Abstract

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 = ∑aiλi, (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.

© 1970 Optical Society of America

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