Radiative Transfer in an Array of Canopies1

Abstract Theories describing radiative transfer in plant canopies are very well developed for canopies approximating full cover. However, for canopies of partial cover such as orchards, wide‐row crops or widely spaced individual plants, no general theory exists. This paper contains a description of a general radiative transfer model that is capable of accommodating nearly any canopy structure. The plant canopy is approximated by an array of ellipsoidal subcanopies that may be equally spaced, randomly spaced, or spaced in any manner desired. Ellipsoids were chosen because of the infinite variety of shapes that they can approximate. All of the foliage of any individual subcanopy is contained within the confines of its ellipsoidal subcanopy, and assumed to be statistically distributed within the subcanopy volume with respect to location, foliage angle, and foliage area per unit of subcanopy volume. The radiative transfer model includes attenuation of direct beam and sky diffuse radiation, multiple scattering for visible and near‐infrared wavelength, and emission for thermal wavelengths. When the subcanopies overlap extensively, the predictions from the general ellipsoidal model approach the predictions from one‐dimensional models applicable to canopies of full cover. Predictions from this three‐dimensional model are compared with cross‐row measurements in a corn canopy. In addition, sunfleck area and sunlit‐leaf area comparisons are made between this three dimensional model and a one dimensional model for a developing corn canopy.