The Sentinel-4 L1b products include Earth radiance, Sun irradiance, DPPF (Data Processing Parameter File), stars data, and calibration products. Amongst these products, Earth radiance, Solar irradiance, and DPPF (to be confirmed) products are distributed to all users, whereas the other products are only available to Expert Users (users such as academics and industrial software engineers who have previous experience of similar EO missions).

The Sentinel-4 Level-0 to Level-1B data processing software in the MTG ground segment's IDP performs a number of key tasks:

• Process Level-0 data into Level-1b data products;
• Provide, in the level-1b data products, quality information on individual pixel level, spectrum level (per north-south viewing direction) and measurement level;
• Provide Level-1b data product metadata that allows fast and efficient searching of the data;
• Analyse and process all required measurement data in order to provide the necessary information to allow monitoring the performance and calibration of the instrument and its data products;
• Enable the calculation of new calibration key parameters (key data) for accurate Level-0 to Level-1B data processing of subsequent measurement data.

The Sentinel-4 Level-2 products are to be ready at the end of commissioning (i.e. day-1). The Level-2 data fields, field names, metadata, etc., will be defined per Level-2 product in the framework of ESA's Level-2 processor development for Sentinel-4, in line with the NetCDF Climate and Forecast (CF) Metadata Convention elaborated in the framework of MTG, and the INSPIRE (Infrastructure for Spatial Information in the European Community) Metadata Regulation convention. Table 2 lists the Sentinel-4 Level-2 products.

All Level-2 products depend on Sentinel-4 L1b radiance and irradiance data. For the generation of the Level-2 products in the MTG ground segment's L2P the following external auxiliary input are required:

• Pressure, temperature, humidity, and density fields from forecast data (in the case of forward processing) or from re-analysis data (in the case of reprocessing) from ECMWF (preferred option), or from a climatology (fall-back option);
• A static digital elevation model (to be specified);
• NO2 and O3 data used as a-priori information for the NO2 and O3 products from chemical forecast model fields e.g. from the Copernicus Atmosphere Monitoring Service (preferred option) or from a climatology (fall-back option);
• Snow / ice flags included in the Sentinel-4 L1b radiance product.

The FCI Level-2 Cloud Mask (Scenes Analysis) and Cloud Analysis product (SCE/CLA) or the FCI Level-2 Optimal Cloud Analysis (OCA) products are foreseen as possible optional inputs to the Sentinel-4 Level-2 processing. The usage of flags from the FCI SCE/CLA product has the potential of enhancing cloud and aerosol screening. The usage of the FCI OCA cloud product has the potential of enhancing the scattering correction in trace gas retrievals.