The sustainability requirement of present-day forest ecosystem management necessitates
resource data that are accurate and continuously updated. Until vertical aerial photos became available
in the 1930's, forest managers were totally dependent upon resource information obtained on the ground.
Aerial photography immediately proved to be a valuable asset, greatly facilitating the acquisition of much
of the required knowledge. The launch of Landsat-1 in 1972 marked the beginning of satellite remote
sensing for renewable resources applications. Because of their synoptic and repetitive data acquisition
capabilities, satellite-based sensors hold the potential to detect, identify, and map canopy changes that are
important to the forest ecosystem managers. Aldrich predicted in 1975 that "Even low-resolution data
from the Landsat MSS scanner, if combined and enhanced, will disclose 80 to 90% of the exchanges of
land use between forest and non-forest categories. In addition, such data will show 25 to 90% of the less
distinct disturbances in the forest, depending on the category.