A new data base: a digital archive of northern hemisphere snow cover

The purpose of this paper is to acquaint the research and user community with a new data base, a digitized archive of Northern Hemisphere snow cover. Weekly snow and ice charts have been prepared by the Synoptic Analysis Branch of the National Earth Satellite Service (NESS) on a continuous basis since November 1966. Based upon photo interpretation of 6 or 7 consecutive days of satellite imagery, the snow and ice boundaries are drawn on a 1:50,0000,000 polar stereographic projection of the Northern Hemisphere. Each of these charts for the period November 1966 through December 1980 were digitized at the University of Nebraska utilizing an 89 by 89 element box grid overlayed on the polar stereographic map. The grid which was utilized was compatible with the satellite-based Earth radiation budget atlas of Winston et al (1979). The true geographic area of each grid box varies with latitude as a result of the polar projection. However, this was taken into account mathematically, so that a true areal coverage of snow could be determined for a chart or for a region on a chart.