Basal Conditions of Petermann Glacier and Jakobshavn Isbrae derived from Airborne Ice Penetrating Radar Measurements

Abstract

Understanding ice dynamics and ice basal conditions is important because of their impacts on sea level rise. Radio echo sounding has been extensively used for characterizing the ice sheets. The radar reflectivity of the ice bed is of special importance because it can discriminate frozen and thawed ice beds. The knowledge of the spatial distribution of basal water is crucial in explaining the flow velocity and stability of glaciers and ice sheets. Basal echo reflectivity used to identify the areas of basal melting can be calculated by compensating ice bed power for geometric losses, rough interface losses, system losses and englacial attenuation. Two important outlet glaciers of Greenland, Petermann glacier and Jakobshavn isbrae have been losing a lot of ice mass in recent years, and are therefore studied to derive its basal conditions from airborne radar surveys in this thesis. The ice surface and bed roughness of these glaciers are estimated using Radar Statistical Reconnaissance (RSR) method and validated using roughness derived from NASA’s Airborne Topographic Mapper (ATM) and Ku band altimeter. Englacial attenuation is modeled using Schroeder’s variable attenuation method. After compensating for these losses, the basal reflectivity for the two glaciers is estimated and validated using cross over analysis, geophysics, hydraulic potential, abruptive index and coherence index. The areas of basal melting i.e. areas with higher reflectivity are identified. Petermann glacier is found to have alternate frozen and thawed regions explaining the process of ice movement by friction and freezing. Due to the lack of topographic pinning the glacier is subject to higher ice flow speed. Jakobshavn glacier has several areas of basal melting scattered in the catchment area with most concentration near the glacier front which is likely due to surface water infiltration into ice beds via moulins and sinks. The ice bed channels and retrograde slope of this glacier are also important in routing subglacial water and ice mass. The basal conditions of these two glaciers presented in this study can help in modeling the behavior of these glaciers in the future.