NOAA 99-32
Contact: Patricia Viets


From the vantage point of the Earth, it's easy for the human eye to distinguish snow and ice from clouds and fog. But to the eye of a weather satellite 500 miles above the Earth, it's quite a challenge.

Scientists at the Commerce Department's National Oceanic and Atmospheric Administration have developed a new method to distinguish snow and ice from clouds and fog in satellite imagery. It will mean more accurate weather observations, forecasts, and climate data

"NOAA's newest polar-orbiting satellite, NOAA-15, has a new channel that its predecessors did not," explained Rob Fennimore of NOAA's National Environmental Satellite, Data, and Information Service"The 1.6 micron channel on an instrument called the Advanced Very High Resolution Radiometer permits improved snow, ice and cloud discrimination. We've been testing the new channel since March 10."

Fennimore, George Stephens, and their colleagues have developed an image-processing technique that uses the new 1.6 micron channel, the 0.63 micron visible channel, and the 11.0 micron thermal channel to differentiate snow and ice from clouds and fog. The process renders the snow and ice white and most other surface features in natural colors. Low clouds are yellow; higher clouds range from yellow through green to light blue as the cloud temperature decreases.

The new methods have resulted in the production of some dynamic satellite images of the Great Lakes, Rockies, the Gulf of Saint Lawrence, Western Canada, and the Bering Sea"These cover the gamut of scene types," Fennimore said"With the five images, we have spanned the test period for the 1.6 micron channel quite nicely."

All scenes contain snow. The Great Lakes image contains lakes, farm/grassland, and forest. The Rocky Mountains image contains mountains, forest, and farm/grassland. The Gulf of St. Lawrence image shows forest, and sea/ice. The image of Western Canada shows mountains, forest, and tundra. And the image of the Bering Sea shows sea/ice and tundra.

The images can be viewed at:

Testing of the new channel ended April 20, and routine operational use of its snow detection capabilities will begin next winter when a new satellite exactly like NOAA-15 is scheduled for launch. The imagery will be used to generate snowcover maps for the National Weather Service's forecasting applications. The imagery will also be used to create special images covering significant snow and ice events. These images will be similar to the example images presented here.