Model for Ragged Terrain Area) was established. To validate the new model, we chose Saihanba National Forest Park of Hebei Province as the study area, and compared the FAPAR values derived from the models with FAPAR values measured in situ using photon flux sensors and the SunScan canopy analysis system (Delta-T Devices Ltd., UK). The validation result shows that the FAPAR-PR model is applicable to ragged terrain areas and achieves a high level of accuracy.