NASA’s PACE satellite tracks autumn colors from space

In the fall of 2026, NASA’s PACE satellite is detecting autumn color changes from orbit by measuring leaf pigments across the globe. The satellite’s Ocean Color Instrument (OCI) gathers reflected sunlight in 286 narrow spectral bands, allowing it to distinguish the subtle shifts in leaf chemistry that signal the arrival of fall. This capability marks the first time a satellite can track the three major vegetation pigment groups—chlorophyll, carotenoids, and anthocyanins—on a near-daily, global basis. NASA scientists say the repeated coverage enables them to build time-series maps of seasonal change that were previously impossible.

The changing colors of autumn stem from the breakdown of chlorophyll, the green molecule plants use to synthesize food. As cooler temperatures and shorter days reduce the sunlight-dependent production of chlorophyll, the green pigment fades, revealing other compounds that were always present in the leaves.

To monitor autumn color, NASA researchers compare the amount of red, orange, and yellow visible in forests against green, then follow that proportion across weeks to locate changing trees and pinpoint peak timing. The PACE-derived pigment indices do more than track visible color; they identify the end of the growing season and peak fall color dates more precisely than traditional greenness measures such as the Normalized Difference Vegetation Index (NDVI), which mainly registers a slow decline in green leaves. According to NASA’s PACE Mission, the satellite’s observations distinguish multiple pigment groups rather than only chlorophyll, yielding a richer vegetation picture than earlier global monitoring systems.

Karl Huemmrich, a vegetation scientist at the University of Maryland, Baltimore County, who is part of the PACE team, called the ability to repeatedly gather time-series data on carotenoids and anthocyanins globally a significant advancement. He noted that the satellite’s broad swath and frequent revisit times allow scientists to determine peak color changes anywhere on Earth.

During the 2026 fall season, PACE observed especially high vegetation redness across portions of northern and eastern Russia, northern Alaska, and northern Canada in the week of Sept. 29 to Oct. 4. In the following week, Oct. 5 to 11, redness in New England and upstate New York began to fade while expanding through large parts of the Midwest and Mid-Atlantic. The reddest zones in the East, including the Adirondacks in New York, the Green Mountains in Vermont, and the White Mountains in New Hampshire, contain many sugar maples and red maples that turn crimson in autumn. In marshy tundra across northern Alaska, Canada, and Russia, intense red readings likely come from grasses, mosses, sedges, bilberries, and blueberries rather than maples.

Earlier, in the fall of 2024, PACE mapped red and yellow pigments developing across the eastern United States, with the red signal rising week by week from early October into the third week.

Landsat 9, a separate NASA satellite, has also captured the seasonal transition in striking detail. Its Operational Land Imager (OLI), orbiting 438 miles (705 kilometers) above Earth, photographed vividly red leaves near Ripton, Vermont, on Oct. 3, 2026, as the area reached its highest redness. Earlier in the summer, the same instrument documented the Coppermine River past Kugluktuk, Nunavut, turning from green to orange between July 27 and Sept. 6, 2026. A seven-year study by NASA and South Dakota State University found that vegetation around Kugluktuk turns red, orange, and yellow in early September and peaks near mid-month, a period that can last a week or less in far northern regions.

Peak foliage color usually reaches Vermont, New York, and Maine in late September or early October, with higher elevations seeing the season arrive earlier. PACE observes daily or near-daily.

Leaf viewing supports a multibillion-dollar travel economy each fall. Real-time pigment maps could direct visitors to peak viewing areas and help communities manage crowds, according to reports in Earth.com and Phys.org.

To ensure the satellite data accurately reflects what people see on the ground, NASA’s PACE team participates in the GLOBE North American Phenology Campaign. Under this effort, NASA data scientist Skye Caplan publishes weekly vegetation redness maps, and the team requests public fall foliage photos to check the satellite observations against what is seen on the ground. The campaign’s maps show red appearing first at high latitudes in August and moving toward the equator through September and October.

Caplan also noted that pigment changes caused by drought or insect damage likely account for high redness that PACE sees in agricultural areas of Brazil, Australia, and Canada unconnected to wider seasonal patterns. These stress signals, she said, may help explain redness detected in farm regions that do not align closely with broad seasonal shifts.

Researchers hope that ground-checked PACE color data will support work on changing spring greening and fall timing, vegetation impacts on the carbon cycle, leaf color and wildfire risk, and early alerts for drought, pests, and disease. Karl Huemmrich expects that accumulating more years of PACE data will let scientists observe shifts in peak color timing that may relate to climate change, building a multi-year record of repeated pigment observations across seasons.

Skye Caplan, a NASA data scientist, emphasized that the ability to observe land, ocean, and atmosphere together allows for viewing the planet’s systems as a single, connected whole. The PACE satellite’s integrated design provides a distinct advantage in studying how different Earth domains interact, from the pigments in leaves to the properties of the oceans and the chemistry of the atmosphere.

Caplan expressed excitement about observing fall colors with PACE, calling it the beginning of a real exploratory period for global hyperspectral leaf pigment measurements — hyperspectral instruments capture light in many narrow bands.