Plant leaves grown in a greenhouse and leaves collected from the field have been analyzed to obtain mean effective optical constants based upon diffuse reflectance and transmittance measurements taken over the 0.5–2.5-µ spectral range. These optical constants are used in a generalized flat-plate model to describe the phenomena of leaf reflectance. Analysis procedures developed led to measures of the amount of water and intercellular air spaces in the leaves. Over the 1.4–2.5-µ spectral range, the absorption spectra of leaves are not statistically different from that of pure liquid water. Leaf reflectance differences among the plant leaves over the 0.5–1.4 µ range are caused principally by Fresnel reflections at external and internal leaf surfaces and by plant pigment absorption. Reflectance over the 1.4–2.5-µ range results largely from Fresnel reflections and absorption by water. Data are presented in the form of dispersion curves with 95% confidence bands and tabulated plant leaf absorption spectra. The dispersion curves were assumed to be cubic equations of the form n = Σaiλi (i = 0, 1, 2, 3), where λ is wavelength. Reflectance measurements at 1.65 µ have been associated with the equivalent water thickness and the intercellular air spaces in the leaf. Accuracy of the plate theory based upon a cubic dispersion curve is shown to be within experimental error.
W. A. Allen, H. W. Gausman, A. J. Richardson, and C. L Wiegand, "Mean Effective Optical Constants of Thirteen Kinds of Plant Leaves," Appl. Opt. 9, 2573-2577 (1970)