Collaborative Research: Polarimetric Characteristics of Radio-wave Scattering from Water Pathways within Glaciers Deduced by Laboratory Experiments and Computer Simulations

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ABSTRACTMarshallOPP-0520541MatsuokaOPP0520465Intellectual Merits: This is a collaborative proposal by Principal Investigators from the Universities of Washington and Colorado. Water pathways within glaciers transport melt water from the glacier surface to the glacier bed. Water lubricates the bed and introduces significant seasonal and daily variations in ice velocity in mountain glaciers. Current polar ice sheets encounter minor surface melting, but ongoing warming in coastal regions of the ice sheets may change this. If water can get to the bed, significant acceleration of ice flow may occur, which has recently been observed in Greenland. This could ultimately result in rapid fresh-water discharge in the Arctic, significantly contributing to global sea-level rise. Mapping water pathways and their temporal changes is crucial for understanding the spatial and temporal lags between surface melting and bed lubrication events and, more generally, glacier hydrology and mechanics. Remote sensing with ice-penetrating radar is a viable way to investigate temporal and spatial variations of the ice interior. Radar studies can potentially reveal much more than simply the geometry of the bedrock and internal layers. The Principal Investigators will carry out laboratory experiments and computer simulations to investigate how shape, slope, azimuth, dimensions, and contents (air or water) of scatterers within glaciers alter radio-echo intensities as a function of radar frequency and polarization. They will measure scattering from boreholes within an ice cube in a cold room and from thermoplastic polymers that are hanged within an open space. The latter gives an analog of water-filled scatter in glaciers. In each experimental venue, they will examine the bulk scattering from multiple inclusions for various azimuths of the radar-polarization plane relative to the scatterers. Laboratory data will be analyzed in the light of characteristics computed with Discrete Dipole Approximation (DDA). Bulk scattering from multiple cylinders, ellipsoids, and fractures within glaciers will be simulated using DDA, allowing us to examine the ability of radar sounding to explore complex glacier interiors. They will borrow the radar equipment from the U.S. Army Cold Region Research and Engineering Laboratory (CRREL) and use CRREL facilities for the experiments. Broader Impacts: The project will provide research experience for two undergraduate students in both laboratory and theoretical analysis. Second, this research will contribute NSF's overall goals to understand the Arctic environment and its global impact. Third, this project will initiate collaboration between early-career scientists at different institutions. Fourth, this project can complement our ability to infer subsurface characteristics from future polarimetric radar sounding of the Earth, Mars, and other planets.