• The Cloud Phase RGB is sensitive to the snow grain size as two of its components (NIR1.61 and NIR2.25) are sensitive to it. The Cloud Phase RGB provides visual information about the snow reflectivity distribution and, through this, information about the snow grain size - more information than SEVIRI RGBs.

  • NIR2.25 is even more sensitive to snow grain size than NIR1.61. However, NIR2.25 images alone cannot be used to delineate snowy areas, as the snowy areas can be either brighter or darker than snow-free areas.

  • VIIRS NIR1.61 and NIR2.25 channel reflectivity values depend considerably on the viewing geometry (satellite zenith angle).

  • Snow in the Iberian Mountain Chain in the 11 January 2021, 12:05 UTC VIIRS Cloud Phase RGB image appears light blue instead of the 'usual' medium or dark blue, due to the almost continuous fine snow and large satellite zenith angle.

  • Analysing VIIRS Cloud Phase RGB images within given satellite zenith angle ranges, we found that the blue colour of the continuous snowy area became darker with time.