Sentinel-2 L1C radiometric validation using deep convective clouds observations

In the frame of the European Space Agency (ESA) Scientific Exploitation of Operational Missions (SEOM) program new algorithms are developed to validate the Sentinel-2 level 1C (L1C) product radiometry, beyond the baseline algorithms used operationally in the frame of the Sentinel-2 Mission Performance Centre (MPC). In this context this paper presents the implementation of a Sentinel-2 radiometric validation approach based on deep convective cloud (DCC) observations. Due to their physical properties DCCs can be used to monitor the radiometric response degradation of the reflective solar bands of optical sensors. Their observation allows interband radiometry validation in the visible-near infrared (VIS-NIR) domain relatively to an a priori well calibrated reference band. We first present the selection of Sentinel-2 data acquired over DCC targets, as well as the tools and assumptions used for the modeling of the theoretical DCC radiometric response. The validation methodology is then thoroughly described and justified. It is based on the comparisons between the observed and the simulated top-of-atmosphere reflectance spectrum. Interband radiometric validation is performed through the statistical analysis of a large collection of individual observations. Results show the very good radiometric performance of Sentinel-2 with interband gains lower than 2%.