Version 1.0 Release 06/13/2013
The key features of SNODA_SWE.py are described below. Please refer to SNODAS_SWE.py User Guide for using the tool.
Capable of unpacking 3 different compressed files formats of SNODAS data. See the Data File Formats of SNODAS Data section for more information of the input data format.
Performs ArcPy's Geoprocessing functions to convert the SWE source .dat and .hdr files into raster GIS dataset (in ERDAS .img format). The specific geoprocessing tasks involved are:
Convert signed integer format that is not supported in GRID format to unsigned integer format.
Define the projection of the source data. The source data is in WGS 84 Geographic Coordinate System.
Reprojects the data from WGS 84 to NAD 83, USA Contiguous Albers Equal Area Conic USGS version.
Converts the raster to .img format.
Allows command line or interactive execution of the script. Please see the User Guide for script execution instructions.
Capable of creating a backup copy of the source data for future use.
Three source data formats that can be used as the input to SNODAS_SWE.py. Files in the final level decompressed format (in red) are used by ArcPy in the geoprocessing routines.
NSIDC ftp server URL is ftp://sidads.colorado.edu/. The masked SNODAS daily data can be found at
/DATASETS/NOAA/G02158/masked/. The download process can be done automatically with the ftpgetsnodas.py script. Users need to enter the year, month, and day on the prompts. See the SNODAS Tools User's Guide for instructions on using the ftpgetsnodas.py script.
The source SNODAS files are either pushed to USDA-NRCS and PSU CSAR ftp servers by NOHRSC or can be downloaded from the NSIDC ftp server. The acquired data are in compressed format and contain all eight SNODAS parameters, including solid precipitation, liquid precipitation, SWE, snow depth, snow pack average temperature, snow melt runoff, sublimation from snow pack, and sublimation of blowing snow. When decompressed, the source data contain binary .dat files that store the SNODAS data values and separate .hrd files for the header information. Such file structures need to be imported into a GIS software before they can be used for mapping or analytical purposes. The SNODAS_SWE.py Python script was developed to streamline the extraction and conversion of the SWE data for GIS. The output files of SNODAS_SWE.py are in GIS format (i.e., .img raster format) that can be used directly in GIS. The key features of SNODA_SWE.py include:
Capable of unpacking 3 different compressed files formats of SNODAS data. See Section 7.1. SNODAS Data Formats for more information of the input data format.
Performs ArcPy's Geoprocessing functions to convert the SWE source .dat and .hdr files into raster GIS dataset (in ERDAS Imagine .img format). The specific geoprocessing tasks involved are:
Converting signed integer format that is not supported in GRID format to unsigned integer format.
Defining the projection of the source data. The source data is in WGS 84 Geographic Coordinate System.
Reprojecting the data from WGS 84 to NAD 83, USA Contiguous Albers Equal Area Conic USGS version.
Converting the raster to .img format.
Allows command line batch execution or interactive execution of the script. Please see Section 7.2 for script execution instructions
Capable of creating a backup copy of the source data for future use.
The output .img files are in "USA Contiguous Albers Equal Area Conic USGS" projection. The spatial resolution is 923m by 923m. The unit of the integer cell value representing SWE is in millimeters. Users can divide the value by 1000 to get the SWE in meters.
Snow Data Assimilation System (SNODAS) Data Products at NSIDC (website)
SNODAS Tools Users Guide - SNODAS Tools Users Guide
Sample SNODAS tar files - Files are in CSAR SNODAS format. Click the View hyperlink to download the file.