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

  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 offset-tracking method was used to measure the surface velocity of the Gangnalou Glacier, based on high-resolution Sentinel-1A 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.