Sentinel-3 OLCI GI-FAPAR & rectified channels in O10, O11, O12 and O17 bands with uncertainties : algorithm theoretical basis document

Surface reflectances are important for monitoring land surfaces properties state and their changes. Two rectified channels were already operationally delivered in two bands as side products of Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) using the Sentinel 3 Ocean Land Colour Instrument (OLCI) data. We propose here two additional bands, O11 and O12, but also new coefficients values for O10 and O17 and the FAPAR itself as new spectral responses of OLCI on board Sentinel3A were published (OLCI SR, 2021). The so-called rectified reflectance values are virtual reflectances largely decontaminated from atmospheric and angular effects. This document summarizes the methodology and presents the results of the new coefficients for the normalization, i.e. angular effects correction, and atmospheric rectification processes over vegetated and bare soil pixels, respectively. We released also the coefficients for the Green Instantaneous FAPAR (GIFAPAR) to have consistency with the spectral response of OLCI on board Sentinel-3A.