Mean Effective Optical Constants of Thirteen Kinds of Plant Leaves

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-micro 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-micro 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 micro 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-micro 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 = Sigmaa(i)lambda(i) (i = 0, 1, 2, 3), where lambda is wavelength. Reflectance measurements at 1.65 micro 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.