Introducing Sentinel-2 Collection-1

Kurzfassung

The Copernicus Sentinel-2 satellite mission, with its Sentinel-2A and Sentinel-2B units, missions offers since several years now a massive quantitative and qualitative resource for the Earth observation community. Since the launch of Sentinel-2A in 2015, and Sentinel-2B in 2017, many lessons have been learnt leading to continuous improvements of the radiometric and the geometric performances. These performances are sufficiently mature now to initiate the reprocessing of the full archive (Collection 1). Indeed, the 30th of March 2021, the geometric refinement algorithm was introduced first over the Euro-Africa region and then in August 2022 worldwide, in order to improve the geometric performance of Sentinel-2 products based on the use of the Global Reference Image (GRI). Also, on the 25th of January 2022, a new processing baseline (PB 04.00) representing a major product evolution with a change of the product format was deployed. Among these changes there is the introduction of a radiometric offset to Level-1B, -1C and -2A products to avoid truncation of negative reflectances due to noise. At Level-1C, the radiometric alignment between Sentinel-2A and Sentinel-2B, the generation and grouping of the Level-1C quality masks in raster format and the addition of new atmospheric auxiliary parameters from ECMWF and Copernicus Atmosphere Monitoring Service (CAMS) are among the main improvements brought to the products. For the Level-2A products which inherit from these Level-1C evolutions, the additional main evolutions are upgrades on Cloud Screening and Atmospheric Correction algorithms. Indeed, the atmospheric correction can now rely on auxiliary data coming from the Copernicus Atmosphere Monitoring Service (CAMS) wherever not enough Dense Dark Vegetation pixels are present. For the reprocessing of the entire Sentinel-2 EO data archive, i.e. generation of the Sentinel-2 Collection- 1, a new version of the Level-1 processor will be used. This version, besides the major evolutions brought with the processing baseline 04.00 will also include: the handling of saturated pixels, the improvement of the technical quality masks and the use of Copernicus DEM at 30m resolution. Moreover, in view of the reprocessing campaign, the archive of geometric and radiometric calibration files has been updated. The validity start dates of radiometric and geometric calibrations have been optimized. The latest instrument spectral response function (ISRF) (updated twice since the beginning of the Sentinel-2 mission) will be used throughout Collection- 1. The radiometric harmonization of S2B on S2A introduced in PB 04.00 will also be applied on all Collection- 1. This paper reports on all the major improvements brought to the Sentinel-2 data from launch until now. The reprocessing campaign is expected to start inon the second quarter of 2022 and be available to the users by the end of 2023.