The separate georeference storage in Sentinel-3’s geodetic_in.nc file is mainly due to the satellite’s unique scanning tech. The SLSTR on Sentinel-3 has a complex scanning system that requires detailed geolocation steps. This involves creating a quasi-cartesian grid, calibrating tie-points, and accurately positioning the satellite’s orbit, among other things.
The reason for the complexity? Sentinel-3 needs to correct for things like the instrument’s deformations relative to the satellite platform, which affects the accuracy of the data. Plus, the SLSTR’s scan geometry is more complex than other sensors, making data reprojection and geolocation a bit tricky.
Storing georeferences separately gives more precision and flexibility in handling this data, especially considering the satellite’s changing position and Earth’s varied surface features.
