Self-affine subglacial roughness: consequences for radar scattering and basal water discrimination in northern Greenland
Self-affine subglacial roughness: consequences for radar scattering and basal water discrimination in northern Greenland
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DOI：
10.5194/tc-11-1247-2017
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发表时间：
2017-05
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影响因子：
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通讯作者：
T. Jordan;M. Cooper;D. Schroeder;Christopher B. Williams;J. Paden;M. Siegert;J. Bamber
中科院分区：
文献类型：
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作者：
T. Jordan;M. Cooper;D. Schroeder;Christopher B. Williams;J. Paden;M. Siegert;J. Bamber
摘要。从无线电回波探测（RES）数据中，可以通过地形的统计分析或从基底雷达散射推断，在多种长度尺度上确定冰下粗糙度。以往的研究表明，冰下地形呈现出自仿射（幂律）粗糙度标度行为，但现有的雷达散射模型并未考虑到这一点。在此，利用来自格陵兰岛北部的RES数据，我们引入了一个自仿射统计框架，该框架能够将地形尺度的粗糙度与雷达散射的电磁理论进行一致的整合。我们证明，使用波形突变度（脉冲尖峰度）量化的雷达散射程度在地形上受赫斯特（粗糙度幂律）指数控制。值得注意的是，镜面床反射与较低的赫斯特指数相关，漫散射与较高的赫斯特指数相关。突变波形（镜面反射）先前已被用作基底水的RES诊断依据，为了检验这一假设，我们将我们的雷达散射图与近期对基底热状态的预测进行了比较。我们证明，大多数融化区域（高于压力熔点）呈现出漫散射特征，这与先前的方法相矛盾。自仿射统计为冰下地形提供了一个通用模型，可以提高我们对基底特性与冰盖动力学之间关系的理解。
Abstract. Subglacial roughness can be determined at a variety of length scales from radio-echo sounding (RES) data either via statistical analysis of topography or inferred from basal radar scattering. Past studies have demonstrated that subglacial terrain exhibits self-affine (power law) roughness scaling behaviour, but existing radar scattering models do not take this into account. Here, using RES data from northern Greenland, we introduce a self-affine statistical framework that enables a consistent integration of topographic-scale roughness with the electromagnetic theory of radar scattering. We demonstrate that the degree of radar scattering, quantified using the waveform abruptness (pulse peakiness), is topographically controlled by the Hurst (roughness power law) exponent. Notably, specular bed reflections are associated with a lower Hurst exponent, with diffuse scattering associated with a higher Hurst exponent. Abrupt waveforms (specular reflections) have previously been used as a RES diagnostic for basal water, and to test this assumption we compare our radar scattering map with a recent prediction for the basal thermal state. We demonstrate that the majority of thawed regions (above pressure melting point) exhibit a diffuse scattering signature, which is in contradiction to the prior approach. Self-affine statistics provide a generalised model for subglacial terrain and can improve our understanding of the relationship between basal properties and ice-sheet dynamics.