A new study using data collected by NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) satellite established a novel method to determine how productive plants are worldwide. The new remote sensing technique could help us better understand plants’ role in capturing carbon on a global scale and reveal how plants are responding to factors like changing water availability and temperature, with relevance for conservation, agriculture, and more.
The research, led by Karl F. Huemmrich, a UMBC research scientist with the Goddard Earth Sciences Technology and Research (GESTAR) Center II, shows that PACE’s advanced camera can track plant health by analyzing the light leaves reflect. By comparing these satellite observations with measurements taken on the ground, the study confirmed that the new method works across diverse landscapes, opening the door to improved global ecosystem monitoring.
Launched in February 2024, PACE’s Ocean Color Instrument (OCI) captures daily images of Earth that show how plants are responding to their environment in real time. While OCI’s primary mission is to study oceans (hence its name), it also collects data over land.
“Although they do not appear to be very active to us, plants are constantly making physiological adjustments to their environment, responding to factors such as changing light, temperature, humidity, water, and nutrient availability,” Huemmrich explains. A plant can change its leaf area, leaf orientation, and the prevalence of different leaf pigments, he says. All of those changes alter the intensity and wavelengths of light the plants reflect, which OCI detects.
“PACE provides almost daily repeat observations,” except for areas blocked by clouds, Huemmrich says. “This time series can be used to describe changes in vegetation productivity related to seasonal change, for example the timing of spring green-up and autumn senescence, or more transient effects, like droughts or cold snaps.”
This gif shows how PACE’s OCI “sees” plant productivity changing throughout the growing season across North America. (Skye Caplan)
One algorithm to track them all
Unlike older satellite methods, such as MODIS Gross Primary Productivity, which needed weather data like temperature and humidity to estimate plant growth, PACE relies solely on the light reflected by plants.
“By using the information from the spectral reflectance alone, we are letting the plants show us their responses to environmental conditions, rather than trying to predict their responses,” Huemmrich explains. This approach makes it easier to accurately capture short-term changes.
The study tested PACE’s data against ground measurements from National Ecological Observatory Network (NEON) sites across the U.S., covering everything from arctic tundra to tropical dry forests.
“The NEON sites were chosen to cover all of the major ecoclimate types within the U.S.,” Huemmrich notes, “and frankly, it was surprising that a single algorithm could do as well as it did across all of those very different vegetation types.” This success suggests the method can be used globally, and there are plans to include more sites worldwide in future studies to cover even more ecosystems.
Huemmrich stands 100 feet above the ground on a meteorology tower at the Smithsonian Environmental Research Center in Edgewater, Maryland. (Courtesy of Huemmrich)
“An entirely new view”
This research could transform how scientists track carbon sequestration—how plants absorb and store carbon dioxide, a key greenhouse gas—improving understanding of how different ecosystems influence climate change. The ability to spot stress events early could also help farmers and environmental managers act quickly to improve outcomes for crops and wildlife.
PACE’s global reach is a huge step forward. “I believe this new ability to describe global ecosystem dynamics opens up an entirely new view of the Earth’s ecological functioning that we really have not been able to see before,” Huemmrich says. Unlike earlier methods that relied on labor-intensive ground measurements or expensive airplane flights, PACE offers a cost-effective way to monitor ecosystems worldwide.
Moving into PACE’s second year, Huemmrich is excited to explore how plant responses change over time. “I’m interested in looking at year-to-year differences,” he says. “I want to see how best to use the spectral information for early detection of stress events. Can we learn to diagnose types of stress responses? Do these responses vary among different types of plants?”
These questions will drive future research, aiming to improve how we detect and understand plant stress across diverse ecosystems. PACE’s frequent, detailed satellite data will help scientists, policymakers, and conservationists protect ecosystems and understand how plants are responding to a changing world.
The findings were published in IEEE Transactions on Geoscience and Remote Sensing and co-authored by Petya Campbell, a UMBC research scientist with GESTAR II and senior author; Skye Caplan, Goddard Space Flight Center; and John Gamon, University of Nebraska–Lincoln.
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