ADDS - Aviation Digital Data Service

ADDS - Satellite Help Page (2 of 3)
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  • What do the numbers on the images mean?
    The answer depends on the channel so you may want to read the item below this one for more details on channels. The Visble channel displays albedo or reflectance expressed as a percentage. For example, a bright white shade may indicate 70% albedo. The Infrared (IR) channel is calibrated to temperature and expressed in degrees Celcius. Where clouds exist, the temperature is that of the tops of clouds. Where clouds do not exist, the temperature is that of the ground or the ocean. This information could be very valuable to aviators since clouds with tops below 0°C, may indicate that an Icing hazard exists. [An icing hazard could also exist in clouds warmer than freezing particularly if there is a strong temperature inversion beneath the cloud.] The Water Vapor channel is also calibrated to temperature in degrees Celcius. Interpreting the actual values displayed on the water vapor images is not useful.
  • What do the different channels show?
    The latest generation of GOES weather satellites (GOES-8,9,10) all carry 5 imaging sensors. They are in the following portions of the electromagnetic spectrum:
    • Channel 1: Visible (0.6 microns)
    • Channel 2: Shortwave Infrared (3.9 microns)
    • Channel 3: Water Vapor (.67 microns)
    • Channel 4: Infrared (11 microns)
    • Channel 5: Infrared (12 microns)
    These web pages provide images from channels 1, 3, and 4 which are generally the most useful to aviators and meteorologists. More details in plain English, please. The other 2 channels can be quite useful to scientists and developers of new products. (An example where all 5 channels are used in an aircraft icing application can be found at Research Applications Program of NCAR.)