Researchers have developed a new approach using data from NASA's Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) satellite to observe the timing and progression of fall colors across landscapes.
The study, published in Remote Sensing Letters and led by Karl F. Huemmrich , a research professor at UMBC's Goddard Earth Sciences Technology and Research (GESTAR) II center, focuses on detecting changes in leaf pigments including chlorophylls (greens), anthocyanins (reds), and carotenoids (yellows and oranges).
PACE's advanced sensors capture fine details of light reflected from leaves, with near-daily global coverage. The research team used indices that associate the reflectance data with the presence of various pigments, allowing them to produce detailed leaf color maps and track color changes throughout the fall. These maps could help support the multi-billion-dollar leaf-peeping tourism economy by directing visitors to peak viewing areas in real time and helping communities manage visitor flows.
Traditional greenness indices, such as the Normalized Difference Vegetation Index (NDVI) , primarily show a gradual decline in green leaves. The PACE-based indices improve on those methods by allowing scientists to identify more precise markers of the end of the growing season, including dates of peak fall color. Over time, the data could also yield insights into plant stress from drought or insect damage—with potential benefits for agriculture—and help improve models that predict fall color timing based on environmental conditions.
"PACE is the first mission that can measure these pigment indices over large areas, and repeatedly, so we can look at change through the fall," Huemmrich says. The indices he and Caplan used were developed in the early 2000s, but the new paper applied them at a global scale for the first time. Huemmrich adds, "I anticipate that as we accumulate more years of PACE data, we will be able to observe changes in the timing of peak color, which may be related to climate change."
Opening frontiers in ecosystem science
Study co-author Skye Caplan, a NASA data scientist, expressed enthusiasm about the broader research potential unlocked by PACE. "I'm excited about observing fall colors with PACE, because I think it's the beginning of a real exploratory period for global hyperspectral leaf pigment measurements," she says. "I'm hoping we get to see folks read the paper, see how PACE observes these metrics like relative chlorophyll, anthocyanin, and carotenoid content, and apply those observations to their own work."
"Working with PACE data is really fun, because you get to see the world in so many different ways," Caplan adds. "It doesn't just offer observations of the oceans, but also characterizations of the atmosphere and land—and all of these domains as a system, rather than as separate entities. I think that is critical and a real advantage of PACE."
For example, Huemmrich previously published research that used PACE data to assess ecosystem productivity , and the UMBC-designed and -built HARP2 instrument flying on PACE is contributing to atmospheric chemistry studies.
Plus, PACE observations aren't only for scientists: Caplan notes that the public can access NASA Worldview , an interactive site for browsing satellite images from many different NASA missions. "Sometimes I like to pull up PACE data on NASA Worldview and just scroll around to see what the world looked like on any given day," she says. "I often find something interesting and worth exploring."
