The variations of spectral hemispherical reflectance (albedo) in vegetation canopies were studied as a function of solar zenith angle, leaf area index, led orientation distribution, and leaf and soil optical, properties. A three dimensional radiative transfer model was used to investigate the radiative transfers that give rise to variations in hemispherical relfectance (ρ). The results of this model were compared to those derived using an analytical two-stream approximation model which has the advantages of being simple and robust enough to use in real time applications. The hemispherical reflectance in the visible and near-infrared regions can vary as much as 60% with changes in solar zenith angles from 0° to 77°. This variation generally decreases as the leaf orientation distribution approaches a planophile distribution. The probability of gap function through the canopy and the spectral characteristics of the soil and vegetation are key factors in determining the hemispherical reflectance dyna... Abstract The variations of spectral hemispherical reflectance (albedo) in vegetation canopies were studied as a function of solar zenith angle, leaf area index, led orientation distribution, and leaf and soil optical, properties. A three dimensional radiative transfer model was used to investigate the radiative transfers that give rise to variations in hemispherical relfectance (ρ). The results of this model were compared to those derived using an analytical two-stream approximation model which has the advantages of being simple and robust enough to use in real time applications. The hemispherical reflectance in the visible and near-infrared regions can vary as much as 60% with changes in solar zenith angles from 0° to 77°. This variation generally decreases as the leaf orientation distribution approaches a planophile distribution. The probability of gap function through the canopy and the spectral characteristics of the soil and vegetation are key factors in determining the hemispherical reflectance dyna...