Hello, I would like if the (Reprojection) tab in Snap is used to simply change the reference coordinate system or is it used to do the radiometric correction with sentinel-3 data?
This is only used for reprojecting the data to a CRS. For OLCI there is no general radiometric correction- You can perform the Rayleigh Correction and the O2A Harmonisation. Both are located in the menu at
Optical / Preprocessing