Dustin M. Schroeder

The Role of Subglacial Hydrology in Ice Sheet Flow and Stability

Thwaites Glacier in the Context of Paleo-Ice-Stream Retreats

Thwaites Glacier is one of the largest, most rapidly changing glaciers on earth with a landward sloping bed that reaches the interior of West Antarctica. Although there are records of melt-water intensive ice-stream retreats on the continental shelf and observations of water driven acceleration in large outlet glaciers, research has focused on the role of ocean-driven melting for Thwaites Glacier. Using radar souding, I compare the configuration of contemporary subglacial bedforms with those of paleo-ice-streams, showing that although prior retreats across regions of crystalline bedrock progressed quickly, Thwaites Glacier is currently grounded in one such region and may be poised for a melt-water intensive retreat.

The Configuration of Subglacial Water Beneath Thwaites Glacier

From an ice flow acceleration perspective, the effect of subglacial water depends on whether the dynamic state of these water bodies is hydrologically distributed or concentrated. The sensitivity of ice flow acceleration and grounding line stability of Thwaites Glacier will depend on the existence, locations, and interconnections of these systems beneath it. Using the specularity of radar echos, I provide the first attenuation-independent characterization of the Thwaites Glacier subglacial water system, which consists of a distributed network of canals feeding a system of concentrated channels. This transition occurs with increasing surface slope, water flux, and basal sheer stress indicating feedback between the ice and water systems.

Information and Uncertainty in Radar Constrained Subglacial Water

Despite the high resolution of along-track focused radar data, the survey of Thwaites Glacier was collected on a 15 km grid and simple interpolation does not accurately represent the observational information and uncertainties in these gaps. Using surface and bed topography with a subglacial water model, I invert radar echo information for a physically consistent interpretation of the water system with more geologically realistic spatial patterns and quantified uncertainties. This approach also provides insight into water depths, conductivity, and geothermal heat flux beneath Thwaites Glacier.

Hypothesis Driven Processing of Ice Sounding Radar Data

Characterizing Subglacial Hydrology with Airborne Radar Sounding

Subglacial water networks are pervasive, dynamic systems that can exert strong control on ice flow. The large spatial extent and thick ice cover of these systems make airborne radar sounding the only practical means of observation, but limited resolution and uncertainties in attenuation losses make traditional ice penetrating analysis techniques insufficient for observing critical processes. By exploiting advances in ice penetrating radar technology and processing, I develop new analysis techniques that quantify the angular distribution of echo energy, constrain the sub-resolution configuration of the bed, and provide an attenuation-independent indicator of subglacial water.

The Development of Ice Penetrating Radar Systems

The HiCARS II Airborne Radar Sounder

The University of Texas Institute for Geophysics (UTIG) collects airborne geophysical data over Arctic and Antarctic ice sheets and glaciers. As a graduate student and member of UTIG field and technical teams, I led the RF development, maintenance, and operation of the new HiCARS II radar system. This system builds on the legacy of the original UTIG HiCARS radar system with coherent acquisition, range-migrated focusing, and linked high-accuracy time stamping. It also adds simultaneously acquired 2MHz radar sounding to the existing 60 MHz system. The migration of primary survey operations to the HiCARS II system in 2011 allowed for improved real-time QC and more robust spares and upgrades with an all UTIG developed system.

Planetary Radar Sounders

Although there are significant theoretical commonalities between airborne and satellite ice penetrating radar systems, the limitations in power, processing, and data volume make radar sounders for planetary exploration a distinct design challenge. As part of the Radar Sounder Working Group for ESA’s Jupiter Icy Moon Explorer mission, I participated in the definition and proposal of a single-frequency ice penetrating radar. The US Europa Science Definition Team (SDT) has studied a mission concept that includes a dual-frequency, multi-channel radar sounder. I led a white paper for the SDT to evaluate the potential for the sounding radar to be used to characterize potential landing sites on Europa.

Antarctic Field Work

The ICECAP Project

The ICECAP Project (Investigation the Cryospheric Evolution of the Central Antarctic Plate) began as a large international airborne geophysical survey of previously underexplored regions of East Antarctica in the international polar year and has grown in to a continuing international collaboration (including the US, the UK, Australia, France, Italy, Germany, Denmark, Chile, and Argentina) with projects spanning the cryosphere. We collect simultaneous dual frequency radar, gravity, magnetic, gps, and scanning-photon-counting-lidar data. As a member of the 08-09, 09-10, and 10-11 ICECAP Antarctic field teams, I served as the lead RF field engineer and radar operator for surveys of the Aurora Subglacial Basin, Byrd Glacier, and Astrolabe Glacier.