Using Channel 2 (3.9 µm) Imagery to Help Discriminate Snow & Cloud Cover

  The GOES-9 visible image below shows the western U.S. following a snowstorm that left a large path of snow on the ground, extending from CO to WI.   Visible imagery alone is often insufficient in defining the boundaries of snow swaths, because both clouds and snow are highly reflective at visible wavelengths.   Furthermore, if the cloud and the snow field have similar temperatures, the 10.7 µm detector (Channel 4, to be discussed later) will not necessarily distinguish between them either (see below).

  Because liquid water clouds are reflective at 3.9 µm, and snow fields are not, imagery from the 3.9 µm channel, in conjunction with the visible imagery, can reveal both snow fields and the low-level clouds over those snow fields.   In the 3.9 µm image below, snow appears as a dark gray and liquid water clouds are white.   Using both the visible and the 3.9 µm images, the extent of the cloud cover in southeastern NE and northeastern KS is clearly defined, as is the snow swath, which begins in eastern CO and continues through western KS, southeastern NE, IA and southern WI.

Click on any of the following images to view in their original 640 x 480 resolution
VIS3.9 µm 10.7 µm