Estimation the Movement of Glacier in the West of China with ALOS PALSAR and PRISM Data

Glaciers are sensitive indicators of climate fluctuations. The effects of climate warming are for instance evident in the continuous retreat of glaciers. In the paper, the movement of the Dongkemadi Glacier in the Qinhai-Tibetan Plateau and the Keqicar Baxi glacier motion in the Tianshan Mountains of western China are measured using two-pass differential synthetic aperture radar interferometry (InSAR) and feature tracking methods from ALOS PALSAR PRISM data. The movement parameter of the Dongkemadi glacier is resolved using a 46 day-separation ALOS InSAR pair acquired from ascending orbit at Dec. 10, 2007 and Jan. 25, 2008. Although the main potential of two-pass D-InSAR for glacier movement estimation has been shown in several case studies, the decorrelation hinders seriously its application for glaciers motion detection. The amount of “glacier surface” decorrelation is increased by the longer spatial baseline of the interferometric pair, the longer time separation of the SAR images acquisition, more complex terrain, and more noise sources. The longer wavelength SAR data (L-band ALOS) are better to avoid decorrelation phenomenon. Although the L-band ALOS satellite SAR data acquired in winter with 46 days interval, the InSAR pair of ALOS/PALSAR has high correlation and the interferometric fringes are clear, compared with the C-band ASAR data. The results presented these advantages compared to the previous InSAR studies of the mountain glaciers that the correlation is too low to extract the glacier’s movement parameter. We use the ALOS/PALSAR data InSAR pair to extract the motion of the glacier flow, and analyze the glacier flow distribution characteristics in the Dongkemadi Glacier. Feature tracking is an efficient way to derive glacier velocity, which based on a cross-correlation algorithm that seeks offsets of the maximal correlation windows on repeated satellite images. ALOS optical and SAR data in 2007 and 2008 regarding the Keqikaer Baxi glacier are used for the velocity map with feature tracking. In this paper, we also demonstrate that different window sizes lead to different velocities. The Averaged Velocity Gradient (AVG) method is proposed to improve window size in feature tracking and to obtain the most suitable flow field. AVG measures velocity variation between adjacent windows on the whole glacier in the image. Different window sizes lead to different AVG values, and the best-size window corresponds to the value where AVG changes from abrupt to gradual. Using improved feature tracking, two flow fields of the same glacier are acquired with ALOS optical and SAR data respectively. Applicable conditions, accuracy, advantages and disadvantages of the two kinds of data about feature tracking method are discussed. The flow field of the Keqikaer Baxi glacier is obtained from both optical and SAR data. It has been shown on the flow field that velocities increase with the rise in elevation. The Keqikaer Baxi glacier is confirmed to be a dynamic and healthy glacier. Although some differences exist between the two flow fields, our research reveals that they display high levels of correlation and consistency.