Landsat 4

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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.

One project from researchers at the USGS Earth Resources Observation and Science (EROS) Center, for example, has mapped water annual use from 1982-present across the entirety of the Rio Grande Basin—a task that would be impossible without the 40-year trove of TM data made available through the Landsat archive. 

Visit the full Landsat 4 page on the Landsat Missions website.