Glaciological Interpretation of Changes in Radar Reflection Characteristics from Glaciers

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The speed of glaciers and ice sheets can be affected by hydraulic conditions at their beds. Examples are the dramatic fast-motion of ice streams and glacier surges or the more modest seasonal variations in speed that are common in temperate glaciers. The connection between glacier speed and hydraulic conditions at the bed has been established through borehole and glacial discharge observations. However, these observations yield only very limited spatial coverage (in the case of boreholes) or resolution (in the case of stream discharges). Radio echo-sounding (RES) has been used extensively to map the thickness and structure of many glaciers and ice sheets. The Investigator recently used RES to monitor the spatial and temporal reflection changes within a temperate glacier (Black Rapids Glacier, Alaska) and across a relict ice stream margin in Antarctica. Results from Black Rapids Glacier show distinct temporal changes in RES return characteristics during the early part of the melt season when the speed of the glacier increased significantly. Results from Antarctica show a large spatial change in RES return characteristics; the reflection strength of the bed changed by about 300% in a traverse across the relict margin. Interpretation of the evolving physical conditions at the bed is complicated because some of the observed changes in RES returns from the bed may be caused by changes at the surface and/or within the interior of the ice. Here the investigator proposes to determine the actual changes in reflection characteristics of the bed by using multivariate analysis to remove the effects of transmission through the surface and propagation within the ice. Models of reflection from layered dielectric media will them be used to investigate relationships between the changes in reflection coefficient and changes in basal conditions such as the thickness and electrical conductivity of water at the bed. Their main objective is to use the RES records to gain understanding about physic al conditions at the bed of glaciers and ice sheets.