Crystal orientation fabrics within the Antarctic ice sheet revealed by a multipolarization plane and dual-frequency radar survey
Crystal orientation fabrics within the Antarctic ice sheet revealed by a multipolarization plane and dual-frequency radar survey
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DOI：
10.1029/2003jb002425
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发表时间：
2003-10-24
影响因子：
3.9
通讯作者：
Watanabe, O
中科院分区：
文献类型：
--
作者：
Matsuoka, K;Furukawa, T;Watanabe, O
为了研究晶体取向结构（COF）引起的冰盖黏度结构，我们在南极洲东部进行了多极化平面和双频雷达测量。从富士圆顶到海岸的670公里长的流水线和300公里和20公里长的两条横线分别进行了雷达测量。在接近出入口冰川的收敛冰流扇区下游约40 ~ 60%的冰深范围内，雷达回波高度依赖于极化面。极化方向垂直于冰流时，回波强度比极化方向平行于冰流时强约10 dB。这个特征在这个汇聚流扇区的上部并不明显。在更远的内陆，在冰流发散或平行的地方，由于雷达极化的变化，雷达回波变化了几个分贝，并且在两个方向上都有最大值。双频数据表明，反射的原因是COF的变化。多极化数据表明，各向异性反射和双折射分别是引起下游和上游雷达回波各向异性的原因。通过基于冰芯的COF研究，我们发现，在下游，冰是由单极和垂直带状织物堆叠而成的。相反，我们认为单极簇的变化导致了上游各向同性反射率的变化。我们还讨论了冰流COF的发展及其对冰盖动力学的意义。
[1] To investigate the viscosity structure of ice sheets induced by crystal orientation fabric (COF), we carried out a multipolarization plane and dual-frequency radar survey in East Antarctica. Radar surveys were done along a 670-km-long flow line from Dome Fuji toward the coast and two transverse lines of 300-km and 20-km length, respectively. The radar echoes were highly dependent on the polarization plane for ice depths between about 40 and 60% of the ice thickness in the lower reaches of the convergent ice flow sector approaching the outlet glacier. When the polarization was perpendicular to the ice flow, echoes were about 10 dB stronger than when the polarization was parallel to the ice flow. This feature was not clear in the upper part of this convergent flow sector. Farther inland, where ice flow is divergent or parallel, the radar echo varied by several decibels because of changes of the radar polarization and had maxima in two orientations. Dual-frequency data showed that the cause of the reflections was changes in COF. Multipolarization data identified anisotropic reflectivities and birefringence as causes of the anisotropic radar echoes in the lower and upper reaches, respectively. With the aid of ice-core-based studies on COF, we show that ice is composed of stacked layers of single-pole and vertical girdle fabrics in the lower reaches. In contrast, we argue that changes of single-pole clustering cause isotropic reflectivities in the upper reaches. We also discuss on the development of COF along ice flow and its implication to ice sheet dynamics.