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NSIDC has created monthly ocean masks for users who want to know the maximum sea ice extent during a particular month, or who wish to mask out false sea ice concentrations caused by weather effects and/or land contamination. The ocean masks are very similar to the Monthly Climatology of Sea Ice Concentrations from NSIDC. But, the ocean mask is a binary indicator (ice/no ice), whereas the monthly means give the climatological percentage of monthly mean sea ice concentration (0-100%).
The ocean masks were derived for each month from the Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data using the NASA Team sea ice algorithm. The first processing step involved averaging the sea ice concentrations for each series of months throughout the time series, November 1978 through December 2003, to create 12 monthly ice concentration climatologies for the entire series. To derive the monthly ocean masks, individual pixels containing any fraction of ice in these monthly-averaged sea ice concentrations were flagged as ice-covered, and all other non-land pixels were flagged as open water.
Ocean mask data are in flat, binary files with an image size of 304 x 448 pixels (bytes) for Arctic data, and 316 x 332 pixels (bytes) for Antarctic data. Ocean mask files exist for each month of the time series. An example of the file naming convention is oceanmask.apr.1979-2007.n (or .s) for the April Northern Hemisphere ocean mask, spanning the time series (1979 through 2007). Pixel values, coded for water, ice, coast, land or lakes, are indicated below:
0 = water
1 = ice
2 = coast
3 = land
4 = lakes
PNG images of maximum ice extent are also available for both the Arctic and Antarctica, and are derived from the ocean masks. If ice was present in any of the twelve monthly ocean masks, the corresponding pixels were classified as ice in the final ice extent image. Data files for the maximum ice extent grids are in flat one-byte binary format (304 x 448 pixels for the Arctic, and 316 x 332 pixels for the Antarctic region). The file naming convention is max_extent_mask.1979-2003.n (or .s). Corresponding PNG images are also provided.
| Data are available via FTP |
