Preprocessing optical data in remote sensing (RS) research usually describes the correction of sensor- and platform-specific radiometric and geometric distortions of RS data. Depending on the available data, this can include the following processing steps (not ordered):

• radiometric correction due to variations in scene illumination and viewing geometry
• geometric correcting /orthorectification to improve the positional accuracy of image data
• atmospheric correction to improve the spectral comparability between two scenes
• convertion of data into various units (e.g., TOA radiation to reflectance) or between different data types (e.g., .img to .tiff)
• compression or subsetting data to save disc space

Fortunately, both Landsat 8 and Sentinel 2 Level-1 products are already radiometrically and geometrically corrected. If you use Level-2 scenes, the atmosphere correction is already done on both products by the data provider, which is a prerequisite especially for a time series analysis. So there is no need for you to do either of this corrections any more!
We want to focus on converting the just-downloaded products into GeoTIFF files. A GeoTIFF file is a standard used in many GIS and RS software solutions and allows georeferencing information to be embedded within the TIFF-file itself. Such information includes the map projection, the coordinate system, the ellipsoid, the geodetic datum, the geospatial extent, and many more.

 

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