Historical and seasonal Landsat data: WELD Resource
The Web-enabled Landsat Data (WELD) project generates 30-meter composites of Landsat 7 Enhanced Thematic Mapper Plus (ETM+) terrain corrected (Level 1T) mosaics at weekly, monthly, seasonal and annual periods for the conterminous United States (CONUS) and Alaska. These mosaics provide consistent data that can be used to derive land cover as well as geophysical and biophysical products for regional assessment of surface dynamics and to study Earth system functioning.
A collaboration between the United States Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center and academic partner South Dakota State University Geographic Information Science Center of Excellence, this is an excellent resource for all who seek to compare land use through time and through seasonal variation using Landsat data in the continental USA and in Alaska. The WELD documentation site describes the WELD products on the site, known issues, and future plans.
WELD products are available as custom GeoTiff subsets via a new interactive web ordering system and as tiled HDF products via FTP. I found the site fairly intuitive, simple, and straightforward to use. Its products are directly importable into GIS software and hence it provides much more than visualizations, but rather, products useful to the GIS analyst. The “good news, bad news” is that the GIS data user is confronted with an array of Landsat sites from which they may obtain data. Each has its own interface and formats, but the situation is still far better than 10 years ago when nearly all of it was either for fee or difficult to obtain. Because it is not well linked to other sites, the WELD site is difficult to “stumble across” unless the data user is familiar with the acronym. However, it is well worth a visit as it is one of the most intuitive and resource-rich.