Training Module on METOP AVHRR RGB Images

• Chapter V: AVHRR Cloud RGB


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• Aim
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• Physical Basis
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• How to create Cloud RGB images
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• Typical Colors
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• Examples of Interpretation
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• Benefits and limitations
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• Comparison of AVHRR Cloud and SEVIRI HRV Cloud RGBs
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• Exercises

Aim

Cloud RGB images are created by combining data from three different channels. The 0.63 micrometer channel (VIS0.63) data is visualized in red, the 0.87 micrometer channel (NIR0.87) data in green and the 10.8 micrometer channel (IR10.8) data in blue. This is also a daytime RGB as it uses shortwave channels.

In cloudy areas it provides information on cloud thickness and cloud top temperature, and in cloud-free areas on green vegetation fraction ('chlorophyll content').

This RGB type is most useful during the convection period. The core and anvil of convective clouds are seen clearly. Thick and thin high-level clouds are easy to distinguish from each other and from other cloud types and land features, while mid- and low-level clouds and snow-covered land have similar colors.

Because the colors are (relatively) close to the natural colors of their respective features, images are easy to understand and convenient for the public.