Potential mechanisms for anisotropy in ice-penetrating radar data
Potential mechanisms for anisotropy in ice-penetrating radar data
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DOI：
10.3189/2012jog11j114
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发表时间：
2012
影响因子：
3.4
通讯作者：
R. Drews;O. Eisen;D. Steinhage;I. Weikusat;S. Kipfstuhl;F. Wilhelms
中科院分区：
文献类型：
--
作者：
R. Drews;O. Eisen;D. Steinhage;I. Weikusat;S. Kipfstuhl;F. Wilhelms
摘要：在 Dronning Maud Land EPICA 深钻站点附近的南极高原上收集的雷达数据（中心频率 150 MHz）的后向散射功率发生系统变化，具体取决于方位角天线方向。反向散射极值与表面应变率的主方向一致，并随深度变化。在 900 m 上方，当天线极化与最大压缩方向对齐时，后向散射最强，而在 900 m 以下，最大偏移 90°，指向侧流膨胀。我们使用不同的散射模型并结合冰芯数据研究了细长气泡和垂直变化的晶体取向结构（COF）的反向散射。我们假设 COF 的短尺度变化是观测到的各向异性的主要机制，并且两个区域之间的 900 m 边界是由杂质含量不同的冰引起的。这种观测可以推断 COF 随深度的变化，并且也可能适合绘制全新世和冰川冰之间的过渡图。
Abstract Radar data (center frequency 150 MHz) collected on the Antarctic plateau near the EPICA deep-drilling site in Dronning Maud Land vary systematically in backscattered power, depending on the azimuth antenna orientation. Backscatter extrema are aligned with the principal directions of surface strain rates and change with depth. In the upper 900m, backscatter is strongest when the antenna polarization is aligned in the direction of maximal compression, while below 900 m the maxima shift by 90° pointing towards the lateral flow dilatation. We investigate the backscatter from elongated air bubbles and a vertically varying crystal-orientation fabric (COF) using different scattering models in combination with ice-core data. We hypothesize that short-scale variations in COF are the primary mechanism for the observed anisotropy, and the 900 m boundary between the two regimes is caused by ice with varying impurity content. Observations of this kind allow the deduction of COF variations with depth and are potentially also suited to map the transition between Holocene and glacial ice.