Cumulus Bands at Night

At night, the 3.9 and the 10.7 um channels behave similarly, since only emitted radiation is present. At times, this allows for the detection of cumulus and cumulus bands; such as when differences between surface and cloud temperatures allow for the easy identification of the cloudy area. However, when land surface and cloud temperatures are nearly the same, discriminating between cloud and ground is extremely difficult with information from only one IR channel.

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This is illustrated in the 3.9 um imagery, above, from over the Great Lakes, during the night of 7 Dec 1995. As the loop starts, notice the distinct difference between cloud (cumulus bands), ground and surface water. As the evening progresses, and the ground cools, the distinction between cloud and ground becomes less evident. This is not the case when the fog/stratus product is used, and the cumulus bands (water cloud) are easily detected over, and downwind from, the Great Lakes. In the fog/stratus product loop below, cumulus bands are white and cirrus cloud is black.

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