PREDICTING NITROGEN AND CHLOROPHYLL CONTENT AND CONCENTRATIONS FROM REFLECTANCE SPECTRA (400-2500 NM) AT LEAF AND CANOPY SCALES

An experiment was designed to determine whether chlorophyll and nitrogen concentrations could be predicted from reflectance (R) spectra of fresh bigleaf maple leaves in the laboratory, and, if so, whether the predictive spectral features could be correlated with chlorophyll and nitrogen concentration or content of simple canopies of maple seedlings. The best predictors for nitrogen and chlorophyll of fresh leaves appeared with first-difference transformations of log 1/R, and the bands selected were similar to those found in other studies. Shortwave infrared bands were best predictors for nitrogen, visible bands best for chlorophyll. In the shortwave infrared region, however the absolute differences in reflectance at critical bands was extremely small, and the bands of high correlation were narrow. High spectral and radiance resolution are required to resolve these differences accurately. The best shortwave infrared bands from the leaf scale were not good predictors of chemical content or concentration at the canopy scale; variability in canopy reflectance in the shortwave infrared region was at least an order of magnitude beyond that necessary to detect signals from chemicals. The variability in first-difference log 1/R on the canopy scale was related to the arrangement of trees with respect to direct solar radiation, instrument noise, leaf fluttering, and small changes in atmospheric moisture.