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.