Satellites capture an incredible variety of views of Earth. In this episode of Eyes on Earth, we talk with the three engineers at USGS EROS who started the USGS Earth As Art project. The Earth As Art origin story is an example of the initiative and creativity of EROS staff.
Landsat 7 Brought Jobs, Science, Art and Memories to USGS
We celebrate satellite's 25-plus years of contributions to EROS and the world
All Landsat satellites have been important to the USGS Earth Resources Observation and Science (EROS) Center. After all, storing and distributing Landsat data is the reason the EROS Center was created.
But as Landsat 7 completed its mission this year and we look back 25 years, the anticipation and excitement of the satellite’s launch in 1999 nearly rivaled the first Landsat’s launch in 1972.
Landsat 7 had been one key reason for an expansion of the EROS building and its workforce in the countryside near Sioux Falls, South Dakota. A new antenna for Landsat 7 had finally given EROS its status as a Landsat ground station. And the aging but persevering Landsat 5 would get some company capturing imagery of the Earth’s surface, providing a lot more data to the EROS archive.
Like many former and current employees, Brian Sauer was hired as a contractor to work at EROS. He started in 1998 as a self-described “database person” and soon transitioned to a systems engineer, all in preparation for systems needed at EROS that would support Landsat 7 data downlinking, processing and calibration.
“I remember all the welcoming messages,” Sauer said. “And there were all these complex technical things that were going on. It was an exciting time.”
Doug Daniels began working in project management at EROS in late 1997 on the USGS portion of the Landsat 7 ground system. He recalled one advantage new employees brought to EROS because of Landsat 7.
“It started growing skillsets at EROS that the center hadn’t previously seen. We had a ground station going in, so we had an influx of really intelligent and smart folks that were working on the ground networks and antennas and all the things that go along with the hardware and software pertaining to new satellite data,” Daniels said.
Besides the technical aspects of the Landsat 7 data flowing in after launch, scientists at EROS and around the globe imagined ways to use the data to learn more about the planet. Some of these EROS efforts included:
- Production of the definitive U.S. land cover resource National Land Cover Database.
- Development of an agriculturally significant evapotranspiration model, the Simplified Surface Energy Balance (SSEBop) model.
- Use of more than 1,000 Landsat 7 scenes for the collaborative Landsat Image Mosaic of Antarctica (LIMA) project, the first attempt at EROS to create a virtual mosaic (a series of interlinked files because a single massive file wasn’t possible).
- Initial creation of mosaics of each U.S. state compiled from Landsat 7 scenes.
A Launch of Hope
The launch of Landsat 7 on April 15, 1999, was memorable for many employees at EROS. For example, Daniels received an invitation to the launch at Vandenberg Air Force Base in southern California from NASA Goddard Space Flight Center, the base for Landsat flight operations.
In accepting the invitation, Daniels started a tradition with his three children. He brought his oldest daughter, age 4, to the launch of Landsat 7. His son attended the launch of Landsat 8 with him in 2013, and his youngest daughter accompanied him to Landsat 9’s launch in 2021. “It’s a unique opportunity that I’ve had,” he said.
Sauer and many other employees observed the Landsat 7 launch on a screen in the EROS auditorium. They were excited, of course, but also a little fearful, Sauer recalled.
“There was a lot relying on Landsat 7 here as a center,” he said. “It brought in our jobs.”
Sauer attributed the quiet in the auditorium at the time of launch to the knowledge that Landsat 7’s predecessor, Landsat 6, had failed to achieve orbit after its launch in 1993. “I think you could have heard a pin drop on a carpet floor in there,” he said.
Jon Christopherson recalled watching the launch in person with his wife and two young children from a golf course set up as a viewing area. It was far enough away from the launch pad that the roar of the soaring rocket took at least 30 seconds to hit them after they saw it rise, Christopherson estimated.
Christopherson had arrived at EROS in April 1997 to lead the newly formed Image Assessment System for the calibration and validation of Landsat imagery. He also brought along firsthand knowledge of Landsat 7. In his previous job at Hughes Santa Barbara Remote Sensing in California, he had worked on the Enhanced Thematic Mapper Plus (ETM+) instrument that would be attached to Landsat 7.
Christopherson remains in awe of rocket science—“just how dangerous and weird this is, to put your precious satellite on top of this 120-foot bomb and light it.”
Data Started Rolling In
Fortunately, the launch was a success. Christopherson then rushed back to EROS for the first imaging a few days later. He and a colleague watched on a computer screen at EROS as Landsat 7’s data stream, band by band, showed up like it was supposed to. They gave a thumbs up to employees huddled outside the room peering at them through the windows.
The first image, or first light, is the first time that light hits the detectors of the instrument and measures the surface of the Earth, Daniels explained. For Landsat 7, that first image was taken over eastern South Dakota, including Sioux Falls.
“That was fun,” Daniels said. “I think there was a little bit of a tribute that was being paid to the role that EROS played in the successful development, implementation and launch of Landsat 7.”
In addition to setting up its own ground station, EROS had worked with international partnering countries that had ground stations downlinking Landsat 7 data to ensure they followed standardized formats and methods compared to previous Landsat satellites, said Kristi Kline. She began working at EROS in connection with Landsat 7 in mid-1997 as part of the expansion’s new NASA Land Processes Distributed Active Archive Center (LP DAAC). “We tested them on a regular basis.”
Landsat 7 also had a suite of three gimbaled antennas onboard that could transmit data to three different ground stations at the same time—emphasizing the expanding international network and global interest in Landsat data, Daniels said. “Landsat 7 really made a substantial contribution to how Landsat data and science data was viewed on the international stage.”
Calibration—There’s a Science and an Art to It
Calibration is essential to ensuring the accuracy of satellite data. It involves comparing the accuracy of measurements from a satellite instrument with known reference plots on the land surface.
Landsat 7 represented a new era of calibration. After its launch—unlike its predecessors—Landsat 7 had calibration activity routinely performed at EROS by the Image Assessment System team, which then consisted of Christopherson, Pat Scaramuzza and Ron Hayes. The system assesses image quality and maintains calibration quality of the satellite and ETM+ instrument.
Sauer, in assisting with Landsat 7 systems, helped document the new Image Assessment System. “The highly calibrated data was really important to the community, important to the scientists, important to the applications that use the data. This was what started the gold standard in Landsat, and then it just carried over from mission to mission.”
The Image Assessment System work included daily checks of 10 randomly selected scenes per day, Scaramuzza recalled, to be sure there were no problems.
Occasionally, they came across an especially interesting or beautiful scene. For a year or more, Christopherson recalled, they hung printouts of these in the hallway, along with a brief description, for EROS co-workers to enjoy.
The team pondered how they could share the intriguing, colorful Landsat 7 images with people outside of EROS. Christopherson liked the idea of a coffee table book, but that wasn’t possible. And then Scaramuzza thought of an art show.
Landsat 7 in the Spotlight
The “Earth As Art” exhibit debuted in 2001 at the Washington Pavilion of Arts and Science in Sioux Falls with enthusiasm from the public and also visitors from USGS Headquarters. From there, its fame spread.
The USGS Headquarters decided Earth As Art should grace its halls in Reston, Virginia. Then people from Congress wanted to hang Earth As Art, Christopherson recalled. The Library of Congress followed—and then the media became aware.
“All sorts of other people wanted it for other things,” Christopherson said. “It just grew. Pat, Ron and I were on South Dakota Public Radio. I got interviewed by CNN, AP … and then it hits the wires, and I’m getting emails from people in Munich. From Brazil.”
And then, Christopherson’s dream of a coffee table book came true. Someone from the German Space Agency had come to United States with the vague intention of making a coffee table book, and after a couple stops at NASA locations, he had been directed to USGS EROS. He came away knowing he wanted to include Landsat 7 imagery in the book. A related display containing Landsat 7 imagery also traveled around to German cities.
Scaramuzza discovered, during a recent trip to the Science Museum of Minnesota, that Earth As Art images he had worked on were hanging on a wall there, too. “It surprises me whenever I find it in the wild,” he said.
One company attracted to Landsat 7 imagery was Google. EROS had the capability to process a little more than 100 scenes a day at that point, but Google wanted far more: cloud-free scenes for the entire globe. “That would take years,” Kline said.
So, Google and the USGS made an agreement that enabled Google to bring a lot of equipment to EROS to help speed up processing. “And all of that data became the first version of Google Earth,” Kline said.
Harrowing Malfunction
Anyone familiar with Landsat 7 knows that, despite its successes, the satellite also suffered a major misfortune. All Landsat 7 imagery became marred from May 2003 forward because the Scan Line Corrector within the ETM+ instrument stopped working.
The Scan Line Corrector, which compensates for the forward motion of the satellite, could no longer remove the typical “zigzag” motion caused by the differing movements of the scan mirror in the ETM+ and the spacecraft itself that results in some duplicate data. Landsat 7 scenes, after the failure, had gaps where duplicate data was removed that represent the loss of 22% of the data in each scene.
This affected EROS immediately, as some people tried to help figure out what went wrong and others tried to devise ways to fill the gaps of missing data.
Christopherson had left the Image Assessment System to take a different role at EROS. But he was called in to serve on a quickly assembled troubleshooting team because Hayes, the new Image Assessment System leader, was away with the National Guard.
Christopherson made himself useful. He had brought ETM+ schematics with him from Santa Barbara, and when other copies couldn’t be found elsewhere, he ended up photocopying all the prints to send to NASA, also on the troubleshooting team along with Hughes. The schematics helped Christopherson and his EROS colleague Jim Storey conclude that the Scan Line Corrector motor still had voltage, so lack of power hadn’t caused its demise. NASA came to the same conclusion after seeing the schematics, Christopherson said.
Coincidentally, EROS, which offers tours to the public, had been displaying an engineering model of the ETM+ instrument in its atrium since soon after the launch of Landsat 7. In fact, Scaramuzza admitted he and his team climbed over the barrier surrounding the model to “crawl all over that thing” and figure out how the different parts worked to acquire the data that they were looking at.
When the Scan Line Corrector failed, people remembered that a replica of it existed—somewhere at Hughes Santa Barbara, they thought, where it had been assembled with parts dating to the development of the earlier Landsat 4 and Landsat 5 satellites.
Christopherson wondered whether the replica might, in fact, be embedded in the ETM+ at EROS. So, he climbed over the barrier, reached a digital camera into the telescope and took a flash photo. Sure enough, he had found it.
The Scan Line Corrector was removed and sent to Santa Barbara for testing to see if the problem could be replicated to help determine its cause. Testing was inconclusive, and the cause of the failure remains a mystery circling hundreds of miles above Earth.
“The leading theory was that there’s an epoxy that was used as part of the turning mechanism in the Scan Line Corrector that might have come unglued because of age,” Kline said.
‘Stressful Time’ at EROS
As Landsat 7 Mission Manager at the time, Kline had received plenty of calls in the middle of the night about various problems with flight operations or data processing. But the Scan Line Corrector failure was devastating in its permanent defect.
“That was an extremely stressful time for the project,” Kline said.
“At the time, we sold the data, so it was going to affect our sales,” Sauer elaborated. His efforts revolved around trying to make the data as usable as possible, despite the gaps. “We were all kind of biting our fingernails. Are we going to be able to afford all the people we have? Are we going to be able to afford our systems? How is our budget affected? It worked out, but it was pretty tense. At the time, you didn't know what was going to happen.”
As it turned out, Landsat 7 had plenty of life left. The USGS decision in 2008 to open the Landsat archive up and cease charging for data sent downloads from the EROS archive soaring. Scientists around the world found a wide variety of ways to make use of the plethora of data from Landsat 7 and previous missions.
Devoted Flight Operations Team Members
Five people on the 13-member Landsat 7 Flight Operations Team (FOT), based at NASA Goddard, worked to operate and maintain the health of the satellite and the ETM+ for the full quarter-century. Even longer, actually—the team also worked with the satellite builder before launch on design and operations aspects.
The current members have spent an average of 18 years working with Landsat 7.
“In the early days, we celebrated spacecraft milestones, birthdays, weddings and the birth of children. Now those celebrations include retirements,” members of the Flight Operations Team wrote in a collection of Landsat 7 memories.
The team, led by Tom Cooke, worked closely with people based at EROS. “I walk in there, and I've known these people for 25 years,” Kline said. “They absolutely are going to stay with the mission until the mission is done. The dedication to that mission is phenomenal.”
Despite challenges, which included 9-11, snowstorms and the COVID-19 pandemic, the Flight Operations Team recalled that “there has not been a day in 25 years that the team has not come to the control center to command Landsat 7.”
Two people on the team, Tim Wilcox and Sang Lee, even spent a decade on double duty. They worked on the Landsat 7 team in Greenbelt, Maryland, and also worked on Landsat 5’s team in Columbia, Maryland, until that satellite’s 2013 decommissioning.
‘It’s Been Quite a Ride’
Daniels stepped away from Landsat 7 for a decade or so. But then he was drawn back into the satellite’s realm to help with its late-in-life extended science mission. The satellite was lowered in 2022 out of the orbit currently occupied by Landsat 8 and Landsat 9 but continued to collect data until January 2024.
During discussions about the end of Landsat 7 science, Daniels said, “it was very interesting for me to think back to starting at EROS because of Landsat 7. That’s what brought me home—I’m originally from Sioux Falls. It’s been quite a ride. This is the first mission that I’ve worked where I’ve actually been part of the beginning and the end.”
Landsat 7 certainly benefited EROS, Daniels reflected. “Landsat 7 was the proving ground for us. And you know that the best way to get future work is to do really well at the work you have today. The team really did a nice job. And because Landsat 7 was done well by USGS, we were able to take on a larger role with Landsat 8 when that came around.”
Kline, who herself retired from EROS this year, marveled that Landsat 7 and its technology were able to keep functioning for 25 years—especially considering its design life was 5 years. “Think back to what your computer was like 25 years ago,” she posed, “and imagine that still being on your desk and you still trying to use it.”
Even though the spacecraft no longer transmits imagery, its decades of data will continue to be used indefinitely along with other Landsat data in the quest for scientific answers.
And a new mission will come along to add even more data. Landsat Next, with its three-satellite configuration, is slated to launch in late 2030/early 2031.
“You look back in your career, and you're like, well, Landsat 7 came—that’s kind of what brought us here. But it was the beginning,” said Sauer, who currently serves as Acting Branch Chief for New Missions at EROS, which includes helping oversee preparations for Landsat Next.
“So, of those that come now for Landsat Next, it's the new beginning for them. Hopefully they come experience another 27 years, 30 years or more.”
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