The objective is the creation of high-quality METOP/AVHRR RGB images as similar as possible to the SEVIRI RGBs recommended by EUMETSAT.

Four RGB schemes were covered: Natural Color, Cloud, Day Microphysics and Night Microphysics RGBs. Their main features were discussed along with examples. They were compared to one another as well as SEVIRI RGBs.

Table 1 summarizes the information content of the discussed METOP AVHRR RGB types.

Cloud Surface Atmosphere
RGB Optical thickness Microphysics Temperature Vegetation Snow Temperature Moisture content
Day Microphysics X X X X X
Natural Color X X X X
Cloud X X X X
Night Microphysics X X X X X

Table 1: Information content of the four METOP/AVHRR RGB types

The Day Microphysics RGB is the best at cloud analysis for both scientific and forecast applications. It provides the most complex information about clouds. Different cloud types and surface objects have pronounced color contrasts.

Natural Colour RGB images convey the best information about vegetation. Cloud RGBs also provide data on vegetation but they combine it with temperature information and not with the 1.6 micron reflectivity. The color contrast of vegetated land against bare soil is much better and stable in Natural Colour RGBs (and bare soil is closer to its natural color).

For the public Cloud RGBs (in the convective season) and Natural Colour RGBs are the best. They are simple to interpret, and their colors are close to the natural ones.

The 'traditional' Cloud RGB is useful for high clouds. Thick and thin high-level clouds (e.g. the storm core and anvil) are easily discerned. However, Cloud RGB fares less well in winter because it shows almost no contrast between snow-covered land and water clouds/fogs.

The main purpose of the Night Microphysics RGB type is to distinguish fog and low clouds from cloud-free areas at night.

The effects of differences in scanning geometry were also discussed.

The RGB Colour Interpretation Guide on the EUMeTrain website provides examples of the typical colors of AVHRR color composites.