Description:

Using infrared channel data, this RGB detects ash, sulphur dioxide, and ice crystals from volcanic eruptions and can be used to track plumes over long distances downstream of an eruption site. The product helps forecasters track volcanic effluents and the information is used to provide warnings to aviation authorities and emergency managers. Note that the ash RGB is nearly identical to the dust RGB but has slightly different tuning (temperature difference thresholds and enhancement of individual red, green, blue inputs are slightly modified).

The current MODIS, MSG SEVIRI, and Suomi NPP imagers have the necessary channels to make this product. Future JPSS VIIRS, FY-3 MERSI-2, GOES-R ABI, Himawari AHI, FY-4 AGRI, and MTG FCI instruments will also have the needed channels for producing a day-night volcanic ash RGB.

Coverage: Both day and nighttime

Channels:

• Polar-orbiting satellites:
  
  • MODIS:
    Red: 12.0 minus 11.0 µm IR BT difference
    Green: 11.0 minus 8.55 µm IR BT difference
    Blue: 11.0 µm IR
  • Suomi NPP and future JPSS VIIRS:
    Red: 12.0 minus 10.8 µm IR BT difference
    Green: 10.8 minus 8.55 µm IR BT difference
    Blue: 10.8 µm IR
• Geostationary satellites:
  
  • MSG SEVIRI and future MTG FCI:
    Red: 12.0 minus 10.8 µm IR BT difference
    Green: 10.8 minus 8.7 µm IR BT difference
    Blue: 10.8 µm IR
  • Future GOES-R ABI:
    Red: 12.3 minus 10.35 or 11.2 µm IR BT difference
    Green: 10.35 or 11.2 minus 8.5 µm IR BT difference
    Blue: 10.35 or 11.2 µm IR
  • Future Himawari AHI:
    Red: 12.35 minus 10.45 or 11.2 µm IR BT difference
    Green: 10.45 or 11.2 minus 8.60 µm IR BT difference
    Blue: 10.45 or 11.2 µm IR
  • Future FY-4 AGRI:
    Red: 12.0 minus 10.7 µm IR BT difference
    Green: 10.7 minus 8.5 µm IR BT difference
    Blue: 10.7 µm IR

Color interpretation:

• Sulphur dioxide cloud is aqua-green (lower and middle latitudes) and yellow (at higher latitudes and for larger viewing angles near the edge of the full Earth disk)
• Depending on the height, temperature and particle size, ash goes from being bright red and pink (when it is very cold) to magenta (when it is warm) to yellow (when it is composed of very small ash particles)
• Thin cirrus appears black or dark blue
• High thick clouds and thunderstorms appear brown, with shades of orange and red for clouds composed of smaller ice particles
• Middle and lower clouds may appear in lighter shades of brown, blue, and green (at higher latitudes and for larger viewing angles near the edge of the full Earth disk)
• Blowing dust may appear as magenta
• Moist low levels, particularly the boundary layer, appear in bluish shades
• Surface features appear in lighter shades of blue, green, and dull magenta

Advantages:

• Shows the three major volcanic effluents (ash, sulfur dioxide, and ice crystals) in distinct colors, enabling users to observe effluents drifting from the site of an eruption

Limitations:

• Some everyday features can be mistaken for volcanic effluents
• Black cirrus can be a part of either volcanic or non-volcanic cloud systems
• Green clouds can resemble sulfur dioxide (especially noticeable at higher latitudes and for larger viewing angles near the edge of the full Earth disk)
• Limited detection of ash and sulfur dioxide when present with ice particles (mixed volcanic clouds)

Live data links:

• EUMETSAT Available Near-Real-Time Products, http://oiswww.eumetsat.org/IPPS/html/MSG/RGB/
• EUMeTrain, a site providing daily and archived satellite imagery, model output, case studies, and training resources, covering Europe, the Middle East, Africa, and North Polar Regions, http://eumetrain.org/

Additional information:

• EUMETSAT training materials
  
  • MSG Ash RGB Interpretation Guide, http://oiswww.eumetsat.org/IPPS/html/bin/guides/msg_rgb_ash.ppt
  • Volcanic Ash & SO₂ Detection, http://oiswww.eumetsat.org/WEBOPS/msg_interpretation/PowerPoints/Atmospheric/00_volcanic_ash_20060105.ppt
  • Monitoring of Volcanic Ash Eruptions With MSG RGB Products, recorded presentation: http://www.eumetsat.int/website/home/Data/Training/TrainingLibrary/index.html
  • MSG Channels Interpretation: Guide to weather, surface conditions and atmospheric constituents, http://oiswww.eumetsat.org/WEBOPS/msg_interpretation/index.php

References:

Caseadevall, T. J., 1994: Volcanic Ash and Aviation Safety: Proceedings of the First International Symposium on Volcanic Ash and Aviation Safety. U.S. Geological Survey Bulletin, 2047.

Prata, A. J., 1989: Observations of volcanic ash clouds in the 10-12 µm window using AVHRR/2 data. Int. J. Remote Sensing, 10 (4 and 5), 751-761.

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