Browsing by Author "Adams, Ed"

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Characterizing sub-glacial hydrology using radar simulations
(Copernicus GmbH, 2024-04) Pierce, Chris; Gerekos, Christopher; Skidmore, Mark; Beem, Lucas; Blankenship, Don; Sang Lee, Won; Adams, Ed; Lee, Choon-Ki; Stutz, Jamey
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. Through multiple simulations comparing various water system geometries, such as canals and sub-glacial lakes, we demonstrated the important role that topography and water geometry can play in observed RES reflectivity. From the scenarios that we tested, we concluded the bright reflector from our RES flight line cannot be a Röthlisberger channel but could be consistent with a series of flat canals or a sub-glacial lake. However, we note our simulations were not exhaustive of all possible sub-glacial water configurations. The approach outlined here has broad applicability for studying the basal environment of large glaciers. We expect to apply this technique when constraining the geometry and extent of many sub-glacial hydrologic structures in the future. Further research may also include comprehensive investigations of the impact of sub-glacial roughness, substrate heterogeneity, and computational efficiencies enabling more complex and complete simulations.
Exploring canyons beneath Devon Ice Cap for sub-glacial drainage using radar and thermodynamic modeling
(Cambridge University Press, 2024-09) Pierce, Chris; Skidmore, Mark; Beem, Lucas; Blankenship, Don; Adams, Ed; Gerekos, Christopher
Sub-glacial canyon features up to 580 m deep between flat terraces were identified beneath Devon Ice Cap during a 2023 radar echo sounding (RES) survey. The largest canyon connects a hypothesized brine network near the Devon Ice Cap summit with the marine-terminating Sverdrup outlet glacier. This canyon represents a probable drainage route for the hypothesized water system. Radar bed reflectivity is consistently 30 dB lower along the canyon floor than on the terraces, contradicting the signature expected for sub-glacial water. We compare these data with backscattering simulations to demonstrate that the reflectivity pattern may be topographically induced. Our simulated results indicated a 10 m wide canal-like water feature is unlikely along the canyon floor, but smaller features may be difficult to detect via RES. We calculated basal temperature profiles using a 2D finite difference method and found the floor may be up to 18°C warmer than the terraces. However, temperatures remain below the pressure melting point, and there is limited evidence that the canyon floor supports a connected drainage system between the DIC summit and Sverdrup Glacier. The terrain beneath Devon Ice Cap demonstrates limitations for RES. Future studies should evaluate additional correction methods near complex terrain, such as RES simulation as we demonstrate here.
Modeling Snow Temperature in Complex Topography
(2013-03) Glatz, Patricia; Adams, Ed
The stability of snow on a mountain slope is largely dependent on particular states of snow layers. This includes the morphologic state of snow cover at the microstructure level, e.g. bonds and grains. Microstructure is largely dependent on the surface temperature and the temperature gradient of snow after its initial formation as atmospheric precipitation. These thermal variations at and near the surface may lead to morphologies such as ice crusts, surface hoar, and near surface recrystallization. [1] To look at this relationship, the first principles energy balance model RadThermRT has been enhanced and implemented to account for the complex nature of the topography of a given slope. From the geographic data and weather input, one dimensional finite difference heat conduction equations are solved normal to the surface of interest, which allows the temperature profile of each facet to be determined. Currently, two slopes in the Yellowstone Club are being modeled with others in progress to see if these weak spots can be pre-casted. To date, surface crystallization can be modeled and seen for days that are known to have crystallization.