Radio-frequency attenuation beneath Siple Dome,West Antarctica, from wide-angle and profiling radar observations
Radio-frequency attenuation beneath Siple Dome,West Antarctica, from wide-angle and profiling radar observations
复制标题
来自广角和剖面雷达观测的西南极洲 Siple Dome 下方的射频衰减
作者：
D. Winebrenner;Ben E. Smith;G. Catania;H. Conway;C. Raymond
摘要冰床润滑状态的空间分布，即冻结与潮湿条件下的知识，是理解冰盖流动的关键。雷达探测可以探测湿床和冻床之间不同的反射率，但受到冰床回波衰减不确定性的限制。在这里，我们提出了两种方法来估计衰减：（1）广角雷达探测，其中源和接收器的位置是不同的，以改变传播路径长度，从而回波幅度;（2）剖面，其中通过不同的冰厚度（假设恒定的床反射率）探测获得类似的变化。西南极洲的Siple Dome为这些方法的应用提供了异常有利的环境：Siple Dome下面的床是平坦的，雷达反射率均匀，而冰的厚度变化了几百米。宽角度数据4公里的首脑会议产生的估计特征衰减长度为124米（35分贝公里-1损失），而剖析产生的估计为168米。估计之间的差异是适度的范围内的衰减长度相比，在文献中报道。尽管如此，通过对两种冰特性的影响进行界定，可以证明这一方法是有用的，这两种方法对这两种冰特性的反应是不同的：（1）广角探测法在峰顶下面取样的是相对温暖的（有损耗的）冰，而剖面法在侧翼下面也取样的是相对寒冷的冰;以及（2）冰中应变诱导的晶体取向组构和由此产生的介电各向异性将从顶部到侧面变化，并且可能比剖面测量更强烈地影响广角探测。
Abstract Knowledge of the spatial distribution of bed lubrication regimes, i.e. frozen vs wet conditions, is crucial for understanding ice-sheet flow. Radar sounding can probe differing reflectivities between wet and frozen beds, but is limited by uncertainty in attenuation within the ice of bed echoes. Here we present two methods to estimate attenuation: (1) wide-angle radar sounding, in which source and receiver locations are varied so as to vary propagation path length, and thus echo amplitude; and (2) profiling, inwhich similar variations are obtained by sounding through varying ice thicknesses (assuming constant bed reflectivity). Siple Dome, West Antarctica, provides unusually favorable circumstances for application of these methods: the bed beneath Siple Dome is flat and uniform in its radar reflectivity, while ice thickness varies by several hundred meters. Wide-angle data 4 km from the summit yield an estimate for characteristic attenuation length of 124 m (35 dB km–1 loss), whereas profiling yields an estimate of 168 m.The difference between estimates is modest compared to the range of attenuation lengths reported in the literature. It may nonetheless prove informative by bounding effects of two ice properties to which the methods respond differently: (1) wide-angle sounding sampled relatively warm (lossy) ice beneath the summit, whereas the profiling method sampled relatively cold ice beneath the flanks as well; and (2) strain-induced crystal orientation fabrics and resulting dielectric anisotropy in the ice would vary from summit to flank, and may influence wide-angle sounding more strongly than profiling.