Initial Validation of Sentinel-2 Collection-1 L2A-Products

Abstract

The Copernicus Sentinel-2 mission provides data since the launch of the Sentinle-2A unit in 2015. With the launch of the Sentinel-2B in 2017 it is a constellation of two polar orbiting satellite units. Both Sentinel-2A and Sentinel-2B are equipped with an optical imaging sensor MSI (Multi-Spectral Instrument) which acquires high spatial resolution optical data products. The Sentinel-2 mission serves for observation of land-cover change and deriving biophysical variables related to agriculture and forestry, monitors coastal and inland waters and is useful for risk and disaster mapping. Atmospheric correction processor Sen2Cor was developed to remove the effect of the atmosphere from Sentinel-2 data. Sen2Cor is designed for mono-temporal processing of Sentinel-2 L1C data products providing Level-2A Bottom-of-Atmosphere (BOA) surface reflectance product together with Aerosol Optical Thickness (AOT), Integrated Water Vapour (WV) and Scene Classification (SCL) maps. Since June 2017, ESA uses Sen2Cor for systematic, operational Level-2A processing of Sentinel-2 acquisitions. Products are available on the Copernicus Open Access Hub. However, several evolutions of Sen2Cor and L2A-products since 2017 resulted in a quite inhomogeneous time series. Therefore, ESA started a reprocessing campaign of the complete Sentinel-2 data archive. The resulting Collection-1 of Sentinel data archive provides a real homogeneous time series based on the recent Sen2Cor processor version. The presentation provides initial validation results for AOT, WV and (BOA) surface reflectance retrieval together with quality assessment of cloud screening. Accuracy and uncertainty of AOT and WV retrieval is assessed with reference measurements from AERONET stations. BOA reflectance retrieval can be estimated on a limited number of reference data only from RadCalNet-sites and in-situ campaigns. Reference data for cloud screening are generated by manual labelling of test images.