Methods and applications of radio frequency geophysics in glaciology

Open Access
Author:
Holschuh, Nicholas Donald
Graduate Program:
Geosciences
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 15, 2016
Committee Members:
  • Richard B Alley, Dissertation Advisor
  • Richard B Alley, Committee Chair
  • Sridhar Anandakrishnan, Committee Member
  • Charles James Ammon, Committee Member
  • Byron Richard Parizek, Outside Member
Keywords:
  • Glaciology
  • Geophysics
  • Radar
  • Antarctica
  • Greenland
Abstract:
Simple radar systems of the past were used primarily for radar depth sounding, the process of using reflection travel times and electromagnetic velocities to determine the ice thickness. Modern radioglaciology uses both the travel times and reflection amplitudes to make inferences about the englacial and subglacial environments; however, non-uniqueness in geophysical data, combined with the large number of physical parameters that control reflection amplitude, have led to significant uncertainties in this type of analysis. In this set of studies, I improve on data collection, processing, and assimilation methods, with a focus on radar reflection amplitudes and internal layers. The first two studies are devoted to radar survey methods, in which I examine the impact of reflector geometry on amplitude (2), and investigate an independent measure of radar attenuation using variable-offset data, in an effort to eliminate the effects of ice chemistry and temperature on reflection amplitudes (3). These studies emphasize the fact that radar data are a product of both the physical system and the imaging process, and caution glaciologists from over-interpreting processing artifacts common in radar data collected in areas of complex glacial flow. In the following two chapters, I go on to provide glaciological applications of processed radar data, interpreting the record of complex flow left behind in englacial reflector slopes (4), and applying improved boundary conditions to better predict the maximum extent of West Antarctic collapse (5). These studies use geometric information from the bed reflector and englacial reflectors to describe the flow regime present in Antarctica today. Chapter 4 examines how boundary conditions that are difficult to observe directly (the geothermal heat flux, as well as the frictional and deformation characteristics of the ice-sheet substrate) manifest through internal layer deformation. Chapter 5 focuses on Marie Byrd Land (MBL), where historically sparse data coverage hindered our ability to project future ice-sheet behavior. I developed a new basal topography for the region, and modeled the collapse state of the West Antarctic Ice Sheet in an effort to determine how much ice can evacuate from the MBL highlands. These chapters motivate the need for more thorough interpretation of the existing radar data, with a focus on better data integration in ice sheet models.