Landsat ETM+, TM, and MSS data are available from USGS for free. Base data page leads on to:
Full description from USGS page states:
The Tri-Decadal Global Landsat Orthorectified data collection consists of a global set of high-quality, relatively cloud-free orthorectified MSS, TM and ETM+ imagery from Landsats 1-5 and 7. This dataset was selected and generated through NASA's Commercial Remote Sensing Program, as part of a cooperative effort between NASA and the commercial remote sensing community to provide users with access to quality-screened, high-resolution satellite images with global coverage over the Earth's land masses. The data collection was compiled via NASA contract with Earth Satellite Corporation (Rockville, MD) in association with NASA's Scientific Data Purchase program.
The Tri-Decadal Global Landsat Orthorectified data collection consists of approximately 7,500 MSS (Landsat 1-5) images, 7,461 TM (Landsat 4-5) images and approximately 8,500 ETM+ (Landsat 7) images, which were selected to provide three full sets of global coverage over an approximate 25-year interval (circa 1975, circa 1990 and circa 2000). All selected images were either cloud-free or contained minimal cloud cover. In addition, only images with a high quality ranking in regards to the possible presence of errors such as missing scans or saturated bands were selected.
The following data products are available from the Tri-Decadal Global Landsat Orthorectified data collection:
Tri-Decadal Global Landsat Orthorectified MSS
The average acquisition date for the Tri-Decadal Global Landsat Orthorectified MSS data is in the mid-1970s relative to a 1990 acquisition baseline for the Tri-Decadal Global Landsat Orthorectified TM images. +/-3 years of the 1990 baseline). However, individual scenes range from 1972 to 1987. These Landsat data were orthorectified, using geodetic and elevation control data to correct for positional accuracy and relief displacement. Large blocks of Landsat data were adjusted through a patented procedure that uses pixel correlation to acquire tie-points within the overlap area between adjacent Landsat images.
Tri-Decadal Global Landsat Orthorectified TM
The average acquisition date for the Tri-Decadal Global Landsat Orthorectified TM data is 1990 (+/- 3 years). However, individual scenes range from 1985 to 1996. These Landsat data have been orthorectified, using geodetic and elevation control data to correct for positional accuracy and relief displacement. Large blocks of Landsat data were adjusted through a patented procedure using pixel correlation to acquire tie-points within the overlap area between adjacent Landsat images.
Tri-Decadal Global Landsat Orthorectified ETM+
The average acquisition date for the Tri-Decadal Global Landsat Orthorectified ETM+ data is 2000 (+/- 1 year). All scenes were acquired between 1999 and 2001. These data have been orthorectified for co-registration with the earlier (circa 1990) Landsat TM coverage.
Tri-Decadal Global Landsat Orthorectified ETM+ Pan-sharpened
These data products consist of pan-sharpened versions of the ETM+ scenes above. The pan-sharpening process involved a resolution merging process, which allows the fusion of the higher-resolution panchromatic band (8) with selected lower-resolution multispectral bands (7,4,2) to create a higher-resolution ("pan-sharpened") color image.
Systematic Correction (Level 1G) (SLC-on and SLC-off)
The Level 1G (L1G) data product provides systematic radiometric and geometric accuracy, which is derived from data collected by the sensor and spacecraft. The scenes were rotated, aligned, and georeferenced to UTM map projection. Geometric accuracy of the systematically corrected product should be within 250 meters (1 sigma) for low-relief areas at sea level. The SLC-off product includes the original data gaps. Duplicated pixels have been replaced with null values (zero-fill); therefore the image contains alternating stripes of missing data. A scan gap mask is included with the final product. Please click here for more information on SLC-off L1G data.
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Retrieved 12:16, May 22, 2013 (UTC).
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