Atmospheric correction Atmospheric correction is based on the 5S radiative transfer model. Atmospheric transmittance is estimated from water vapour, oxygen and ozone data. Correction factors are applied according to the calculated optical path length for each pixel. Cloud detection Cloud contamination in the image is automatically flagged for each pixel using four separate methods based on comparisons of the pixel values in different bands and the local gradient of pixel values. A composite mask is created using the logical OR of the flags.
Chip matching Both vector and raster matching is performed.
A similar principle is used for image matching. Geometric modelling Using ground control points a geometric model is used to recalculate the ephemeris and fit a low-order polynomial to the residual errors. Resampling To build mosaics, multiple scenes are resampled into a geographic template in Albers equal area projection.