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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 .txt suffix, and a binary raster
file containing "big-endian" values with a .dat suffix.
- Example:
- us_ssmv01025SlL00T0024TTNATS2006010105DP001.txt
- 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 .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".)
-
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.
|