Sunday, October 25, 2009

Free Web-Enabled Landsat Data (WELD) Download

Free LandSat Image News Update! Dr. David P. Roy, from South Dakota State University, and company, have came up with "Web-enabled Landsat Data (WELD): Landsat ETM+ composited mosaics of the conterminous United States."

The Web-Enabled Landsat Data (WELD) project will improve the consistency and quality of Landsat Enhanced Thematic Mapper Plus (ETM+) data through a fusion with MODIS land products to systematically generate “seamless” consistent mosaicked ETM+ data sets with per-pixel quality assessment information and derived land cover characterization at monthly, seasonal, and annual time periods. The resulting high spatial resolution Landsat mosaic products will be generated for the conterminous USA and Alaska for a 7-year period and made freely available to the user community. The WELD project is funded by NASA’s Making Earth System Data Records for Use in Research Environments (MEaSUREs) program.

A preliminary WELD data set is available here, specifically, a 12-month annual composite of the conterminous U.S. generated from ETM+ orthorectified and terrain-corrected data acquired December 2007 to November 2008. In the future, other annual, seasonal, and monthly, mosaic data sets will be made available for evaluation by the user community.

These data are defined with 30m pixels in the Albers Equal Area projection with standard parallels 29.5°N, 45.5°N, latitude of origin 23°N, and central Meridian 96°W. The data are stored in Hierarchical Data Format (HDF) with HDF internal compression. HDF is a data file format designed by the National Center for Supercomputing Applications to assist users in the storage and manipulation of scientific data across diverse operating systems and machines. For example, it is used to store the standard MODIS products. Future product versions will have refined processing and content, most notably atmospheric correction, radiometric/BRDF normalization, improved cloud and ETM+ SLC-off gap-filling, and land-cover characterization.

The data are stored in tiles of 5000 x 5000 30m pixels. There are a total of 501 land tiles referenced using a two digit horizontal (HH) and vertical (VV) tile coordinate system reflected in the filename as conus.hHHvVV.2007dec-2008nov.v1.1.hdf. The image below illustrates the tile coordinate system.

A tile location tool is provided to locate pixels and tiles for given longitude and latitude coordinates. The tool is available for computers running Unix/Linux operating systems, the C source code and installation instructions can be downloaded HERE. A web-interface version of this tool will be available shortly. In addition, for each tile there is a static conus.hHHvVV.coordinates.hdf file that contains the geographic latitude and longitude for the center of each 30m pixel (datum WGS84).

The tile data are available from this EROS web site HERE.

Note that each mosaic tile is typically 240MB and the total size of all 501 mosaic tiles is 107GB, and that each static geographic latitude and longitude file is typically 110 MB and the total size of all 501 tiles is 53GB.

Update: October 20, 2010 - Free WELD Data - Latest Version Now Available

Data citation
Roy, D.P., Ju, J., Kline, K., Scaramuzza, P.L., Kovalskyy, V., Hansen, M.C., Loveland, T.R., Vermote, E.F., Zhang, C., 2010, Web-enabled Landsat Data (WELD): Landsat ETM+ Composited Mosaics of the Conterminous United States, Remote Sensing of Environment, 114: 35-49. Download the PDF.


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