Training Module on METOP AVHRR RGB Images

• Chapter II: AVHRR Night Microphysics RGB


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• Aim
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• Physical Basis
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• How to create Night Microphysics 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 and SEVIRI Night Microphysics RGB images
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• Exercises

Benefits and limitations

The benefits of the Night Microphysics RGB:

• Provides full cloud analysis at night.
• Detects fog and low-level water clouds (with good color contrast).

Limitations:

• The IR3.74 brightness temperature values of high and very cold clouds are often noisy, resulting in green dots in the reddish-brown ice clouds. Therefore this RGB is not recommended for nighttime convection analysis. The IR10.8 single channel is more appropriate for this purpose.
• Extremely thin water cloud or fog might not be detected by the Night Microphysics RGB.
• Night Microphysics RGB might not detect all water clouds (or fog) at twilight, because then the IR3.74 channel also contains some solar radiation.