Glaciological Interpretation of Changes in Radar Reflection Characteristics from Glaciers

冰川和冰原的速度会受到其床上的水力条件的影响。例如，冰流和冰川涌动的剧烈快速运动，或者在温带冰川中常见的较为温和的速度季节性变化。通过钻孔和冰川流量观测，建立了冰川速度与河床水力条件之间的联系。然而，这些观测只产生非常有限的空间覆盖（在钻孔的情况下）或分辨率（在溪流排放的情况下）。无线电回声测深（RES）已广泛用于绘制许多冰川和冰盖的厚度和结构。研究者最近使用RES监测了温带冰川（阿拉斯加黑急流冰川）和南极洲残冰流边缘的时空反射变化。黑急流冰川在融冰期前期，冰川速度显著加快，RES回归特征随时间变化明显。南极地区RES回归特征空间变化较大；在沿残余边缘的一次穿越中，床层的反射强度变化了约300%。对床上不断变化的物理条件的解释是复杂的，因为从床上观测到的RES返回的一些变化可能是由冰表面和/或冰内部的变化引起的。在这里，研究者建议通过使用多变量分析来确定床反射特性的实际变化，以消除通过表面传播和在冰内传播的影响。层状介质的反射模型将用于研究反射系数的变化与基础条件（如床层水的厚度和电导率）变化之间的关系。他们的主要目标是利用RES记录来了解冰川和冰盖床的物理状况。

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.