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.

中文翻译：

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从机载雷达图的双折射损失推断冰结构：在西南极洲思韦茨冰川东部剪切边缘的应用

在机载雷达图中，偶尔会观察到起伏的周期性波型，覆盖了传统的放射地层分层，但是，尚需从地球物理或冰川学角度对其进行分析。我们提供了有理论支持的证据，即这些深度周期模式与由于极地冰的双折射引起的接收雷达功率的调制一致，因此表明存在大块织物各向异性。在这里，我们研究了 Thwaites Glacier 东部切变边缘的机载雷达数据中记录的双折射引起的雷达功率的周期性分量，并量化了该边缘的方位角结构强度的横向变化。我们发现跨越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视觉表达，这似乎与当今的冰变形一致。双折射图案的形态以最大剪切位置为中心，并在所有交叉边缘轮廓中观察到，这与冰织物在受到简单剪切时的预测一致。冰川织物在冰流内部显得比在剪切边缘之外更坚固。从非极化雷达图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以及表征极地冰盖变形历史的方法。双折射图案的形态以最大剪切位置为中心，并在所有交叉边缘轮廓中观察到，这与冰织物在受到简单剪切时的预测一致。冰川织物在冰流内部显得比在剪切边缘之外更坚固。从非极化雷达图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以及表征极地冰盖变形历史的方法。双折射图案的形态以最大剪切位置为中心，并在所有交叉边缘轮廓中观察到，这与冰织物在受到简单剪切时的预测一致。冰流内部的冰川结构比剪切边缘的外部更坚固。从非极化雷达图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以及表征极地冰盖变形历史的方法。