Colour Interpretation Guide


low water cloud

date
Meteosat Second Generation

length
Snow RGB - Recipe

author
Red: VIS0.8
Green: NIR1.6
Blue: IR3.9 refl

Fog, water clouds with large droplets on the cloud top

Fog and water clouds with large droplets on the cloud top appear light yellow with some greenish tones in the Snow RGB images.

Fog and low level water clouds over sea often consist of large droplets, because of the lower number of condensation nuclei. The image pair below (Snow and Day Microphysics RGB) shows traces of ship trails in maritime stratocumulus. Ships inject condensation nuclei, so along their trail the water clouds consist of smaller droplets. The ship trails are nicely seen in the Day Microphysics RGB image (greenish lines in the pink background) and also seen in the Snow RGB images: whitish lines (water cloud with smaller droplets) in the light yellow background (water cloud with large droplets).

water clouds
Snow RGB (left) and Day Microphysics RGB (right) for 07 March 2014 09:25 UTC

The image below shows another example of maritime water clouds with small and large droplets.

water clouds
Snow RGB (left) and Day Microphysics RGB (right) for 15 March 2014 09:25 UTC

Explanation of the colours of water clouds and fog with large droplets on the cloud top (see also the recipe on the left side):

• Compared to the water clouds with small droplets the reflectivity values decrease slightly in VIS0.8 and NIR1.6 and more strongly in IR3.9 channel. After the linear stretching and the gamma correction the green signal is usually the highest one (close to maximum), the red signal is slightly lower (but still strong) and the blue signal is much lower (but still stronger than medium). As a consequence water clouds with large droplets appear light yellow with some greenish tones.