fAPAR (fraction of Absorbed Photosynthetically Active Radiation) estimates at various scale

This paper reviews the several methods available for estimating the fAPAR, both at local and large scale. The fAPAR definition is first discussed with regards to the directionality of the incident radiation. Then, the several techniques to estimate fAPAR from local ground measurements are reviewed with emphasis on the sampling strategy. We then describe methodologies to upscale fAPAR measurements over larger spatial domains. The several medium resolution fAPAR products available at the global scale are then presented. These products are intercompared over a sample of sites representative of the global domain. Finally, the accuracy of the products is evaluated against the fAPAR values derived from ground measurements. Conclusions are drawn on the suitability of the current products for vegetation monitoring and modelling and ways of improvement are proposed.