Landsat TM Mosaic Data
The GeoCover-Ortho program, sponsored under NASA’s Scientific Data Buy program, has been designed to create a geodetically accurate digital database of Landsat TM (circa 1990) and MSS multispectral (1972–1979) images covering the entire Earth’s land mass. The EarthSat Corporation is producing these data for NASA. These image mosaics are false-color images created from 12 to 15 Landsat TM images using bands 7, 4, and 2 for the Red, Green, and Blue layers. The raster cell resolution is 28.5 meters and the horizontal positional accuracy is less than 50 meters.
The scenes are segmented into tiles of approximately 250,000 square kilometers. Each tile covers five degrees of latitude in a UTM zone, which is 6 degrees of longitude. The scenes are identified by Universal Transverse Mercator (UTM) zone and minimum latitude of the tile. For example, Connecticut would be tile N-18-40 and Buenos Aires, Argentina would be tile S-21-30. You can learn more about the UTM projection in the CEO User's Guide.
These mosaic images are in MrSid® format and can be used directly in ArcView, ArcGIS, ERDAS Imagine, or the free MrSid Viewer available from LizardTech. Data are in the WGS84 datum and UTM projection. These tiles are very useful to geo-reference images where there are no readily available ground control points, or to produce quick maps of large regions.
While the CEO has many mosaic tiles available in the lab, you can select and download additional data from the NASA web site
After zooming in to the tile you are interested in, click on the radio button "Select EarthSat MrSid Image to View". After clicking on the tile once more you will be brought to a page that allows you to view the mosaic and download the file. It is approximately 50 MB. The file will be in a "tar" format that can be unzipped using most Unix or PC unzip utilities such as WinZip. To view the image in ArcView you must activate the MrSid extension and load the ".sid" file as an image feature. These images can also be used in the Image Analyst extension to ArcView to geo-reference other images and aerial photos.
We have downloaded many mosaic tiles of approximately 50 MB each from the above mentioned NASA web site. The tiles are archived on CDs in the lab. As mentioned above, each tile is identified by the hemisphere, N (north) or S (south) and UTM zone (range from 01 to 60), and the minimum lattitude of the five degree span of the tile.