ABSTRACT

Numerous satellite optical sensors have been launched and planned for launch for monitoring and characterization of the Earth system and its behaviors. These sensors have been providing and will continue to provide systematic observations of terrestrial vegetation at various spatial, spectral, and temporal resolutions. Spectral vegetation indices (VIs) are among the most widely used satellite data products in monitoring temporal and spatial variations of vegetation photosynthetic activities and biophysical properties. VIs are optical measures of vegetation canopy “greenness,” a direct measure of photosynthetic potential resulting from the composite property of total leaf chlorophyll, leaf area, canopy cover, and structure [1]. Although they are not intrinsic physical quantities, VIs are widely used as proxies in the assessments of many canopy state and biophysical process variables, including leaf area index, fraction of absorbed photosynthetically active radiation, vegetation fraction, and gross primary production (e.g., Refs. [2,3]).