Variations of surface albedo and its diurnal asymmetry at different growing stages of spring wheat in arid areas

Surface albedo greatly affects the radiation energy balance of the cropland and is a significant factor in crop growth monitoring and yields estimation. The research aimed to explore the variations of surface albedo with the transitions of different growing stages of spring wheat and analyze the diurnal asymmetry of surface albedo and its causing factor. Diurnal albedo variations were measured at different growing stages (tillering, jointing, heading, filling and maturity) of spring wheat by using a pyranometer. Results indicated that the daily mean surface albedo showed an increasing tendency during tillering to heading but decreased after heading. Surface albedos were much higher in the morning than its corresponding values of the same solar elevation angles in the afternoon when solar elevation angle was less than 40°, indicating a diurnal asymmetry of surface albedo. However, surface albedos showed less difference between forenoon and afternoon when solar elevation angle was greater than 40°. Dew droplets on the leaf surface in the morning were assumed to be the main causing factor for the diurnal albedo asymmetry of spring wheat. The study is expected to provide a reference for precisely specifying surface albedo and further monitoring crop growth using surface albedo in arid areas.