The launch of Landsat 4 on July 16, 1982 represented a sea change for the program.
The satellite was the first to carry the Thematic Mapper ( TM ), a sensor that captured light reflected from the Earth’s surface across seven bands of the electromagnetic spectrum.
The TM had an improved resolution of 30 meters per pixel, about the size of an American baseball infield. Each subsequent Landsat has had the same resolution, and each pixel collected by each mission since has been corrected and calibrated to match both the geographic location of the plot of ground it represents and to align with every other pixel recorded at that location since the first Landsat launched.
That 40-year record of the Earth’s surface at 30 meters is what makes it possible for scientists to scan the spectral history of each pixel for short-term changes tied to seasons or weather events, and for long-lasting changes like conversion of grassland to cropland or cropland to urban land.