LIBERTY—Modeling the Effects of Leaf Biochemical Concentration on Reflectance Spectra

The conifer leaf model LIBERTY (Leaf Incorporating erties of individual leaves (Aber, 1994). Leaves are an Biochemistry Exhibiting Ref lectance and Transmittance important component of forest canopies, and it is the Yields) is an adaptation of radiative transfer theory for deconcentration of their biochemical constituents, namely, termining the optical properties of powders. LIBERTY pigments, water, nitrogen, cellulose, and lignin, together provides a simulation, at a fine spectral resolution, of with canopy structure that shapes the absorption features quasiinfinite leaf ref lectance (as represented by stacked of remotely sensed ref lectance spectra. Absorption fealeaves) and single leaf reflectance. Single leaf ref lectance tures in the near infrared region of the spectrum (1000– and transmittance are important input variables to vegeta2500 nm) are a function of the bending and stretching tion canopy reflectance models. A prototype parameterizavibrations of biochemical bonds (between, for example, tion of LIBERTY was based upon measurements of pine hydrogen–carbon and nitrogen–oxygen atoms) together needles and known absorption coefficients of pure compowith their harmonics and overtones (Kemp, 1987). In the nent leaf biochemicals. The estimated infinite-reflectance visible region, chlorophyll and carotenoid pigments have output was compared with the spectra of both dried and strong absorption due to electron energy transitions fresh pine needles with root mean square errors (RMSE) (Lichtenhaler, 1987; Mackinney, 1941). Fine spectral of 2.87% and 1.73%, respectively. The comparisons beresolution remotely sensed data can be statistically anatween measured and estimated ref lectance and transmitlyzed to estimate the concentration of biochemicals in tance values for single needles were also very accurate forest canopies. Such information has been used to drive with RSME of 1.84% and 1.12%, respectively. Initial inecosystem simulation models and estimate photosynversion studies have demonstrated that significant imthetic efficiency, the rate of nutrient cycling, and the deprovements can be made to LIBERTY by utilizing in vivo gree of vegetation stress (Curran, 1994). Strong correlaabsorption coefficients which have been determined by tions between leaf biochemical concentrations and the inversion process. These results demonstrate the caspecific wavebands of measured spectra have now been pability of LIBERTY to model accurately the spectral rereported by Wessman et al. (1988), Martin and Aber sponse of pine needles. Elsevier Science Inc., 1998 (1990), Curran and Kupiec (1995), and Zagolski et al.