Characterizing sub-glacial hydrology using radar simulations

• Published in: The Cryosphere
• Main Authors: Pierce, Chris, Gerekos, Christopher, Skidmore, Mark, Beem, Lucas, Blankenship, Don, Lee, Won Sang, Adams, Ed, Lee, Choon-Ki, Stutz, Jamey
• Format: Text
• Language: English
• Published: 2024
• Subjects: Antarc*; Antarctic; Thwaites Glacier
• Online Access: https://doi.org/10.5194/tc-18-1495-2024; https://tc.copernicus.org/articles/18/1495/2024/

The structure and distribution of sub-glacial water directly influences Antarctic ice mass loss by reducing or enhancing basal shear stress and accelerating grounding line retreat. A common technique for detecting sub-glacial water involves analyzing the spatial variation in reflectivity from an airborne radar echo sounding (RES) survey. Basic RES analysis exploits the high dielectric contrast between water and most other substrate materials, where a reflectivity increase ≥ 15 dB is frequently correlated with the presence of sub-glacial water. There are surprisingly few additional tools to further characterize the size, shape, or extent of hydrological systems beneath large ice masses. We adapted an existing radar backscattering simulator to model RES reflections from sub-glacial water structures using the University of Texas Institute for Geophysics (UTIG) Multifrequency Airborne Radar Sounder with Full-phase Assessment (MARFA) instrument. Our series of hypothetical simulation cases modeled water structures from 5 to 50 m wide, surrounded by bed materials of varying roughness. We compared the relative reflectivity from rounded Röthlisberger channels and specular flat canals, showing both types of channels exhibit a positive correlation between size and reflectivity. Large ( > 20 m ), flat canals can increase reflectivity by more than 20 dB , while equivalent Röthlisberger channels show only modest reflectivity gains of 8–13 dB . Changes in substrate roughness may also alter observed reflectivity by 3–6 dB . All of these results indicate that a sophisticated approach to RES interpretation can be useful in constraining the size and shape of sub-glacial water features. However, a highly nuanced treatment of the geometric context is necessary. Finally, we compared simulated outputs to actual reflectivity from a single RES flight line collected over Thwaites Glacier in 2022. The flight line crosses a previously proposed Röthlisberger channel route, with an obvious bright bed reflection in the radargram. ...