Knowledge Base

How to import Global Monthly EASE-Grid SWE data products into ArcGIS

The global, monthly SWE EASE-Grid products can be found at the following link:

http://nsidc.org/data/nsidc-0271.html

1. Follow the instructions for importing priginal EASE-Grid data from the Importing Passive Microwave EASE-Grid Data into GIS webpage. Unlike the DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures or Nimbus-7 SMMR Pathfinder Daily EASE-Grid Brightness Temperatures data files, the SWE data won’t need to be unzipped when downloaded. 
Note: Make sure that when using a SWE product from the Northern Hemisphere, you also use a header for the Northern Hemisphere and you rename this header file to match the data file.

2. Since monthly EASE-Grid SWE data are 16-bit, signed integer files, the data need to be formatted that way. In ArcGIS open up the ArcToolBox →  Spatial Analyst Tools → Map Algebra → Multi Output Map Algebra. In the new input box, type the following command in the Map Algebra Expression box:

filename = con(filename >= 32768, filename - 65536, filename)

Filename = the new ESRI compatible grid format generated after completing Step 1.


Click OK.

Note: Make sure that the syntax for the expression is followed exactly how it is displayed here (i.e. with a space between numbers and/or the file name), otherwise the conversion won’t work or be incorrect.

***New for ArcMap 10***
You do not need to do the map algebra step any longer.  Modify the header file to include "pixeltype signedint" (See the Southern Hemisphere 25km header below for an example) and the data will be formatted correctly. 

Southern Hemisphere 25 km Header file for ArcMap 10+:

nrows 721
ncols 721
nbands 1
nbits 16
pixeltype signedint
layout bsq
byteorder I
ulxmap -9024309
ulymap 9024309
xdim 25067.525
ydim 25067.525