Global-scale comparison of OLCI remote sensing reflectance from sentinel-3A and -3B

The suite of Sentinel-3 missions from the European Union Copernicus programme is expected to provide long-term series of ocean color data from the Ocean and Land Colour Imager (OLCI) to monitor the state of the oceans. The consistency of the OLCI standard products is analysed by presenting a comparison of the level-2 daily remote sensing reflectance R R S data from Sentinel-3A and Sentinel-3B (S-3A and S-3B) at the pixel level over the global ocean and multiple years. Regardless of the camera number, a remarkable level of agreement is found for R R S and the aerosol products during the tandem phase, an early stage of the S-3B mission when the spacecraft was placed on the same orbit as S-3A. This agreement is degraded after S-3B reached its final orbit, with much more scatter in the comparison and the appearance of systematic differences between S-3A and S-3B data that depend on the camera pair considered. For the most eastern viewing cameras (3 to 5), R R S at short wavelengths and the aerosol optical thickness at 865 nm tend to be larger, and the Ångström exponent lower, than for the western viewing cameras (1 and 2). Possible impacts of the geometry of illumination and observation and of glint conditions are investigated. Further looking for elements that could explain cross-camera issues (knowing that they are similarly affecting both missions) and analyzing the behavior of the atmospheric correction in the near-infrared (starting with the aerosol products) are recommended avenues of investigation to improve the OLCI data record. • R R S and aerosol level-2 data from S-3A and S-3B are compared on a global scale. • S-3A and S-3B data show remarkable agreement during the tandem phase. • After the tandem phase, S-3A and S-3B data exhibit larger differences and biases. • R R S in the blue tends to be higher for cameras 4 and 5 than for cameras 1 and 2. • AOT in the NIR tends to be higher for cameras 4 and 5 than for cameras 1 and 2.