On a warm July day in 1972, NASA launched a new Earth imaging satellite called the Earth Resources Technology Satellite (ERTS). ERTS was the first satellite of what would become NASA’s Landsat program and the US Geological Survey (USGS), an ambitious effort with a vision to document the entire Earth, the Earth from space. The first Landsat was so successful that it led to a series of satellites that created the longest continuous record of the Earth’s surface from space; And that continues to grow to this day, 50 years later.
“Landsat’s first spacecraft revolutionized the way we observe Earth from space,” said Jim Irons, director emeritus of Earth Sciences at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Since its inception, Landsat has collected more than 10 million images. Also called scenes, these images show current snapshots of soil and coastlines, but are combined with images from past years and also reveal changes over time: slowly disappearing glaciers or urban spaces stretching across the landscape.
These scenes and timelines have countless applications around the world: hydrologists use them to keep track of how rivers are changing; Environmentalists use them to determine the extent of deforestation; Farmers and agricultural organizations use them to analyze the health of crops.
During the five decades of the Landsat program in existence, eight different Landsat satellites have orbited the planet. Currently, three groups 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 a facet Similar to its predecessors, the design of the Landsat satellite has evolved significantly since the beginning of the program.
At first
The first two Landsats could see four spectral bands, or wavelengths of light: visible light in red and green, and two bands in the near infrared. El infrarrojo cercano permitía a los satélites distinguir la vegetación de otras cubiertas terrestres y evaluar la salud de las plantas, mientras que las longitudes de onda visibles diferenciaban las superficies brillantes, como desierlas nieves comoes, los nieves como water. Each scene covered an approximate square area of about 185 kilometers (115 miles) on one side.
The Earth Resources Technology Satellite (ERTS, later renamed Landsat 1) was launched aboard a Delta 900 aircraft from Vandenberg Air Force Base on July 23, 1972.
Credit: NASA image provided by the Landsat Science Team
Data from the first Landsat sent back to Earth was recorded on magnetic tape, using the same basic technology as music cassette tapes, but much larger: the massive broadband video recorders that traveled aboard the first three Landsats each had approximately 1,800 feet (550 m) of tape and weighs 76 lbs (34.5 kg) each.
From this data, scientists create and print photographs. These images gave an overview of an area of space, but the real power of the data came after computer algorithms helped scientists and resource managers more efficiently determine which land cover classes they represented. Printers spit out paper maps with combinations of letters, numbers, and symbols, with each feature representing a category of land cover, such as farmland or a forest.
“Colored pencils or markers were used to color the different themes, each with its own color,” Irons said. “This gave an early version of the color-coded land cover map.”
The Goddard Center has been the home of NASA Landsat since the beginning of the program. Irons served as deputy project scientist on Landsat 7 and project scientist on Landsat 8, helping to shape the program and playing a critical role in satellite development. In his 43 years of working with Landsat, he’s seen satellites grow into what they are today.
Irons said that Landsat data in the 1980s and 1990s was crucial to many projects, such as understanding the extent of tree loss in tropical rainforests. Similarly, Chris Neigh, a Landsat 9 project scientist at Goddard, uses a time series to see the slow progression northward of boreal forests, as trees gradually move toward the pole in response to global warming. Nye added that the long history of Landsat data is essential for this type of research: there are few additional records to reference, and none of them are complete.
The first fully functional Landsat image of Dallas, Texas, was taken on July 25, 1972, beginning a 40-year career when the first satellite was known as the Earth Resources Technology Satellite (ERTS).
Credits: NASA Earth Observatory
The first decade of the twenty-first century: free access to the Landsat archive
After the unsuccessful launch of Landsat 6, Landsat 7 took off successfully in 1999, with improved hardware and almost twice the accuracy of its predecessors. NASA debated for seven years between the launch of the Landsat 7 and Landsat 8 satellites, trying to determine how to move forward with the program before beginning another seven-year process of building and launching the next satellite.
At that point, image management was back out of the hands of commercial service providers to the USGS, which made all Landsat files freely available in 2008. Requests for images skyrocketed. Landsat photo downloads exceeded 100 million views in 2020, and that number continues to grow.
As Landsat continues to transform, so are the people and projects that use it: The USDA uses Landsat to guide farmers on irrigation and land management practices; Climate scientists watch glaciers retreat as temperatures rise; In the drought-stricken west, water managers monitor reservoir levels.
Next Landsat adventure
With the data user community that continues to grow, scientists and engineers are already looking forward to the next task. NASA and the USGS are developing options for the next version of Landsat, which is currently called Landsat Next.
Irons said Landsat’s eyes in space have given us new opportunities to understand our changing planet, but the simple wonder of seeing Earth is sometimes forgotten.
“We can’t all be astronauts,” Irons said. “But if we look at Landsat images, we can understand what the Earth would be like if we were orbiting from space.”
By Judd Coleman
Goddard Space Flight Center in Greenbelt, Maryland
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