Albedo of a Forest Modeled as a Plane with Dense Protrusions

Abstract A model is developed that treats, in a simplified way, the reflection of the direct solar radiation by a surface consisting of a soil-plane and protruding vertical plant elements, such as needles of pine trees or stalks of a wheat field. Such a surface is treated as a Lambertian reflectivity soil-plane (reflectivity ri) and thin, vertical cylinders are also characterized as Lambertian reflectors (reflectivity rc). Each cylindrical section is randomly located with respect to the other sections. The first hemispheric reflection of the direct beam from this surface is computed exactly, expressed as diri + dcrc, where di and dc are the geometrical factors governing the reflection from the soil-plane and from the protrusions respectively. These geometrical factors are a function of the solar zenith angle θ0, and the area s of the projections on a vertical plane of the cylindrical plant elements per surface unit area. The light trapping in such a complex surface is assessed by analyzing di and dc. For ...