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NSIDC Archived Data Format Instructions

File Layout

The monthly files, named SNODAS_YYYYMM, are .tar archives that contain a series of the following daily files.

The daily files, named SNODAS_YYYYMMDD, are .tar archives that contain a series of smaller .tar.gz files that correspond to different physical elements.

us_ssmv01025SlL00T0024TTNATS2006010105DP001.tar.gz -- Non-snow precipitation, 24-hour total
us_ssmv01025SlL01T0024TTNATS2006010105DP001.tar.gz -- Snow precipitation, 24-hour total
us_ssmv11034tS__T0001TTNATS2006010105HP001.tar.gz -- Modeled snow water equivalent
us_ssmv11036tS__T0001TTNATS2006010105HP001.tar.gz -- Modeled snow depth
us_ssmv11038wS__A0024TTNATS2006010105DP001.tar.gz -- Modeled snowpack average temperature, 24-hour average
us_ssmv11039lL00T0024TTNATS2006010105DP000.tar.gz -- Modeled blowing snow sublimation rate, 24-hour total
us_ssmv11044bS__T0024TTNATS2006010105DP000.tar.gz -- Modeled melt rate, 24-hour total
us_ssmv11050lL00T0024TTNATS2006010105DP000.tar.gz -- Modeled snowpack sublimation rate, 24-hour total

Each of these files, in turn, can be uncompressed into two separate files, a text header file with a .txt suffix, and a binary raster file containing "big-endian" values with a .dat suffix.


Decompressing Instructions

Decompressing instructions by operating system:
Unix/Linux/Mac -- On the command line:
tar xvf {daily or monthly file}
and then
tar -xvzf {extracted physical element file}
Mac -- In addition to the command-line option above, you can also use an interactive program such as Stuffit Expander.
Windows -- Interactive programs such as 7-zip, Stuffit Expander, or WinZip should work.
If you use WinZip, make sure the "TAR file smart CR/LF conversion" option in Options -> Configuration -> Miscellaneous is unchecked.

Bringing Binary Raster Files into ArcMap

  1. First, the .dat file has to be renamed to have a .bil suffix.

    Copy or Rename "us_ssmv01025SlL00T0024TTNATS2006010105DP001.dat" to "us_ssmv01025SlL00T0024TTNATS2006010105DP001_new.bil"
  2. Second, create a text header file for the .bil file in a text editor with the following contents:

    byteorder M
    layout bil
    nbands 1
    nbits 16
    ncols 6935
    nrows 3351
    ulxmap -124.729583333333
    ulymap 52.8704166666666
    xdim 0.00833333333333333
    ydim 0.00833333333333333
    The corresponding values can be
    found in the following fields 
    in the .txt file:
    Number of columns: 
    Number of rows: 
    Benchmark x-axis coordinate:
    Benchmark y-axis coordinate:
    X-axis resolution:
    Y-axis resolution:

    Name this file the same as the .bil file, except with a .hdr file suffix.
    (In the example above, the new header file name would be "us_ssmv01025SlL00T0024TTNATS2006010105DP001_new.hdr".)

  3. Open ArcMap and choose File -> Add Data. Locate the location of the new .bil (and the not shown .hdr) file, and click on the file to add the data. You will see a range of values for the raster. The value -9999 is the "no data value". You may also see 55537 instead, which is due to Arc treating the file as "unsigned" (mapping negative values to high positive values) rather than properly positive/negative signed.

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Page last modified: Oct 27, 2022 - cloud
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