Knowledge Base

How do I import SNODAS data into ArcGIS?

Follow the steps below, which are also linked from the SNODAS user guide. These steps will work for all eight SNODAS variables in ArcGIS 10.0 or higher.

Before working through the rest of this tutorial, we would like to make you aware of a small spatial data shift that occurs on Oct 01, 2013 in the SNODAS period of record. On this date, the data provider, National Operational Hydrologic Remote Sensing Center (NOHRSC) slightly changed the center coordinates of the grid to align with an integer value of latitude and longitude. The resulting shift is minute, and on the order of 1/4 of a 1km grid cell. Therefore, please note that the date of the file(s) you wish to convert will determine which coordinates you will use in the header file for this tutorial. Example header files for data before and after 01 October 2013 are provided.


1. Create one of the following header files based on your dates and give it the same name as "filename" but with a .hdr extension. Remember to place in the same directory as "filename.dat".

For masked data processed before Oct 01 2013 (files beginning with 'us'):

nrows 3351
ncols 6935
nbands 1
nbits 16
pixeltype signedint
byteorder M
layout dat
ulxmap -124.72958333333334
ulymap 52.870416666666664
xdim 0.00833333333
ydim 0.00833333333

For masked data processed after Oct 01 2013 (files beginning with 'us'):

nrows 3351
ncols 6935
nbands 1
nbits 16
pixeltype signedint
byteorder M
layout dat
ulxmap -124.72916666666667
ulymap 52.87083333333334
xdim 0.00833333333
ydim 0.00833333333 

For unmasked data processed before Oct 01 2013 (files beginning with 'zz'):

nrows 4096
ncols 8192
nbands 1
nbits 16
pixeltype signedint
byteorder M
layout dat
ulxmap -130.51291666666665
ulymap 58.228750000000005
xdim 0.00833333333
ydim 0.00833333333 

For unmasked data processed after Oct 01 2013 (files beginning with 'zz'):

nrows 4096
ncols 8192
nbands 1
nbits 16
pixeltype signedint
byteorder M
layout dat
ulxmap -130.51250000000002
ulymap 58.229166666666664
xdim 0.00833333333
ydim 0.00833333333

2. Start ArcMap and click on the 'Add Data' icon located in the main toolbar. Browse, select, and open the .dat file to the map document. To add the file in a different format, follow step 3.

3. Start ArcMap and open ArcToolbox. Select Conversion Tools > To Raster > Raster to Other Format. The Raster to Other Format window will appear. In the Input Raster box, browse and select the .dat file. In the Output Workspace box, select the location to store the new data set. In the Output Format box, select the format you wish to create (e.g. TIFF, ENVI DAT, etc.). Click OK.

Last Updated October 2020