天山乌鲁木齐河源1号冰川消融期反照率特征

消融期冰川反照率特征研究对于深入理解冰川消融过程及其对气候变化的响应机理具有重要意义。利用Landsat卫星影像反演反照率数据，MODIS逐日反照率产品数据以及野外观测反照率数据，分析了天山乌鲁木齐河源1号冰川2016年消融期（5—8月）反照率时空变化特征。研究表明：消融早期，冰川反照率空间变化不明显；消融中后期，总体上呈现随海拔的升高而增大的趋势，在平衡线附近增速最快。消融期冰川反照率整体呈下降趋势，而且在6—7月份变化最为剧烈。平衡线附近反照率时间变化尤其显著，积累区次之，消融区最弱。冰川反照率的时空变化主要由冰面特征决定。气温和固态降水是其驱动因素。冰川反照率随气温的升高而降低，但固态降水会打破其随气温的变化趋势，引起反照率的增加。污化物显著降低冰面反照率，尤其在可见光波段（380~760 nm）。此外，即使冰面特征相对均一，反照率还呈现随太阳入射角的增大而增大的趋势，主要由冰川局部地形（坡度与坡向）差异所致。

The characteristics of surface albedo on the Urumqi Glacier No.1 during the ablation season in eastern Tien Shan

Glacier albedo directly governs the net shortwave radiation flux at the glacier surface and largely determines the surface energy balance over entire glacier. Surface albedo is one of the important drivers of surface processes that promote glacier melting. Therefore， it is important to investigate the temporal and spatial variation of the glacier albedo for simulating the glacier melting. In this study， spatial and temporal variations of albedo were investigated using Landsat images， MODIS daily albedo products and the albedo measured by an Analytical Spectral Device on the Urumqi Glacier No.1 in eastern Tien Shan， China， during May and August， 2016. The data suggested that the spatial distribution of surface albedo was not observed in the early ablation season. However， in the middle or later ablation season， it varied remarkably and generally increased with elevation， especially around the equilibrium line. Temporally， the fluctuation of surface albedo was obvious with from 0.70 to 0.17， a generally decreasing trend was shown. The profile of daily albedo variations was different at various sites on melting glacier surface. The largest daily variation in albedo occurred near the snow line， and followed at the snow sites. A trend of mild fluctuating daily albedo values was shown at ice sites. Most of these variations were induced by the transition in dominant surface type from snow to bare ice， and these transitions in dominant surface type were driven by the air temperature and snowfall. Over bare ice surface， the albedo significantly decreased as the concentrations of surface dust increased， particularly in the visible wavelength. Moreover， the spatial change in surface albedo was related to slope and aspect， because the solar incident angle is dominated by slope and aspect， the surface albedo obviously increases with the solar incident angle on the assumption that the surface condition is uniform.