Basic idea behind RGBs

The three colors red, green and blue are allocated for three MSG channels or, if appropriate, channel differences. All other colors are generated as a combination of these three basic colors. The choice between channels and channel differences depends on the features that are being looked for.

This shall be demonstrated with the so-called Natural Color RGB, which is composed from the channels 03 (R), 02 (G) and 01 (B). Each of these three visible channels contains information about reflected sunlight (and consequently the optical thickness of clouds), but each channel also adds its own physical specialty:

Ch 03 (1.6 µm): particle phase and size (water, small and bigger ice droplets)
Ch 02 (0.8 µm): "greenness" of vegetation
Ch 01 (0.6 µm): optical thickness

The next figure shows the resulting colors for four typical features in the "Natural Color RGB"

Maximum signal from Ch 2: cloud-free; surface and vegetation dominates; resulting color: green
Medium values from all channels but Ch 3 dominates; no clouds or vegetation; resulting color: reddish
Medium values from all three channels; medium albedo - thick water cloud; resulting color: grayish
High values from ch 1 and 2 : high albedo; low counts from Ch 3: typical for ice cloud and/or snow; resulting color: cyan


When using RGBs, it is important to understand which qualities the individual channels or channel differences provide.