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Copernicus Sentinel-2: Major Products Upgrade Upcoming
Copernicus Sentinel-2: Major Products Upgrade Upcoming
29 September 2021
As anticipated in the Sentinel-2 Mission Status Report, ESA is pleased to confirm the forthcoming upgrade of Sentinel-2 products.
This evolution includes major updates on the products format with respect to the current baseline (PB 03.01; PSD version 14.6). The Processing Baseline 04.00 will tag every new product generated with this evolution and for all product types.
The deployment on the operational production is planned to occur on 26 October.
Regarding Level-1C products, the following evolutions will be included:
- Correction of the radiometric bias between Sentinel-2A and Sentinel-2B (keeping Sentinel-2A as reference): Sentinel-2A and Sentinel-2B radiometric cross-calibration results have highlighted a small bias for VNIR bands B01 to B09. This radiometric difference will be mitigated by applying a radiometric bias correction of 1.1% to Sentinel-2B VNIR bands B01 to B09.
- Generation of the Level-1C quality masks in raster format: Instead of the current GML format, the Level-1 quality masks will be provided in raster format (coded in JPEG2000). The masks will be grouped in 3 categories as defined as follow:
- MSK_CLASSI: A band-independent raster file composed of the classification masks i.e. the cirrus and opaque clouds. This mask will be defined at a spatial resolution of 60 m.
- MSK_QUALIT: For each spectral band, a raster file composed of all the radiometric and technical quality masks. For each spectral band, the mask will be defined at the same spatial resolution as that of the spectral band.
- MSK_DETFOO: separately, for each spectral band, a 1-byte raster file using 4 bits to encode the 12 detector footprints. For each spectral band, the mask will be defined at the same spatial resolution as that of the spectral band.
- Addition of the following ECMWF (European Centre for Medium-Range Weather Forecasts) parameters: u/v wind components (10u and 10v) and relative humidity (r). The format of the AUX_ECMWFT file will remain unchanged.
- Addition in the product of the following CAMS (Copernicus Atmosphere Monitoring Service) parameters: Total Aerosol Optical Depth at 550 nm (aod550), Surface Geopotential (z), Black Carbon Aerosol Optical Depth at 550 nm (bcaod550), Dust Aerosol Optical Depth at 550nm (duaod550), Organic Matter Aerosol Optical Depth at 550 nm (omaod550), Sea Salt Aerosol Optical Depth at 550 nm (ssaod550), Sulphate Aerosol Optical Depth at 550 nm (suaod550), Total Aerosol Optical Depth at 469 nm (aod469), Total Aerosol Optical Depth at 670 nm (aod670), Total Aerosol Optical Depth at 865 nm (aod865) and Total Aerosol Optical Depth at 1240 nm (aod1240). The AUX_DATA folder embedded in the Level-1C products will contain the CAMS forecast data for that specific tile in a single dedicated GRIB file named as AUX_CAMSFO.
- Addition of Level-1C snow/ice mask: This new SNOICE mask will be computed as raster file in JPEG2000 format. The snow/ice mask will be included in the MSK_CLASSI. The snow percentage will also be added into the Quality_Indicators_Info section of the L1C Tile metadata.
- Provision of negative radiometric values (implementing an offset):A radiometric offset will be added up to the image reflectance at Level-1C. The dynamic range will be shifted by a band-dependent constant, i.e. RADIO_ADD_OFFSET. From the user’s point of view, the L1C Top of Atmosphere (TOA) reflectance (L1C_TOA) shall be retrieved from the output radiometry as follows:
- Digital Number DN=0 will remain the “NO_DATA” value
- For a given DN in [1;215-1], the L1C TOA reflectance value will be: L1C_TOAi = (L1C_DNi + RADIO_ADD_OFFSETi) / QUANTIFICATION_VALUEi
- Addition of the DOI (Digital Object Identifier) in the Level-1C metadata: A DOI is a string of numbers, letters and symbols used to permanently identify a document and/or a dataset and to create a link to it on the web. The DOI URL will be reported in a new field in the General_Info section of the Datastrip and User Product Metadata.
Regarding the Sentinel-2 Level-2A products, the first five above-mentioned evolutions are directly inherited from the corresponding Level-1C product. Additional evolutions will be included as summarised hereafter:
- Provision of negative radiometric values (implementing an offset): Similarly to Level-1C, the dynamic range will be shifted by a band-dependent constant, i.e. BOA_ADD_OFFSET. From the user’s point of view, the L2A Bottom of Atmosphere (BOA) reflectance (L2A_BOA) shall be retrieved from the output radiometry as follows:
- Digital Number DN=0 remains the “NO_DATA” value
- For a given DN in [1;215-1], the L2A BOA reflectance value will be: L2A_BOAi = (L2A_DNi + BOA_ADD_OFFSETi) / QUANTIFICATION_VALUEi
- Provision of Band 01 at 20 m spatial resolution: Band 01 will be added with 20 m resolution (in the 20 m resolution image folder) in addition to the native 60 m resolution.
- Addition of Level-2A Quality Indicators (new fields in the tile metadata and additional xml L2A_QI_report in the QI_DATA folder): New Quality Indicators CLOUDY_PIXEL_OVER_LAND_PERCENTAGE, AOT_RETRIEVAL_METHOD, GRANULE_MEAN_AOT, GRANULE_MEAN_WV, OZONE_SOURCE, and OZONE_VALUE, will be added in the Level-2A tile metadata in the Quality_Indicators_Info section. In addition, Quality Indicators providing information on the Scene Classification, Atmospheric Correction and Auxiliary Data will be reported in a new L2A_QUALITY.xml report in the QI_DATA folder of the tile.
- Aerosol correction using CAMS auxiliary data: The Level-2A processor will use the CAMS Total Aerosol Optical Depth (AOD) at 550 nm when Dark Dense Vegetation (DDV) pixels are missing in the image. This improvement will mitigate the chess-board effect that is sometimes visible between tiles.
- Improvement of the bright target classification over coastal areas: The cloud detection over coastal areas of bright targets (e.g. buildings and bright sand) is improved to mitigate against false detections.
- Improvement of the topographic and casted shadows: The class “dark features and shadows” (SCL = 2) is replaced by “topographic and casted shadows” (keeping code SCL = 2), while dark features pixels will be re-assigned to the “unclassified” class (SCL = 7).
- Improvement of clouds and cloud shadows detection:Thanks to the use of the Sentinel-2 MSI parallax properties between bands B08 (resampled at 20m) and B8A (20m native resolution), the accuracy of the cloud detection algorithm has been improved, reducing the false clouds detection of bright targets - especially in urban areas - as well as reducing the snow false detection in high altitude clouds. Also, the cloud shadow algorithm benefits from using the parallax properties, by retrieving an estimate of the cloud top-height to improve the localization of clouds shadows on ground.
- Addition of the DOI (Digital Object Identifier) in the Level-2A metadata: Similarly to Level-1C product, a DOI will be reported in a new field in the General_Info section of the Datastrip and User Product Metadata.
Detailed information on the changes implemented are provided in dedicated sections of version 14.8 of the Products Specification Document (PSD). The corresponding XSD schemas are provided together with the document as PDF attachments.
We invite users to adapt their applications for compatibility with this evolution. Sample products representative of Processing Baseline 04.00 will be made available in the coming days.
A compatible update of the SNAP Software will be made available by the time of the transition. Backward compatibility with previous formats will be maintained.