On a warm July day in 1972, NASA launched a new Earth-imaging satellite called the Earth Resources Technology Satellite. “ERTS” was the first satellite of what later became NASA and the US Geological Survey’s Landsat program, an ambitious effort with a vision to document the entire Earth from space. The first Landsat was so successful that it led to a series of satellites that produced the longest continuous record of the Earth’s surface from the perspective of the eye of space – which continues to grow today, 50 years later.
“The first Landsats revolutionized the way we observed Earth from space,” said Jim Irons, director emeritus of the Earth Sciences Division at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.Since its debut, Landsat has accumulated more than 10 million images. These images, also called scenes, show current images of the land and coastline, but are paired with images from years past and also reveal changes over time – slowly disappearing glaciers or urban spaces sprawling across the landscape.
These scenes and time series have countless applications around the world: Hydrologists use them to track changes in rivers; environmentalists use them to determine the extent of deforestation; farmers and agricultural organizations use them to analyze crop health.During Landsat’s five decades, eight different Landsat satellites have orbited the planet. Currently, three continue to collect global observations from space: Landsat 7, 8, and 9. (Landsat 6 was lost shortly after launch.) Landsat 9, the newest of the group, entered orbit in the fall of 2021. While Landsat 9 shares similarities with its predecessors, Landsat satellite design has evolved immensely since the program’s inception.
The first two Landsats could see in four spectral bands, or wavelengths, of light: visible light in red and green, and two near-infrared bands. Near-infrared radiation allowed satellites to distinguish vegetation from other land covers and assess plant health, while visible wavelengths distinguished bright surfaces such as snow, deserts and clouds from dark surfaces such as water. Each scene covered a roughly square area about 115 miles on a side.
Data from the first Landsats broadcast to Earth was recorded on magnetic tapes, the same basic technology as music cassettes—but much larger: The bulky wideband video recorders that flew on the first three Landsats each had 1,800 feet of tape and weighed 76 pounds apiece.
From this data, the researchers generated and printed photographic images. These photos provided a general view of the area from space, but the real power of the data came after computer algorithms helped scientists and resource managers more effectively identify the land cover categories they represented. Printers churned out paper maps with combinations of letters, numbers, and symbols, where each character represented a category of land cover, such as arable land or forest.
“You’d get out colored pencils or magic markers and color different characters, each with their own color,” Irons said. “That would give you an early version of a color-coded land cover map.” Goddard has been NASA’s home for Landsat since the program’s inception. Irons served as Deputy Project Scientist on Landsat 7 and Project Scientist on Landsat 8, helping to further shape the program and playing a key role in the development of the satellites. During his 43 years working with Landsat, he watched the satellites grow into what they are today.
Landsat data in the 1980s and 1990s was critical to many projects, such as understanding the extent of rainforest tree loss, Irons said. Similarly, Chris Neigh, a Landsat 9 project scientist at Goddard, is using time series to track the slow northward creep of boreal forests as trees gradually move closer to the pole in response to global warming. The long pedigree of Landsat data is essential for this kind of research, Neigh added: there are only a few other records to refer to, and none as complete.
2000: Free access to the Landsat archive
After the failed launch of Landsat 6, Landsat 7 successfully launched in 1999, equipped with improved instruments and roughly twice the resolution of its predecessors. Between the launches of Landsat 7 and Landsat 8, NASA spent seven years considering and trying to decide how to move forward with the program before starting another seven-year process of building and launching the next satellite.
At that time, management of imagery from commercial providers reverted to the USGS, which made the entire Landsat archive available in 2008. Image requests have skyrocketed. In 2020, Landsat downloads exceeded 100 million scenes and this number is still growing.As Landsat continues to transform, so do the people and projects that use it: The United States Department of Agriculture relies on Landsat to guide farmers in irrigation and soil management; climatologists watch glaciers retreat as temperatures rise; in the drought-stricken West, water managers are monitoring reservoir levels.
Landsat’s next adventure
With a community of data users that continues to grow, scientists and engineers are already looking forward to the next mission. NASA and USGS are developing options for the next iteration of Landsat, currently called Landsat Next. Landsat’s eyes in space have provided new opportunities to understand our changing planet, but the simple awe of seeing Earth is sometimes forgotten, Irons said. “We can’t all be astronauts,” Irons said. “But by looking at Landsat images, we can understand what the Earth would look like if we were orbiting the Earth in space.”
For more read: https://www.nasa.gov/feature/goddard/2022/landsat-legacy-nasa-usgs-program-observing-earth-from-space-turns-50
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