Cumuliform cirrus clouds
Ice clouds are usually seen in the Natural Colour RGB images because ice particles reflect the shortwave radiation. Ice clouds are depicted in cyan colour. Channels 1 and 2 contribute much more to the satellite measured radiation than channel 3A, because ice crystals strongly absorb in the 1.6 micron channel.
Cirrus clouds are high level clouds consisting mainly from ice crystals. They can have various structures and they typically consist of thicker and thinner parts. Thin cirrus clouds are semi-transparent letting some radiation coming through from below.
The MetOp AVHRR Natural Colour RGB image below (taken on 03 March 2014 at 06:43 UTC) shows cirrocumulus clouds. The underlying features (first of all the bright features – in the present case the snow covered mountains of Turkey and Armenia) can be seen ‘blurrily’ trough the thinner parts of the cirrocumulus cloud. Cirrus clouds could be recognized by their colour, structure and semi-transparent nature.
MetOp AVHRR image from 3 March 2014 at 06:43 UTC
Explanation of the cyan colour of cumuliform cirrus clouds in the Natural Colour RGB (see the recipe):
With a strong contribution of the green and the blue colour beam over sandy deserts, the resulting colour is cyan.