The OLCI FAPAR Land Product
This paper describes the procedure for retrieving the fraction of photosynthetic active radiation (PAR) absorbed by the vegetated terrestrial surfaces from an analysis of the Top Of Atmosphere (TOA) data acquired by the future Ocean Land Colour Instrument (OLCI) on board Sentinel-3. The proposed algorithm takes the form of a set of several formulae which transform calibrated spectral directional reﬂectances into a single numerical value. These formulae are designed to extract the green Fraction of Absorbed Photosynthetic Active Radiation (FAPAR) in the plant canopy from the measurements and the rectiﬁed channels in the red and near-infrared bands. The methodology described here has been optimized to assess the presence on the ground of healthy live green vegetation. This algorithm delivers, in addition to the FAPAR product, the so-called rectiﬁed reﬂectance values in the red and near-infrared spectral bands. These are virtual reﬂectances largely decontaminated from atmospheric and angular eﬀects. These two virtual reﬂectances can be also computed over bare soils using speciﬁc coeﬃcients. It also provides a categorization of pixel types thanks to a pre-processing identiﬁcation based on multi-spectral properties and the uncertainties estimates at a pixel level. The foreseen validation plan will then be summarized.