Investigating the internal structure of glaciers and ice sheets using Ground Penetrating Radar

• Main Author: Delf, Richard John
• Other Authors: Bingham, Robert, Giannopoulos, Antonios, Curtis, Andrew, Nienow, Peter, Natural Environment Research Council (NERC)
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Edinburgh 2021
• Subjects: glaciology; geophysics; ice penetrating radar; glacier flow modelling; Svalbard; Von Postbreen; glacier; Ice Sheet
• Online Access: https://hdl.handle.net/1842/38123; https://doi.org/10.7488/era/1392

Ice penetrating radar (IPR) is a key tool in understanding the internal geometry and nature of glaciers and ice sheets, and has widely been used to derive bed topography, map internal layers and understand the thermal state of the cryosphere. Modern glacier and ice-sheet models facilitate increased assimilation of observations of englacial structure, including glacier thermal state and internal-layer geometry, yet the products available from radar surveys are often under-utilised. This thesis presents the development and assessment of radar processing strategies to improve quantitative retrievals from commonly acquired radar data. The first major focus of this thesis centres on deriving englacial velocities from zero-offset IPR data. Water held within micro- and macro-scale pores in ice has a direct influence on radar velocity, and significantly reduces ice viscosity and hence impacts the long-term evolution of polythermal glaciers. Knowledge of the radar velocity field is essential to retrieve correct bed topography from depth conversion processing, yet bed topography is often estimated assuming constant velocity, and potential errors from lateral variations in the velocity field are neglected. Here I calculate the englacial radar velocity field from common offset IPR data collected on Von Postbreen, a polythermal glacier in Svalbard. I first extract the diffracted wavefield using local coherent stacking, then use the focusing metric of negative entropy to deduce a local migration velocity field from constant-velocity migration panels and produce a glacier-wide model of local radar velocity. I show that this velocity field is successful in differentiating between areas of cold and temperate ice and can detect lateral variations in radar velocity close to the glacier bed. The effects of this velocity field in both migration and depth-conversion of the bed reflection are shown to result in consistently lower ice depths across the glacier, indicating that diffraction focusing and velocity estimation are crucial in ...