UNCERTAINTIES ASSESSMENT FOR MERIS/OLCI FAPAR

摘要

This paper describes the procedure for estimating thernuncertainties budget of the Fraction of AbsorbedrnPhotosynthetic Active Radiation (FAPAR) derived fromrnboth ENVISAT (Medium Resolution Instrument Sensorrn(MERIS) and Sentinel-3/Ocean Land Colour Instrumentrn(OLCI). This product is obtained from daily Top OfrnAtmosphere (TOA) data in the blue, red and nearinfraredrnspectral bands. The algorithm itself takes thernform of a set of several formulae which transformrncalibrated spectral bidirectional directional reflectancesrn(BRFs) into a single numerical value. These formulaernare designed to extract the direct green FAPAR in thernplant canopy and the rectified channels in the red andrnnear-infrared bands. Following the guidelines of QualityrnAssurance for Earth Observation (QA4EO) [1], thernuncertainties are estimated using the uncertaintiesrnpropagation theory which takes into account the onernassociated to the inputs, i.e. the spectral reflectancernmeasurements at the top of the atmosphere.rnMethodology and results using simulated data andrnactual MERIS data are presented.