Knowledge Base

How do I import SNODAS data into ArcGIS?

Follow the steps below, which are also linked to from the SNODAS user guide. These steps will work for all 8 SNODAS variables using 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. To account for this shift, you need to modify the spatial bounds in the masked header file depending on your period of interest.

For data processed before Oct 01 2013 the spatial bounds for the masked header file are:
ulxmap  -124.73375000
ulymap  52.87458333
For data processed after Oct 01 2013 the spatial bounds for the masked header file are:
ulxmap  -124.73333333
ulymap  52.87500000

This example imports snow depth data from March 1, 2015.

filename= us_ssmv01025SlL00T0024TTNATS2015030105DP001.dat


1. Create the following header file and give it the same name as "filename" but with a .hdr extentsion. Remember to place in the same directory as "filename.dat".

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 -124.73333333
ulymap 52.87500000
xdim 0.00833333333
ydim 0.00833333333 

For unmasked data (files beginning with 'zz'):

nrows 4096
ncols 8192
nbands 1
nbits 16
pixeltype signedint
byteorder M
layout dat
ulxmap -130.517083333328
ulymap 58.2329166666644
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 November 2018

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