RED EDGE SPECTRAL MEASUREMENTS FROM SUGAR MAPLE LEAVES

Many sugar maple stands in the northeastern United States experienced extensive insect damage during the 1988 growing season. Chlorophyll da ta and high spectral resolution spectrometer laboratory reflectance da ta were acquired for multiple collections of single detached sugar map le leaves variously affected by the insect over the 1988 growing seaso n. Reflectance data indicated consistent and diagnostic differences in the red edge portion (680-750 nm) of the spectrum among the various s amples and populations of leaves. These included differences in the re d edge inflection point (REIP), a ratio of reflectance at 740-720 nm ( RE3/RE2), and a ratio of first derivative values at 715-705 nm (D715/D 705). All three red edge parameters were highly correlated with variat ion in total chlorophyll content. Other spectral measures, including t he Normalized Difference Vegetation Index (NDVI) and the Simple Vegeta tion Index Ratio (VI), also varied among populations and over the grow ing season, but did not correlate well with total chlorophyll content. Leaf stacking studies on light and dark backgrounds indicated REIP, R E3/RE2 and D715/D705 to be much less influenced by differences in gree n leaf biomass and background condition than either NDVI or VI.