Adapted Analysis Technique Boosts Capabilities for Monitoring Forest Change

NDVI on linear graph and polar plotSatellite-derived NDVI values capture the “greenness” of vegetation and offer a state-of-the-art way to monitor changes in the nation’s forests and grasslands. Using NDVI data from the Eastern Threat Center's ForWarn monitoring system, researchers are conducting in-depth studies to develop monitoring tools that can complement direct surveys of forest plots. In particular, recent investigations have revealed that vegetation greenness can actually be analyzed through techniques borrowed from meteorology. Using a polar coordinates technique, researchers can re-project vegetation greenness in a polar plot—a graph that represents greenness measures through time in a radial, or circular, format—and extract a wide range of measures, including growing season length, greenness variability, and start-of-spring date, that directly indicate the state of a given parcel of land at fine (sub-hectare) resolution. Since researchers extract these measures from data in a polar context, they can compare them coast-to-coast and basin-to-range, and then analyze them for changes that are not biased by elevation, latitude, or location. This is a useful advance that makes further analysis of complex information about vegetation data faster, more intuitive, and standardized for each location’s local environment. Researchers can then map, data mine, or clip out specific seasons to search for anomalies in vegetation greenness such as defoliation by gypsy moth.

Pictured: Vegetation greenness (NDVI) data over 12 years for a single pixel in western North Carolina is shown on (a) a conventional linear graph, and (b) a polar plot. In polar plot (c), the start of the year is adjusted to match the start of this location’s growing season. Click to enlarge.

External Partners/Collaborators: Oak Ridge National Laboratory

Contact: Bjorn Brooks

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