The Landsat GeoCover collection of global imagery was merged into mosaics by the
Earth Satellite Company (now MDA Federal). The result was a series of tiled imagery
that is easier to wield than individual scenes, especially since they cover larger
areas than the originals. The great detail in these mosaic scenes, however, makes
them large in storage size, so the Mr.Sid file format, which includes compression
operations, was chosen for output. While GeoCover itself is available in three
epochs of 1975, 1990 and 2000, only the later two epochs were made into mosaics.
For further details, please check out the official