岗纳楼冰川表面流速时空变化特征提取及分析

Extraction and Analysis of Temporal-Spatial Variation Characteristics of Surface Velocity of the Gangnalou Glacier

冰川表面流速是反映冰川动态变化的重要指标,能够为冰川物质平衡提供重要信息。利用2016年的13景Sentinel-1A影像和合成孔径雷达(synthetic aperture radar,SAR)偏移量追踪法测定岗纳楼冰川表面流速场,并根据地表温度是否大于0℃将其分为冰封期(10月-次年3月)和消融期(4月-9月)。其中,冰封期流速场较为稳定,中轴流速快于两侧,边界流速趋于0 m/a;消融期流速场冰舌中下部与冰舌上部差异明显,冰川表面流速具有分区特征。基于SAR观测数据,在冰川积累增厚、消融减薄及冰川表面流动的综合影响下,冰封期冰川表面流速最大为65.43 m/a;消融期冰川表面流速最大为46.28 m/a。通过分析冰川中线流速、冰面高程以及地表温度之间的关系可知,冰封期内,岩床坡度是影响冰川流速的主要原因,且岗纳楼冰川为"压缩-舒张"流运动模式;消融期内,地表温度升高、冰面海拔变化是冰川表面流速出现分区现象的主要原因。

Objectives:The temporal-spatial variation characteristic of the glacier surface velocity is an important indicator of dynamic change of glacier and can provide important information for glacier mass balance. Surface temperature, glacier bed slope and glacier altitude are all important factors that affect glacier surface velocity, and their respective effects need to be analyzed.Methods: In this paper, the offsettracking method was used to measure the surface velocity of the Gangnalou Glacier, based on high-resolution Sentinel-1 A synthetic aperture radar(SAR) images ranging from January 2016 to December 2016. We divided the surface velocity into freezing period and ablation period based on whether surface temperature was greater than 0℃ or not. For further analysis, we extracted the central line glacier velocity, and then jointly used surface temperature and digital elevation model(DEM) to analyze the influences of temperature and glacier bed slope.Results: The results showed that surface velocity of freezing period was more stable and central line glacier velocity was faster than that of boundary which tended to 0 m/a. SAR measurements were affected by glacier ablation, accumulation and motion, and showed that the maximum surface velocity was 65.43 m/a during freezing period and 46.28 m/a during ablation period. This surface velocity field showed a partitioning phenomenon in which the velocities of the middle and lower parts of glacier tongue were significantly different from that of the upper part during ablation period.Conclusions: The surface velocity of the Gangnalou Glacier was affected by many complex factors, of which glacier ablation and glacier bed slope are main factors. The partitioning phenomenon in the ablation period could be better explained by increasing surface temperature and changing glacier altitude, which directly affected glacier ablation and accumulation. Additionally, by analyzing the effect of the glacier bed slope, we found that the Gangnalou Glacier followed the compressive and extending flow mode in the freezing period.