Landsat Orthorectified TM: The average acquisition date for the 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.

Systematic Correction includes both radiometric and geometric correction. The scene will be rotated, aligned, and georeferenced to a user-defined map projection. Absolute geometric accuracy of the systematically corrected TM product can vary, depending upon the accuracy of the predicted ephemeris that is used for processing. Users should be aware that subsequent image geocorrection and/or co-registration to known ground control points (GCPs) may be necessary with a TM product.

Terrain Correction includes radiometric, geometric, and precision correction, as well as the use of a digital elevation model (DEM) to correct parallax error due to local topographic relief. For locations outside the U.S., accuracy of the terrain-corrected product will depend upon the availability of local ground control points (GCPs), as well as the resolution of the best available DEM.

Las Vegas, Nevada 1964, 1972, 1986, 1992 - Land Cover Mapping and Change Detection http://earthshots.usgs.gov/LasVegas/LasVegas

Iraq-Kuwait 1972, 1990, 1991, 1997 - Impacts of the defenses from the Iran-Iraq War, oil fires from the 1991 Gulf War, and waterworks inside Iraq Draining of the Iraqui marshes, Irrigation in Mesopotamia, Trenching along the border, Spilling and burning in Kuwait http://earthshots.usgs.gov/Iraq/Iraq