Glaciological Interpretation of Changes in Radar Reflection Characteristics from Glaciers

冰川雷达反射特征变化的冰川学解释

• 批准号: 9530827
• 负责人: Charles Raymond
• 金额: $ 3.75万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-07-01 至 1998-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9530827&HistoricalAwards=false
• 关键词: Glaciological; Interpretation; Changes; Radar; Reflection

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.

冰川和冰盖的速度会受到河床水力条件的影响。 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速度的较温和的季节性变化。 冰川速度和水力条件之间的联系，在床已建立通过钻孔和冰川流量观测。 然而，这些观测只产生非常有限的空间覆盖范围（在钻孔的情况下）或分辨率（在河流排放的情况下）。 无线电回声探测已被广泛用于测绘许多冰川和冰盖的厚度和结构。 调查员最近使用RES监测的空间和时间的反射变化内的温带冰川（黑急流冰川，阿拉斯加），并在南极洲的残余冰流边缘。 从黑急流冰川的结果表明，在RES返回特性的明显的时间变化在融化季节的早期，当冰川的速度显着增加。南极洲的结果表明RES返回特性的空间变化很大，在穿越残留边缘的导线中，床层的反射强度变化约300%。 解释不断变化的物理条件在床上是复杂的，因为一些观察到的变化RES返回从床上可能是由表面和/或内部的冰的变化。 在这里，研究人员提出，以确定实际的变化，反射特性的床，通过使用多变量分析，以消除通过表面和传播内的冰的传输的影响。 分层电介质的反射模型将被用来研究反射系数的变化与基础条件的变化之间的关系，例如床中水的厚度和电导率。 他们的主要目标是利用RES记录来了解冰川和冰盖床的气候条件。