Inferring Ice Fabric From Birefringence Loss in Airborne Radargrams: Application to the Eastern Shear Margin of Thwaites Glacier, West Antarctica
Inferring Ice Fabric From Birefringence Loss in Airborne Radargrams: Application to the Eastern Shear Margin of Thwaites Glacier, West Antarctica
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从机载雷达图中的双折射损失推断冰结构：在南极洲西部思韦茨冰川东部剪切边缘的应用
DOI：
10.1029/2020jf006023
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Bienert, N. L.
中科院分区：
文献类型：
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作者：
Young, T. J.;Schroeder, D. M.;Jordan, T. M.;Christoffersen, P.;Tulaczyk, S. M.;Culberg, R.;Bienert, N. L.
在航空雷达图中，偶尔会观察到覆盖传统放射性地层分层的波动周期性振幅模式，然而，它们尚未从地球物理或冰川学的角度进行分析。我们提出了理论支持的证据，这些深度周期性图案与由于极地冰的双折射引起的接收到的雷达功率的调制一致，因此表明存在块状结构各向异性。在这里，我们调查的双折射引起的雷达功率的周期性组成部分记录在机载雷达数据在东剪切边缘的思韦茨冰川和量化的横向变化在这个边缘的方位角组构强度。我们发现穿过剪切边缘的双折射周期性的深度变化是其剪切状态及其发展的直观表达，这似乎与当今的冰变形一致。双折射图案的形态集中在最大剪切的位置，并在所有跨边缘剖面中观察到，与受到简单剪切时冰组构的预测一致。冰流内部的冰内组构比剪切边缘外部的冰内组构更强。从非偏振雷达图中检测双折射周期性提出了一种新的使用地下雷达来约束结构强度的横向变化，定位当前和过去的剪切边缘，并表征极地冰盖的变形历史。
In airborne radargrams, undulating periodic patterns in amplitude that overprint traditional radiostratigraphic layering are occasionally observed, however, they have yet to be analyzed from a geophysical or glaciological perspective. We present evidence supported by theory that these depth‐periodic patterns are consistent with a modulation of the received radar power due to the birefringence of polar ice, and therefore indicate the presence of bulk fabric anisotropy. Here, we investigate the periodic component of birefringence‐induced radar power recorded in airborne radar data at the eastern shear margin of Thwaites Glacier and quantify the lateral variation in azimuthal fabric strength across this margin. We find the depth variability of birefringence periodicity crossing the shear margin to be a visual expression of its shear state and its development, which appears consistent with present‐day ice deformation. The morphology of the birefringent patterns is centered at the location of maximum shear and observed in all cross‐margin profiles, consistent with predictions of ice fabric when subjected to simple shear. The englacial fabric appears stronger inside the ice stream than outward of the shear margin. The detection of birefringent periodicity from non‐polarimetric radargrams presents a novel use of subsurface radar to constrain lateral variations in fabric strength, locate present and past shear margins, and characterize the deformation history of polar ice sheets.