Phenology is the study of the timing of biological events, particularly in response to climatic changes to the environment. Certain biological events, such as the time of the start of the growing season, have a key role in changing land surface/atmosphere boundary conditions such as surface roughness, albedo, humidity, etc. The phenology of ecosystems and its connection to climate is a key to understanding ongoing global change.

Phenology has historically been studied as direct observations of the timing of leaf opening, flowering, leaf fall and such events. But to study large areas, remote sensing from satellites has emerged as an essential tool. In the Phenological Characterization project, we have developed methods of analyzing time-series vegetation index data to derive a set of phenological metrics.