Areal determination of the influence of a forest canopy on the surface radiant energy exchange

To accurately model the energy balance of an alpine snowpack, the influence of a vegetation canopy on the surface radiant energy exchange must be known. A number of studies have been conducted to determine the shading effects of a canopy at a point. This paper presents a new method of estimating canopy cover density which can be extended over a large area. Canopy shading functions, developed from photographic techniques, describe the proportion of the hemisphere surrounding a point which is partially obscured by vegetation. A general diffuse shading function and a beam shading function which account for changes in solar zenith are presented. Both functions account for changes in canopy cover density with variations in snow depth. The technique presented is to be modified and tested during summer, 1980, so that it can utilize Landsat satellite data to determine canopy densities over a large area. The shading functions can then be used in areal models of solar and terrestrial radiation.