Detection of red edge position and chlorophyll content by reflectance measurements near 700 nm

Pigment contents as determined in a high spectral resolution reflectance measurements were acquired for spring, summer and autumn maple and horse chestnut leaves covering a wide range of chlorophyll content. Consistent and diagnostic differences in the red edge (680-750 nm) of the reflectance spectrum were obtained for the various leaf samples of both species studied. This included the differences in the wavelength position of the red edge and in the reflectance values in the range of 690 to 710 nm. Both characteristics were found to be dependent on leaf chlorophyll concentration. The first derivative of reflectance spectra showed four peaks at 685-706, 710, 725 and 740 nm that were dependent in different degrees on leaf age and pigment concentration in the leaves. The position and the magnitude of the first peak showed a high correlation with the leaf chlorophyll concentration. Reflectance at 700 nm was linearly dependent on the wavelength of the first peak. Variation of inflection point position with change in chlorophyll content was found small for yellow-green to dark green leaves (total chlorophyll in the range above 10 nmol/cm²), reflectance near 700 nm was found to be a very sensitive indicator of the red edge position as well as of chlorophyll concentration. The ratio of reflectances at 750 nm to that near 700 nm (R₇₅₀/R₇₀₀) was directly proportional (correlation r²>0.95 to chlorophyll concentration. The ratio R₇₅₀/R₇₀₀ as a newly established index for non-invasive in-vivo chlorophyll determination was rested by independent data sets in the range of Chl contents from 0.6 to more than 60 nmol/cm² maple and chestnut leaves with an estimation error of Chl of less than 3.7 nmol/cm².