Each data file contains daily sea ice coverage data for a subregion of the Southern Hemisphere.   These data describe the percentage of ice cover for a given day on a ~9-km equal angle grid. This grid is the same as that used for the Level 3 smi (standard mapped image) chlorophyll files for SeaWiFS, or the 9 km sea surface temperature files available from the NOAA/NASA Pathfinder Project. Thus, it is useful for comparing with those data sets.

The original sea ice data is from the DMSP SSM/I F13 satellite sensor, obtained from the National Snow and Ice Data Center (NSIDC) at the EOSDIS NSIDC Distributed Active Archive Center, at the University of Colorado at Boulder, (http://www-nsidc.colorado.edu/index.html or ftp sidads.colorado.edu in the directory /pub/DATASETS/SSMI/).

The data presented here were derived from the DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations (NASA Team Algorithm), which are distributed on a polar stereographic projection with a spatial resolution of 25 x 25 km. We have remapped this data to our ~9 km equal-angle grid to ease comparison with the other satellite data sets. These data should not be used obtain the percentage ice cover at a particular location. For that pupose we recommend that users obtain the original data and free software for extraction of concentration at individual locations from the NSIDC.

In each daily file, the values from 0 - 100 are the percent ice cover for that day. Missing data are flagged with values of 157, land areas are set equal to 220.

The filenames contain either the year, month, and day in YYMMDD format or the year and week in YYWW format, where week 1 is Jan 1 - 7.

The data are available in two formats:

• binary
• ASCII

Binary data

The binary data files can be downloaded from pages with the corresponding monthly images (for region 1) or from the data page.   Each file consists of a single byte array comprised of unsigned, 8-bit integers .  The auxiliary file for region 1, icescalebar (10 kb), contains a byte array (160, 60) that contains a scale bar for displaying the ice coverage.

Note that for region 1, data(0,0) corresponds to data(0,113) on the global 9 km equal angle grids used for SeaWIFS and the SST data (i.e. the data arrays are offset by 113 rows).

To load the data in IDL programming language (for region 1):

data=bytarr(4096,571)
openr,99,filename
readu,99,data
close,99

To calculate the center location of any gridpoint, the following IDL routine can be used (for region 1):

PRO latlon, x, y, lat, lon
; negative values indicate West, all lat in degrees South (positive)
lon=float((x*0.08789)-179.95606)
lat=float(80.0245-(y*0.08789))
print,"lon= ",lon
print,"lat= ",lat
RETURN
END

To calculate the gridpoint of a lat/lon location (for region 1), use:

PRO xylatlong, x,y, lat, lon
; Converts lat, lon to x,y coord in Southern Ocean Files
; Negative numbers indicate western long.
IF (lon LT 0) then begin
x=fix((179.95606+lon)/0.08789)
endif else x=fix((179.95606+lon)/0.08789)
y=fix((80.0245-lat)/0.08789)

ASCII data

The data are also available in ascii format as arrays of sea ice coverage values (%) for each day.  These files can also be downloaded from pages with the corresponding monthly images (for region 1) or from the data page. Two separate ascii files (icelat.dat and icelon.dat) found in icelatlon.zip contain the corresponding latitude (^oS) and longitude (^oE) arrays, respectively.  Each daily, uncompressed data file is approximately 37 Mb in size.

Documentation by J. Keith Moore, Oregon State University.
Webpage by Jasmine S. Bartlett, Oregon State University.