Satellite-Observed Reflectance of Snow and Clouds

Abstract

The effects of snow and cloud cover on bidirectional reflectance were examined using visible radiation (0.5?0.7 ?m) data measured by NOAA polar orbiting satellites between June 1974 and February 1978. Reflectances resulting from different cloud/snow cover conditions were compared using Northern Hemisphere snow cover maps, surface weather charts, satellite photos and data on land surface types. This was done for the prevalent surface types found in regions which, at certain times during the Northern Hemisphere winter, showed marked interannual variations in snow cover, None of the cases studied showed that concurrent cloud and snow cover produced significantly different reflectances than cloud cover alone. Cloud cover alone was found to yield higher reflectances (?0.62) than snow cover alone, with the difference being greatest over forested areas. Clear-sky reflectances over farming and grazing lands [snow (0.45), no snow (0.15)] were found to be significantly higher than those over forested regions [snow (0.33), no snow (0.11)]. Variations in satellite zenith angle wore not found to produce significant effects in most cases studied. Local viewing times at high latitudes for the polar orbiting satellites wore found to vary from 0800 to as late as 1200 LST.