Fog & Stratus, MSG

Example of a MSG Fog and Stratus RGB

Description: Made from MSG infrared channel data, this RGB is designed and tuned for monitoring the evolution of nighttime fog and stratus. Secondary applications include detecting fires and low-level moisture boundaries and classifying clouds in general. Since the product is tuned for night conditions, its use during the day is very limited.

Coverage: Nighttime only

Channels: MSG 3.9-µm IR; 10.8-µm IR; 12.0-µm IR

Color scheme:

  • Low clouds are yellow to light green
  • Thick, high clouds are red
  • Thin, high clouds are dark blue to black
  • Land and sea surfaces are various colors


  • Fog and stratus often cannot be seen on infrared images at night because they blend in thermally with the background; this RGB enhances the fog/stratus signal
  • Is very important for transportation forecasting


  • Thin cirrus may obscure the view of fog and stratus
  • May be noisy and difficult to interpret in cold temperature environments (below approximately -10ºC)
  • Is difficult to detect thin radiation fog
  • The real area of fog/low stratus is always slightly larger than in the image due the 3.9-µm IR channel’s sensitivity to warm pixels around the fog periphery



MSG Fog and Stratus RGB Animation Over Southern Africa, 05 July 2003, 0000 to 0600 UTC
Click to play animation.

The green areas over the southern portion of Africa are either fog or stratus. Notice how the coverage increases throughout the night. When the sun rises toward the end of the loop, the low clouds turn red. That’s due to the solar reflection off the fog and stratus in the 3.9-µm infrared channel, which causes contamination. For this reason, the RGB is only useful during nighttime.


MSG Fog and stratus RGB product over South America, 0800 UTC 30 Jul 2001

In this RGB over South America, which of the labeled areas are fog and stratus? (Choose all that apply.)

MSG Fog and stratus RGB product over South America, 0800 UTC 30 Jul 2001, with the main features identified

The correct answer are C, D, and E.

The areas around C, D, and E are fog and stratus since they have a light green or cyan color. The reddish cloud is cirrus, which overlies a large area of stratus within the white enclosure.