Phenological influences on the albedo of prairie grassland and crop fields.

摘要

The relationships between albedo and plant phenology in prairie grassland and agricultural crops were examined by removing the effect of variations in solar zenith angle (thetas). Albedos were evaluated at a constant thetas, which was assigned to be20degree C in this study. For days with a minimum thetas larger than 20degree C, a polynomial function that relates albedos to thetas was derived and applied to estimate the albedos at 20degree C. After the removal of thetas variations, the observed albedos of grassland atthe Konza Prairie showed a linearly decreasing trend from spring to winter due to prairie phenology. The observed albedo of a maize field showed a clear increase from seedling to peak green stage, except when drought caused a decrease in near-infrared reflectance. The observed albedos of a winter wheat field showed an uninterrupted decrease from peak green to harvesting stage.