Snow Cover

NASA's Terra Satellite Confirms a less Snowy Winter
NASA-GSFC News Release, July 29, 2000

If you think there was less snow on the ground this spring than usual in parts of the Midwest and western United States, Terra satellite data agree with you. Early results from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA's Terra satellite clearly observed a lot less snow cover than normal. Dr. Dorothy K. Hall will present results from MODIS at the International Geoscience and Remote Sensing Symposium (IGARSS) today in Hawaii. "The winter of 1999-2000 brought relatively little snow cover to parts of the North American continent, and the snow melted early as compared to normal years. Low snow cover can result in drier soil conditions, affect crop production, and lead to wildfires," Hall noted. Using data from MODIS and other satellites, scientists can determine the extent of spring snowcover which can be a harbinger of flood or drought conditions.

The MODIS composite snowcover map, derived from data taken over an 8-day period between March 5 and 12, depicts the snow line into Canada, in the provinces of Saskatchewan and Manitoba. Only scattered snowcover existed over parts of the northern United States, though the mountains were still snow covered. According to the National Oceanic and Atmospheric Administration's National Environmental Satellite, Data, and Information Service (NOAA/NESDIS) the average March snow line would normally extend from New England through the Midwest including southern Wisconsin, to southern portions of North Dakota. The snow line then normally continues farther south in the western states including the Rocky Mountains and west into the Cascades and the Sierras. NOAA/NESDIS has been producing weekly snow maps of the Northern Hemisphere land surfaces since 1966 using visible-band satellite imagery. Because snow has such a high reflectivity compared to other surfaces on Earth, snow covered areas appear much brighter in satellite imagery than most other surface types. However, Dr. Hall noted that the key difference between the MODIS-produced snow maps and the images produced by NOAA/NESDIS is that "MODIS has a higher resolution and an improved ability to discriminate between snow and clouds."