Variations of albedo and spectral reflectance on Qiyi Glacier in Qilian Mountains during the ablation season
Updatetime：2011-07-07From：
【Enlarge】【Reduce】
Based on the data observed at two sites (site H1, 4,473 m a.s.l., and site H2, 4,696 m a.s.l.) on Qiyi Glacier in Qilian Mountains, China, by automatic weather station and spectral pyranometer during the period of June 9 through September 27, 2006, we investigated the temporal and spatial variations in surface albedo and spectral reflectance on the glacier. At site H1, the daily mean surface albedos fluctuated between 0.233 and 0.866, which were significantly affected by the air temperature on the glacier. It was found that the albedos clearly showed a diurnal cycle with the lowest value at noon at the two observation sites over the study period, and the difference of albedos between the upper site H2 and the lower site H1 also showed diurnal cycle but with the highest value at noon. The reflectance on the glacier was higher in the ultravio-let (0.28–0.4 μm) and visible (0.4–0.76 μm) wavelengths, lower in the near infrared wavelength (0.76–3 μm), which is quite contrary to the spectral reflectance on other ground surfaces. At the two observation sites, the spectral reflectance declined in all wavelengths with the ablation of snow generally. However, it declined drastically in ultraviolet (0.28–0.4 μm) and 0.6–0.7 μm wavelength, and declined less in 0.4–0.5 μm wavelength. On fresh snow surface, the spectral reflec-tance had the high values of 0.983 and 0.815 in the ultraviolet and visible (0.4–0.76 μm) wavelengths, respectively; but it had a relatively lower value of 0.671 in near infrared (0.76–3 μm) wavelengths. However, on dirty and melting ice sur-faces, the reflectance had the very low values of 0.305 and 0.256 in the ultraviolet and visible wavelengths, with the low-est value of 0.082 in near infrared wavelengths. The spectral reflectance also showed a diurnal cycle like that of albedo. The diurnal variations of spectral reflectance on snow surface in ultraviolet and visible wavelength changed to a greater degree than that on ice surface. The diurnal variation curves were asymmetrical before and after the local noontime, but the curves on ice surfaces in every wavelength were relatively flat and symmetrical. Especially, the surface reflectance in near infrared wavelength was flat and symmetry on both snow and ice surfaces. The studies of relations between the snow albedo and snow density and impurity, and the impact of glacier albedo on the glacier runoff are also described in this research.
Appendix
