The Reflectivity of Deciduous Trees and Herbaceous Plants in the Infrared to 25 Microns

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Abstract
The present investigations were undertaken to determine the reflectivity of numerous deciduous trees and shrubs beyond the photographic infrared in the region of 1.0-25[mu]. The infra-red radiant source was the Globar, whose radiation was re-flected off the leaf surface at the desired angle by means of spherical mirrors and then focused upon the entrance slit of the infrared spectrometer. It was discovered that reflectivity of leaves in the infrared beyond 2[mu] is generally small, being less than 10% for an angle of incidence of 65[degree], and less than 5% for an angle of 20%. Reflection takes place principally at the outer epidermal surface, with about one fifth contributed by the epidermal-palisade cells boundary. The upper surface reflects more than the lower, old leaves more than young, and shade leaves more than sun leaves. For each of these the converse is true in visible light. The transmissivity of leaves is zero in the infrared beyond 1.0[mu], although transmissivity of the clear epidermis is 40% or more.