Estimating Glacier Ice Thickness and Mass Balance Using Multiple Spaceborne Geodetic Techniques
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The melting of glaciers and ice caps makes a significant contribution to present-day sea level rise. Recently, multiple space-borne remote sensing techniques have been successfully used to obtain geodetic observations, which were used to estimate the contribution of global glacier melt to sea level rise. However, estimates from different approaches yield large discrepancies in certain glacierized areas such as the Eastern Nyainqen Tanglha. Moreover, other glacierized regions such as the Novaya Zemlya in the Russian Arctic have been under-studied. Therefore, to characterize and quantify accurate glacier mass balance estimates over Eastern Nyainqen Tanglha and Novaya Zemlya, an iterative velocity-based method is proposed to estimate glacier thickness. First, a new iterative method is presented, which estimates ice thickness using surface velocity and surface topography. The temperature-related rate factor for temperate glaciers is empirically obtained based on multiple in-situ measurements, while the rate factor for non-temperate glaciers follows the assumption made by previous studies. A validation was performed with 15 previous methods over 8 glaciers. Based on the comparative results, the proposed method in glacierized areas where direct observations are limited is promising. Second, multiple traditional spaceborne techniques for observing surface mass balance were tested in the Novaya Zemlya. The mass variation trend was obtained based on observations from Gravity Recovery and Climate Experiment (GRACE) and radar altimeter over 4 selected glaciers. The glacier outflow and influx were also determined using surface velocity and snowfall observations. Additionally, the contributions of outflow and influx to mass change for Novaya Zemlya were identified. Finally, the proposed thickness estimate method is applied to 4 largest glaciers in Nyainqen Tanglha. Surface velocity estimates were calculated from Advanced Land Observing Satellite (ALOS)/ALOS-2 Phased Array type L-band SAR (PALSAR) image pairs via speckle matching. Surface slope distribution was calculated from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Digital Elevation Model (DEM) data. Consequently, the thickness distribution map from 2008 to 2016 was obtained. Furthermore, the mass balance and thickness changes were determined. These estimates have an agreement with previous ones from GRACE and ASTER DEM differencing approaches.