Remote sensing of forest canopy and leaf biochemical contents

Abstract

Remote detection and measurement of the nitrogen and lignin contents of forest canopies could allow predictions of biogeochemical processes such as productivity, decomposition, and nutrient turnover rates. Spectral absorption features characteristic of proteins (containing nitrogen), lignin and other leaf constituents occur throughout the shortwave infrared region (1200–2400 nm). The lignin and nitrogen concentration of dried and ground deciduous leaves have been predicted from reflectance spectra obtained in the laboratory. The optimum wavelengths for prediction were selected using stepwise multiple linear regression. The prediction errors were comparable to chemical techniques. Analysis of the reflectance spectra of fresh, whole leaves has been limited thus far to conifer leaves but indicate spectral features predictive of nitrogen and lignin also found in airborne spectra. Airborne Imaging Spectrometer (AIS) were evaluated for whole forest canopy physical and chemical properties. Variations in spectral brightness were associated with variations in total water content of the foliar biomass. Comparison of forest spectra with spectrally flat targets revealed absorption features common to the canopy spectra between 1500 and 1700 nm which were tentatively attributed to absorption by lignin and starch. The AIS and laboratory data indicate strongly that absorption in the infrared region is influenced by biochemical characteristics.