In this processing routine, a correspondence between the OLCI reference channel Oq and all other channels from OLCI and SLSTR is established. The principal aim of this routine is to gather all de-registration information computed in the previous modules and from auxiliary data files.

Correspondence relations between the OLCI Oqm reference channel and the other OLCI, SLSTR nadir and oblique view channels (applicable for m=1, ..., 5). The reference ortho-rectified geolocation information included in the Level 1 product is also represented

Correspondence between Oq and all other OLCI channels is given through information read in an instrument characterisation file. Correspondence between Oq and its equivalent channel in SLSTR (Su) is derived from the deformation model (modelled from sub-pixel shifts at GCP). Finally, correspondence between Su and all other SLSTR channels is obtained from another specific instrument characterisation file. The geographic coordinates from a pixel in an SLSTR IR image is obtained using the following steps.

1. Apply deregistration to the reference SLSTR Su channel.
2. Apply the deformation model.
3. Apply the ortho-geolocation information from the OLCI Oq channel.

In addition to computation of correspondence grids, a collocation step aims to establish a data structure, where all required SENTINEL-3 SYN Level-1 data are accessible and indexed on the OLCI reference grid. Since all pixels in the SENTINEL-3 SYN Level-1 grids are in the common swath of the OLCI and SLSTR channels, for any pixel in the reference grid there is always a corresponding pixel in each acquisition grid. Similarly, a global pixel classification section aims to merge OLCI and SLSTR cloud and surface flags.

Logical flow of correspondence between OLCI Oq and all other channels module