利用Landsat 8和TerraSAR-X影像研究老虎沟12号冰川运动特征

Monitoring displacement of Laohugou glacier No.12 based on Landsat 8 and TerraSAR-X images

采用归一化互相关算法精确配准Landsat 8影像得到了2014年—2016年不同季节冰川的运动速率,并利用其热红外波段对不同时刻的地表温度进行反演;通过强度追踪法处理TerraSAR-X影像得到了2008年4月—10月不同时段的冰川运动速率。两种数据得到的结果表明:冰川末端流速较小,中部流速增大,流速从轴部向两侧递减;冬季流速明显小于夏季,变化趋势与温度变化具有一致性。冰川西侧分支的移动速率相对较大,从Landsat 8和TerraSAR-X提取的最大速率分别为2.56 m·d^(-1)和2.74 m·d^(-1)。最后对稳定区域的冰川流速进行统计,结果显示Landsat 8提取的冰川流速精度控制在1—9 cm d^(-1),基于TerraSAR-X的强度追踪法提取移动速率的精度控制在2cm·d^(-1),验证了两种数据监测冰川移动的可靠性。

The flow velocity of a glacier is not uniform in time and space. Thus, the flow characteristics of glaciers should be detected to fully monitor their situation through satellite images. In this study, we use the Normalized Cross Correlation （NCC） algorithm and the intensity tracking method to study the spatial distribution characteristics of Laohugou glacier No. 12 in Gansu province, to explore the relationship between glacier flow velocity and temperature, and to evaluate error sources and precision using Landsat 8 and SAR images. The flow velocities of different seasons between 2014 and 2016 are obtained from Landsat 8 images in the NCC registration algorithm. The land surface temperature is inversed from the TIRS band. Flow velocities from April to October 2008 are retrieved from TerraSAR-X images under an intensity tracking method. Results of the two types of data show that the velocity at the glacier terminal is lower than that in the central area and that it decreases from the axis to both sides. Flow velocity is faster in summer than in winter, and its trend is consistent with temperature changes. Moreover, the velocity at the west branch is relatively large, and the maximum velocities extracted from Landsat 8 and TerraSAR-X are 2.56 m·d^-1 and 2.74 m·d^-1, respectively. Finally, the reliability of monitoring glacier flow based on the two types of data is demonstrated by using the mean and standard deviation in the stable zones. Considering these values, we find that the velocity accuracy for Landsat 8 is between 1 and 9 cm·d^-1 and that it is better than the other type of data by approximately 2 cm·d^-1. Our methods can effectively monitor glacier flow conditions, and reliability evaluation shows that the velocity accuracy is up to several centimeters per day. The comparisons indicate that radar images are especially sensitive to surface deformation due to their high spatial resolution. The SNR of optical images is also relatively high to improve integrity. Therefore, the two types of data can be used in combination to extract glacier flow information comprehensively.