Performance of Copernicus Sentinel-2 Level-2A processor Sen2Cor dependent on cloudiness

Abstract

The Copernicus programme is a European initiative for the implementation of information services dealing with environment and security, mainly based on observation data received from Earth Observation (EO) satellites. In the frame of this programme, ESA launched the Copernicus Sentinel- 2A and Sentinel-2B optical imaging satellites. These satellites deliver a new generation of optical data products designed to directly feed downstream services mainly related to land monitoring, emergency management and security. To ensure the highest quality of service for the Copernicus Sentinel-2 mission, ESA set up the Sentinel-2 Mission Performance Centre (MPC) supported by several Expert Support Laboratories (ESL). This presentation reports results of performance analysis of the Sentinel-2 Level-2A processor Sen2Cor performed by the ESL-L2A. Sen2Cor Level 2A processing is applied to Top-Of-Atmosphere (TOA) Level 1C ortho-image reflectance products. Sen2Cor L2A outputs are a scene classification image, aerosol and water vapour maps and the ortho-image surface reflectance (SR) product. SR is a Bottom-Of-Atmosphere (BOA) reflectance product corrected for the influence of the atmosphere. Scene classification is generated together with Quality Indicators for cloud and snow probabilities. Many earth remote sensing applications rely on time series of satellite data. However at many locations on the globe it is almost impossible to build time series relying only on cloudless data due the cloudiness of the region.. Generally time series get denser if they can include data containing some clouds. However, how accurate and reliable are L2A satellite products of cloudy images? To answer this question, the presentation is focused on providing Sen2Cor performance in dependence of cloud cover of the images. Sen2Cor performance of AOT and WV retrieval is analysed by direct comparison of Sen2Cor outputs with reference data provided by AERONET sunphotometers. Quality assessment of SR outputof Sen2Cor is based on AERONET corrected SR as reference. AERONET corrected SR are obtained by performing the atmospheric correction with in input the aerosol and WV information given by AERONET instruments. The analysis is performed within 9 km x 9 km area around the location of sunphotometer for more than 20 AERONET sites around the globe, covering different surface types, latitudes, climate zones and atmospheric conditions.