On October 7, 2024, a satellite 676 kilometers above Earth caught the first blush of red in the forests of Vermont—tiny pulses of anthocyanin pigment glowing in the data like embers in a cooling fire. By October 21, that red had swept south through the Appalachians, painting a vivid trail across the eastern United States, all captured in near-daily detail by NASA’s PACE satellite. For the first time in history, scientists can now track the seasonal surge of fall foliage pigments across continents with unprecedented clarity, thanks to a breakthrough method developed by UMBC’s Karl F. Huemmrich and NASA’s Skye Caplan. This isn’t just about beauty—it’s about understanding how ecosystems respond to a changing climate.
The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) satellite, launched to study ocean biology and atmospheric particles, has proven unexpectedly powerful on land. Its hyperspectral sensor detects subtle shifts in light reflected from leaves, allowing researchers to isolate not just green chlorophyll, but also red anthocyanins and yellow-orange carotenoids. Unlike traditional tools like NDVI, which only measure the decline of greenness, PACE’s pigment indices reveal the full color story of autumn, including the exact timing of peak color. This precision opens doors far beyond leaf-peeping.
In 2024, the team mapped the rise of anthocyanins across the eastern U.S. with near-daily coverage, showing how red pigments surged by over 40% in some regions within three weeks. These maps could soon guide tourists to peak foliage in real time, supporting a leaf-watching economy that generates over $8 billion annually in states like New Hampshire and Vermont. But the implications stretch further: early detection of pigment shifts can signal plant stress from drought or pests, offering farmers and forest managers a vital early-warning system. Over time, this data may refine predictive models for fall color, helping communities prepare for seasonal surges in tourism.
"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," says Huemmrich, whose team applied indices first developed in the early 2000s to global satellite data for the first time. Caplan, a NASA data scientist, sees PACE as a gateway to a new era of ecosystem science: "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."
And the data isn’t locked away in labs. Anyone can explore PACE’s view of the planet through NASA Worldview, an interactive platform that lets users scroll through daily snapshots of Earth’s surface. From tracking algal blooms to watching fall colors spread, PACE is revealing our planet as a dynamic, interconnected system. As the satellite continues its mission, scientists anticipate detecting long-term shifts in seasonal timing—potential fingerprints of climate change—written in the annual fade of green to red.