SPECULAR AND DIFFUSE COMPONENTS OF RADIATION SCATTERED BY LEAVES

Bidirectional reflectance and transmittance of oak and maple leaves were measured in the principal plane with a laboratory goniometer. Illumination was with linearly polarized visible and near-infrared radiation. The parallel and perpendicular polarization components of the scattered radiation were resolved with linear polarizers and used to determine the specular and diffuse components. The specular reflectance was similar in the visible and near-infrared regions. The diffuse reflectance was lower in the visible because of absorption by plant pigments. Scattering from the abaxial surface was less specular than that from the adaxial surface because of surface roughness. Diffuse reflectance of visible radiation from the abaxial surface was increased by scattering from the spongy mesophyll. The specular component of the reflectance was used to compute K, the surface roughness correction factor for estimates of the specular reflection as specified by Fresnel's equations. Values of K greater than one were found to be possible, with K dependent not upon wavelength, but upon the incident angle of the radiation, the index of refraction, and surface roughness.