Why does sentinel 3 store the geometry separately


I am curious why it is necessary to store the georeferences separately in the geodetic_in.nc file.

I found in https://sentinel.esa.int/documents/247904/4598082/Sentinel-3-SLSTR-Land-Handbook.pdf/ on page 19 that the reason for that is the conical scanner on the satellite.

However, I do not get it completely. I see that the recording is performed on a curve through the images (the ones provided at the end). But if I understand it correctly, the final georeferences in the geodetic_in.nc file are a choice and the the actual data is reprojected to these georefernces via nearest neighbor. Why do these georefences need to be irregular?

Thank you

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.