In the foreground, the GEDI instrument appears as a large white box. In the background, an astronaut climbs along the space station’s external scaffolding.
GEDI (right foreground) is mounted on the space station’s Japanese Experiment Module – Exposed Facility. In the background, an astronaut performs a spacewalk. Credit: Astronaut David Saint-Jacques

A controversy is brewing between remote sensing scientists and administrators from NASA and the agency’s international partners. The debate centers around how long the Global Ecosystem Dynamics Investigation (GEDI) lidar system will continue to operate from the International Space Station before the system is decommissioned and left to burn up in the atmosphere.

“To just burn up a mission that’s actually helping solve this problem is bonkers to me.”

Since 2019, scientists have used GEDI to discern characteristics of the land below. Among all the instruments in space, GEDI’s lasers have the unique ability to penetrate forest canopies and provide information about the height and structure of vegetation. Remote sensing scientists say the system gives them unparalleled opportunities to assess how much carbon forests store—a capability that could be critical for curbing climate change. But GEDI is slated to be decommissioned in March 2023, and these opportunities may go with it. The GEDI team is pushing for the project’s end date to be extended an additional year.

Laura Duncanson, a remote sensing scientist at the University of Maryland and a member of the GEDI team, points to dire climate projections in the most recent Intergovernmental Panel on Climate Change report as clear justification for GEDI to continue operating. “To just burn up a mission that’s actually helping solve this problem is bonkers to me,” she said.

GEDI deputy principal investigator Scott Goetz agrees. “It’s just the worst possible time to be removing this instrument,” he said.

A Decades-Long Battle

Ralph Dubayah, GEDI’s principal investigator, started trying to get a vegetation-penetrating lidar system into space in 1997. NASA canceled the first project he took part in—a mission to launch a satellite-based system—after the engineering team ran into technical problems. A subsequent project aimed to launch two satellites, one carrying lidar and the other carrying radar, which provide complementary information. Budget concerns became the second project’s downfall. Dubayah said that he and his colleagues thought, “Well, maybe we can put it on the space station.” It took two attempts to get NASA to fund the GEDI mission, but in late 2018, the instrument finally launched.

The problems weren’t over, however. The space station’s orbital altitude varies, for example, to avoid debris or to counter its slow fall toward Earth, and high altitudes cause the station to pass over the same parts of Earth repeatedly rather than crisscrossing regions. Dubayah says that after GEDI was installed, the space station cruised to an altitude that prevented the instrument from collecting more than a fraction of the data the team had hoped to get and also affected several other instruments. Dubayah and his colleagues worked with NASA and the agency’s partners to adjust the altitude variations, but the process was completed only recently. NASA agreed to extend GEDI’s stay on the space station by an additional year (to 2023) to compensate.

With GEDI finally functioning properly, scientists are diving into the data to analyze forest ecosystems. Antonio Ferraz, a remote sensing scientist from the University of California, Los Angeles, and a member of the GEDI team, is looking for links between a forest’s structural diversity and its ability to store carbon and support diverse life-forms. “We need to know where to conserve both carbon and biodiversity,” Ferraz said. He hopes to find hot spots that are the best candidates for both.

Sharing Space

“I understand from a NASA perspective that they have to be a good neighbor and try to preserve goodwill for other instruments and give other instruments chances to get up there,” Dubayah said. But with GEDI finally running smoothly, he doesn’t think it makes sense to decommission the system next year. Lidar systems are “very hard to get into space and hard to keep working,” he explained. “Here you have one that’s working—that’s giving you the data you’ve been waiting for for 25 years. And yet you’re going to pull it out.” Because of the disruptions, he’s not sure GEDI’s currently scheduled run will allow researchers to obtain widespread coverage of Earth’s forests.

Maintaining GEDI will let scientists collect baseline information for countries that committed to halting deforestation during the 2021 United Nations Climate Change Conference (COP26), Duncanson said. Goetz pointed out that without additional time, scientists will miss the opportunity to combine in-depth, localized information from GEDI with broad-spanning data from two radar-carrying satellites that are set to launch next year. “That’d be a travesty,” he wrote in an email.

The Broader Community

“In the last 10 years—and GEDI has been a huge part of this—we’ve had a golden age of new modalities of remote sensing.”

Ryan Pavlick, a researcher from NASA’s Jet Propulsion Laboratory, says GEDI’s data have become valuable for scientists throughout the remote sensing community. “In the last 10 years—and GEDI has been a huge part of this—we’ve had a golden age of new modalities of remote sensing,” he said. He added that tools and tutorials created by the GEDI team have contributed to widespread use of their data.

“It was a game changer for us,” said João Pereira-Pires, a Ph.D. student at NOVA University of Lisbon who’s focusing on remote sensing. Part of Pereira-Pires’s research involves using GEDI’s data to monitor fuel breaks—cleared strips of forest intended to limit the spread of wildfires.

Keeping GEDI in the sky will require buy-in from NASA’s Earth Science Division and, ultimately, its partners in the International Space Station consortium. NASA spokesperson Tylar Greene wrote in an email that “GEDI is currently manifested on station through early 2023, and it is scheduled to be replaced by a new experiment (STP-H9).” According to a technical report (scientists involved in the project weren’t available for comment), STP-H9 will include a project on using artificial intelligence to analyze images obtained with a hyperspectral sensor for scientific and defense-related purposes.

—Saima Sidik (@saimamaysidik), Science Writer

Citation: Sidik, S. (2022), Scientists fight to keep lidar on the space station, Eos, 103, Published on 06 April 2022.
Text © 2022. The authors. CC BY-NC-ND 3.0
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