Description:

This RGB is similar to true color in that it depicts surface and atmospheric features, such as vegetated areas, deserts, clouds, and ocean. But it is made from satellites without the requisite solar channels for true color, using a combination of visible and near-infrared channels instead. Many of the features have natural looking colors but some do not. For example, snow is cyan.

Currently (as of 2013), several polar-orbiting and one geostationary weather satellite have the needed channels to produce true a Natural Color RGB. Additional satellites, especially geostationary, will be coming online over the next decade with the necessary channels to allow for near global coverage. These include the upcoming U.S. JPSS polar-orbiting satellites, and the GOES-R, Japanese Himawari, Chinese FY-4, and EUMETSAT Meteosat Third Generation (MTG) geostationary satellites.

Coverage: Daytime only, requires solar reflectance information

Channels (red, green, blue):

• Polar-orbiting satellites:
  • Terra and Aqua MODIS:
    0.645 µm Vis; 0.856 µm NIR; 1.64 µm SWIR
  • NOAA and Metop AVHRR, FY-3 MERSI, Suomi NPP & future JPSS VIIRS:
    0.64 µm Vis; 0.865 µm NIR; 1.61 µm SWIR
• Geostationary satellites:
  • MSG SEVIRI:
    0.6 µm Vis; 0.8 µm NIR; 1.6 µm SWIR
  • Future GOES-R ABI, Advanced Himawari Imager (AHI), FY-4 AGRI, and MTG FCI:
    0.64 µm Vis; 0.865 µm NIR; 2.25 µm NIR

Color scheme:

• Low clouds are white
• Vegetation is green
• Deserts are reddish brown
• Snow cover and high ice clouds are cyan

For each of the three channels, a solar zenith angle correction is recommended to make the images brighter and enhance the contrast for low sun elevations present at high latitudes and during mornings and evenings.

Advantages:

• Does a good job of depicting many surface and near-surface features
• Provides an intuitive and compelling view of the Earth

Limitations:

• High ice clouds and snow cover are both cyan, making them hard to differentiate
• Thin cirrus clouds are difficult to detect

Live data links:

• CIRA/RAMMB Colorado State University Suomi NPP VIIRS Online site, http://rammb.cira.colostate.edu/ramsdis/online/npp_viirs.asp
• EUMETSAT Available Near-Real-Time Products page, http://oiswww.eumetsat.org/IPPS/html/MSG/RGB/

Loop:

This loop shows the day night terminator move across the scene, illustrating the product’s daytime-only use. The RGB is particularly useful for showing surface type, such as vegetation (green) and desert (reddish brown), and flooded areas (black).

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Example:

Since this RGB is based solely on solar channels, we see a large shadow area over the western Mediterranean Sea where a solar eclipse is centered. Notice that high clouds are cyan; low clouds are white; vegetation is green; and bare land and desert are brownish red.

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Exercise: