Using Channel 2 (3.9 µm) and Channel 4 (10.7 µm) Imagery to Identify Night-time Fog
By subtracting the brightness temperatures of Channel 2 from those of Channel 4, we can produce an image, like the one below, that distinguishes fog and low-lying stratus clouds from other clouds and snow cover. The physics behind this algorithm are described in the CIRA-RAMM Team's GOES Advanced Imagery Applications Tutorial.
In this night-time fog product example, the areas of fog and stratus are clearly seen to be brighter than the land features over NV, northeast CA and southwest OR, which seemed so prominent in the comparable Channel 2 image. To compare these two images directly, click on the "FORWARD" loop control above. Go back to the Channel 2 "fog" image discussion.