Minimize Pre-Processing

The goal of pre-processing is to retrieve input data and condition it for subsequent Level-1C processing. Pre-processing uses the following steps:

  • Retrieval of all five OLCI images (along with their annotations) from Level-1B data and transformation to their acquisition geometry. The Level-1B images are on a specific grid, not accounting for some pixels in the overlapping areas of adjacent cameras. This step reconstructs the full images including the overlapping parts of each camera. Level-1B annotations are also retrieved. The output from this step is included in the final Level-1C product.
  • Retrieval of all SLSTR channels (along with their annotations) from Level-1B data and transformation to their acquisition geometry. The Level-1B grid was obtained by re-gridding Level-0 data. In this step, all the data are transformed back to their original acquisition geometry. Coarse along track boundaries of the SLSTR nadir and oblique view images are also computed to keep only the part of the SLSTR channels located within the OLCI images. Outputs from this step are SLSTR channels for the nadir and oblique part of the data. This data is also included "as-is" in the final Level-1C product.
  • The ortho-geolocation relative to an OLCI reference channel (Oq) is retrieved. Level 1B data only contains ortho-geolocation for a virtual OLCI channel whereas, for Level-1C processing, the ortho-geolocation for the specific reference channel is needed.
  • Ortho-geolocation of an SLSTR reference channel is retrieved. Similar to the OLCI Level-1B data, the SLSTR ortho-geolocation in Level-1B does not refer to a specific channel.
  • Conversion of OLCI and SLSTR radiometric units in Level-1B to TOA reflectance or normalised radiances for the reference channel.
  • Extraction of relevant ground control points from the database. Only those data points that lie within the OLCI images (minus a certain margin) are selected. Quality control of ground control points and subsequent rejection is also applied.

It should be noted that a preliminary Input Module has been added to take into account the different switches associated with the SYNERGY level and to verify the completeness of input files (not described here).

OLCI and SLSTR retrieval processing top level breakdown