Level-1 processing uses consolidated Level-0 data as input.

• Level-1A processing is focused on decompressing relevant mission source packets. The Level-1A product is not available to Users.
• Level-1B processing uses the Level-1A product and applies the required radiometric corrections. The Level-1B product is not available to Users.
• Level-1C processing uses the Level-1B product and applies radiometric and geometric corrections (including orthorectification and spatial registration).

Level-1B

The Level-1B processing sequence is broken down into the following steps:

1. Level-1B radiometric processing, including:
   • dark signal correction
   • pixel response non-uniformity correction
   • crosstalk correction
   • defective pixels identification
   • high spatial resolution bands restoration (de-convolution and de-noising).  This correction is disabled by default in the Level-1B processing.
   • binning of the 60 m spectral bands.
   • adding of the radiometric offset.
2. Resampling on the common geometry grid for registration between the Global Reference Image (GRI) and the reference band (B4 by default).
3. Collection of the tie-points from the two images for registration between the GRI and the reference band.
4. Tie-points filtering for image-GRI registration: filtering of the tie-points over several areas. A minimum number of tie-points is required.
5. Refinement of the viewing model using the initialised viewing model and and Ground Control Points (GCPs). The output refined model ensures registration between the GRI and the reference band.
6. Level-1B imagery compression utilises the JPEG2000 algorithm.

Level-1C

Level-1C processing includes radiometric and geometric corrections including ortho-rectification, add of the radiometric offset and spatial registration on a global reference system with sub-pixel accuracy.

Level-1C processing is broken down into the following steps:

1. Tiles association: selection of pre-defined tiles intersecting the footprint of the required image.
2. Resampling grid computation: enabling linking of the native geometry image to the target geometry image (ortho-rectified).
3. Resampling of each spectral band in the geometry of the ortho-image using the resampling grids and an interpolation filter. Calculation of the TOA reflectances also occurs in this step.
4. Quality masks computation in raster format: MSK_CLASSI (opaque cloud, cirrus and snow), MSK_QUALIT (lost ancillary packets, degraded ancillary packets, lost MSI packets, degraded MSI packets, defective pixels, no data, partially corrected crosstalk, and saturated pixels) and detector footprints masks are generated.
5. Imagery compression of the resultant Level-1C imagery via the JPEG2000 algorithm