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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.
| Example: |
| 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 .Hdr suffix, and a binary raster
file with a .dat suffix.
- Example:
- us_ssmv01025SlL00T0024TTNATS2006010105DP001.Hdr
- us_ssmv01025SlL00T0024TTNATS2006010105DP001.dat
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
-
First, the .dat file has to be renamed to have a .bil suffix.
- Example:
- Copy or Rename "us_ssmv01025SlL00T0024TTNATS2006010105DP001.dat" to
"us_ssmv01025SlL00T0024TTNATS2006010105DP001_new.bil"
-
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 .Hdr 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".)
NOTE: Arc may get confused if the new header suffixed with .hdr and the
old header suffixed with .Hdr have the name basename in the same directory.
-
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 65535 is the "no data value".
|
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