‘Just madness’: Concerned scientists lobby to save space station’s forest-mapping laser

Since April 2019, a fridge-size instrument attached to the International Space Station (ISS) has tickled the treetops of much of the planet with laser light, mapping forests’ carbon stores and the wildlife habitat they provide. Yet in early 2023, the laser is set to be jettisoned into Earth’s atmosphere, where it will burn up unless NASA approves a plan to extend its tenure. Researchers and some U.S. Congress members are now lobbying NASA to give the Global Ecosystem Dynamics Investigation (GEDI) instrument a second life so it can finish measuring the world’s tropical and temperate forests.

“To take that data source off is just madness, given that we haven’t even achieved global coverage,” says Matt Finer, a researcher for the Amazon Conservation Association. GEDI is “one of a kind,” adds Sarah Carter, a researcher at the World Resources Institute. Compared with previous instruments, it has given forest measurers “much more nuanced data.”

Imaging satellites such as Landsat can map forests, but have limitations: They can only tell whether trees are there, not how tall they are, what quality habitat they provide, or how much carbon they hold. Planes equipped with radarlike laser instruments called lidars can gather more informative forest measurements, but such flights are costly.

GEDI has used its perch on the ISS to deploy lidar over much of the globe. As the station hurtles around the planet, GEDI pings the surface with 242 pulses per second of near-infrared light and measures the reflections. The focused radiation penetrates dense canopies but bounces back from treetops, midstory branches, and the ground, enabling researchers to produce 3D forest images and estimate the wood and carbon they store. GEDI has enabled “unquestionably the best map of canopy height that’s ever been produced,” says Ralph Dubayah, an ecologist at the University of Maryland, College Park, and leader of the GEDI team.

Already, the instrument has identified the parts of the Amazon rainforest that hold the most carbon, Finer says—a finding he says “could drive a whole new line of carbon-based conservation.”

GEDI is also helping some countries, such as Paraguay, improve forest carbon estimates, which are required in climate reports. In the United States, GEDI has revealed that trees in areas unmonitored by the U.S. Forest Service hold a surprisingly large amount of carbon that isn’t included in the country’s greenhouse gas reporting, says USFS researcher Sean Healey. The instrument’s data could also boost emerging carbon markets that pay forest owners for carbon sequestered in their trees, he adds.

Field measurements help calibrate GEDI’s carbon estimates. The team has no ground data from China and very little from Indonesia, making estimates in those countries less accurate, Dubayah says. Others say the problem is broader and might limit GEDI’s role in verifying compliance for carbon markets and climate treaties. “We need a methodology to validate these maps that is based on high-quality ground data,” says Jérôme Chave, a tropical forest researcher at the French national research agency, CNRS, in Toulouse.

Scientists have also used GEDI for biodiversity research. In a study published in September, wildlife researchers studying ecosystems around Wyoming’s Yellowstone National Park found that GEDI data improved their modeling of coyote, red squirrel, and snowshoe hare habitat. At the global scale, GEDI-based maps are now being used to target conservation efforts to forests with complex structures known to harbor more species, says Scott Goetz, a geographer at Northern Arizona University and GEDI co-lead.

From early 2020 to late 2021, an unexpected change to the ISS orbit caused GEDI to repeatedly map the same forests while missing others; the resulting data gap is a big reason why team leaders want an extension. Nevertheless, GEDI is scheduled to get the boot in early February 2023 to make way for a long-planned Department of Defense sensor that will collect hyperspectral images to train artificial intelligence systems. After U.S. Senator Chris Van Hollen (D–MD) heard about the planned eviction, he rounded up congressional colleagues and, in August, wrote to NASA Administrator Bill Nelson to ask him to extend GEDI. They developed a proposal to shelve the instrument for 18 months on the ISS and then reinstall it for another round of data collection. The plan must still pass a NASA review, but Van Hollen “feels confident it will result in a positive outcome.”

A NASA spokesperson noted that GEDI is one of seven Earth-observing instruments on the ISS, three of which are being considered for extensions. She said the NASA review of GEDI, set for next month, will consider the costs and benefits of extending the mission, which would involve “multiple complex operations.”

If NASA sends GEDI to the satellite graveyard, ICESat-2, a lidar satellite designed to measure ice thickness, will continue to gather forest measurements, including in the boreal regions of Canada and Russia that GEDI misses because of the low-latitude ISS orbit. Two upcoming radar satellites could also help fill the gap. And researchers have used machine learning to find correlations between GEDI and Landsat data, raising hopes that the latter alone could continue tracking carbon loss from deforestation in some areas.

But nothing would beat having the real thing around in 2025 and beyond to capture how forests are changing with time, says Laura Duncanson, a University of Maryland, College Park, geographer also on the GEDI team. “If GEDI gets extended, it’s going to open this massive door into change mapping,” she says. “It will be scientifically explosive.”