Technical Note Grass chlorophyll and the reflectance red edge

The point of maximum slope in the reflectance spectra of leaves occurs around 690-740 nm and is termed the ‘red edge’. Strong correlations have been found between the red edge of leaves and the chlorophyll concentration of those leaves. Imaging spectrometers can record the red edge of canopies and strong correlations have been observed between canopy red edge and the chlorophyll concentration of leaves in those canopies; providing the canopies were optically thick and/or had spatially invariant biomass. This study investigated relations between (i) canopy red edge and the chlorophyll concentration of leaves, and (ii) canopy red edge and the chlorophyll content of the canopy for a grass canopy with a spatially variable biomass. The canopy red edge as recorded by an airborne imaging spectrometer was correlated more strongly with the chlorophyll content of the canopy (r = 0·93) than the chlorophyll concentration of the leaves (r = 0·86). These results suggested that in the absence of other information the most appropriate measure of chlorophyll to relate to the red edge of a grass canopy is content rather than concentration.