Snow/ice monthly stataistics and climatology for Northern Hemisphere
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The product includes monthly snow/ice statistics (frequency of occurence) and snow/ice
occurence climatology for Northern Hemisphere at 1 degree spatial resolution. The dataset covers the time period strating January 2000. Currently the last month processed is December 2006.
The dataset is updated routinely on 10th day of every month

Monthly snow and ice maps and climatology are derived from daily snow and cover charts
produced at NOAA/NESDIS within Interactive Multisensor Snow and Ice Mapping System (IMS)
Original IMS snow/ice charts are generated on a 1024x1024 grid in polar projection 
at a nominal resolution of about 24 km (see http://www.ssd.noaa.gov/PS/SNOW/index.html)
The monthly snow and ice frequency of occurence for 1 degree grid cells is calculated as 
an average of all daily fractions of snow and ice for a given month. The monthly climatology 
was obtained through averaging monthly data for individual years.

Snow and Ice cover statistics (frequency of occurrence) are calculated if the grid cell has at least some land and some water, respectively. Otherwise the pixel is label "undetermined"

Data files are 1-byte binary with 360 pixels per line and 90 lines. The projection is 
latitude-longitude with the upper left corner of the first pixel of the first line 
positioned at 90N 180W.

The naming convention:

ims_snow_stat_mm_yyyy is the monthly snow cover statistsics. "mm" is a two digit month number, and "yyy" is a four-digit year
ims_ice__stat_mm_yyyy is the monthly ice cover statistsics. "mm" is a two digit month number, and "yyy" is a four-digit year

ims_snow_clim_mm      snow occurence climatology (average of monthly values for individual years) for month "mm"
ims_ice _clim_mm      ice occurence climatology (average of monthly values for individual years) for month "mm"

The meaning of byte values:

Snow Cover

0     :   snow free land surface
1-100 :   snow frequency of occurence (from 1 to 100%)
250   :   undetermined (ocean or area outside the domain of IMS)

Ice Cover

0    :  ice free sea surface
1-100:  sea ice frequency of occurence (from 1 to 100%)
250  :  undetermined (land or area outside the domain of IMS)