Conference Agenda

In contrast to the glacier mass losses observed at other locations around the world, some glaciers in the High Mountains of Asia appear to have gained mass in recent decades, which was called as ‘Karakoram anomaly’ or ‘Karakoram-Pamir anomaly’. Recent study to laser altimetry data found the centre of the anomaly might locates at the West Kunlun instead of the Karakoram. We performed differential interferometry to 14 pairs of bistatic TerraSAR-X and TanDEM-X observed the West Kunlun and its surroundings obtained at ~2013 by referring to SRTM observed in 2000. After removing seasonal effect and penetration depth differences, it found during 2000 and 2013, glacier mass balance rate at the West Kunlun was 0.128 ± 0.055 m w.e.a^-1 and most of its surrounding area also experienced a mass gain that varied from 0.043 to 0.363 m w.e.a^-1, with a decreasing gradient from northeast to southwest. At southwest of this study region, glacier presented significant mass lost at -0.286 ± 0.067 m w.e.a^-1. For the West Kunlun region, northern slope gained mass quicker than southern slope, eastern and western part gained mass quicker than central part. Comparing to previous studies applied ICESat satellite laser altimetry data, similar results of glacier height changing was obtained at their footprints. Our results suggested a decreasing gradient of glacier mass balance from the Upper Tarim edge to the Karakoram, which is similar to previous ICESat derived gradient rather than topographic difference results derived with SPOT/HRS and SRTM. Glacier surging was common at the West Kunlun. Surging and quiescent glaciers identified by glacier height changing pattern was almost the same to previous study derived with feature tracking. They cover almost one third of the total glacierized region. For the West Kunlun, glacier height changes in different elevation bins for non-surging glaciers present significant and homogeneous height increasing above 5450 m, while below 5400 glaciers shows significant thinning, which indicate the warming and moisturizing trend in the centre of the anomaly area.

Glacier is one of the most important climate change indicators in both regional and global scale. High Mountain Asia has the largest extend of glacier outside the polar region. As the Asian Water Tower, glacier in this region also has distinct ecological significance due to its vast water source. Its movement has close correlation with the risk of glacier lake outburst in highland. As a consequence, glacier dynamics in High Mountain Asia including mass balance, surface velocity and outline detection have been research hotspot. In recent years, synthetic aperture radar (SAR) observation has been regarded as an effective tool for glacier surface motion monitoring with wide range and high resolution. Therefore, it is essential to employ SAR observation to evaluate the velocity of glaciers in Tibet, China, which may be the basis for glacier dynamics and even climate change conditions in High Mountain Asia region.

SAR echo records both amplitude and phase information. From one aspect, the phase-based traditional differential SAR interferometry (D-InSAR) can achieve a millimeter accuracy in deformation detection theoretically while its application to glacier dynamics is generally limited by decorrelation. From another aspect, the intensity-based pixel offset tracking (POT), taking advantages of the intensity from backscatter signals, can implement large displacement in both range and azimuth direction whereas redundancy and error estimation in matching decorrelated patches arises in the calculation procedure. Hence an integrated method combining these two complements is applied to sub-region in High Mountain Asia in exploring glacier dynamics which can improve utilization of SAR observation.

In this study, acquisitions from Sentinel-1A and Sentinel-1B constitutes the data stack with a 6-day temporal baseline. Qualitative and quantitative evaluations of the glacier velocity are made for understanding the surface motion and glacier dynamics. Compared with other space-borne SAR acquisitions, the C-band Sentinel-1 data have smaller temporal decorrelation effects with shorter revisit time, which might be attributed to the good interferometry analysis.