This false-color image shows the current extent of snow cover over the north-central and northeastern United States. This scene was acquired on January 2, 2001, by the Moderate-resolution Imaging Spectroradiometer (MODIS), flying aboard NASA's Terra spacecraft, and processed by the University of Wisconsin-Madison's MODIS direct broadcast receiving facility.
At visible wavelengths of light (e.g., 0.66 microns), snow cover is as bright as clouds and is therefore difficult to distinguish from cloud cover. However, at near-infrared wavelengths (e.g., 1.6 microns), snow cover absorbs sunlight and therefore appears much darker than clouds. This allows MODIS to discriminate between snow cover and clouds very effectively.
In this false-color image, land surfaces are green, water surfaces are black, snow cover is red, and clouds are white. Those clouds that contain a significant fraction of ice particles appear pinkish.