Directory contains global maps of snow cover yearly duration derived from GMASI V3 reprocessed daily maps of snow and ice cover
The dataset starts in 1988
As of January 2023 the dataset is updated up to the year 2022 

Snow cover duration in every grid cell equals to the number of days when the grid cell was identified as snow-covered 
by GMASI. Yearly snow cover duration has been calculated for a calendar year, from Januay 1 to December 31 (not for the hydrological year)

Multiyear mean snow cover duration is calculated by averaging yearly snow cover duration for all years except years 
1993 and 1994. A very late overpass time of NOAA satellite in these years period resulted in a substantial overestimate 
of the snow cover extent in the Southern Hemisphere. To a lesser extent this issue also affected the Northern Hemisphere 
snow and ice cover retrievals 

When calculating the multiyear mean snow cover duration for leap years pixels with the snow duration of 365 and 366 days 
were assigned the snow duration of 365 days.

The Antarctic continent is assumed snow covered all year round.

Map features
Projection:       Geographical
Grid step : 0.04 by 0.04 degree 
Grid size : 9000 by 4500
Upper left corner of the upper left grid cell: 90N, 180W
Orientation: North to South and West to East
Data format: 2-byte integer

Data values
0 to 365: snow duration in days
1000: water

Binary data files are in the data directory
Files are zipped with Linux compress command

Corresponding reduced resolution .png images are in the png directory