Several functions aimed at partitioning the pixels are identified and defined below:

• Classes of underlying surface, whatever the atmospheric conditions, on the basis of a priori knowledge from static or quasi-static atlas (currently land/saline water, fresh inland water (yes/no), high tidal activity areas (yes/no) and coastline (yes/no), that may evolve in the future).
• Pixels showing a risk of contamination by sun glint.
• Preliminary detection of cloudy pixels using simple brightness criteria.

The first type of classification is retrieved solely from the pixel geolocation information, while the second and third, being of a dynamic nature, are estimated from observation/illumination geometry and local wind conditions for the second, and from the measured radiance, taking account of the acquisition geometry, for the third. It is meaningful to split the classification process into three independent functions according to their required input data:

• APrioriClasses returns the a priori surface classes at the provided location.

• GlintRiskMask returns the possibility of sun glint (on water surfaces) according to current surface wind conditions and acquisition geometry.

• BrightMask returns the radiometrically based bright cloud classification from the input radiance at a given wavelength and the sun and view directions.