线性沙丘和大尺度沙丘的Radar散射：对土卫六的应用
Radar scattering of linear dunes and mega-yardangs: Application to Titan
摘要：
卡西尼-惠更斯号航天器上的Ku波段（13.8 GHz - 2.2 cm）雷达仪器揭示了土卫六表面的丰富性，因为发现了许多海洋、湖泊、河流、低温火山流和广阔的沙丘。线形沙丘是土卫六上的一个主要地貌特征，覆盖了土卫六表面的17%，主要分布在赤道地区。然而，雷达仪器的分辨率不够好，无法对这些特征的形态进行详细研究。此外，其他与风有关的线性地貌，如巨型雅丹（在粘性岩石中形成的线性风蚀山脊），可能会呈现出类似的雷达特征，可能会与沙丘混淆。我们进行了比较研究的线性沙丘和mega-yardangs的雷达辐射，基于代表性的陆地类似物：位于埃及西部的大沙海和纳米比亚的纳米布沙漠的线性沙丘，以及在伊朗东部的卢特沙漠和乍得北部的博尔库沙漠观察到的mega-yardangs。我们利用TerraSAR-X卫星的X波段（9.6 GHz - 3.1 cm）传感器获得的高分辨率雷达图像，分析了陆地线性沙丘和巨型雅丹的雷达散射。沙丘的雷达响应中所见的变化是沙丘和沙丘间散射之间的对比的结果，而对于mega-yardang，这些变化是山脊和侵蚀山谷之间的对比的结果。我们测试了一个简单的表面散射模型，参数来自当地地形和表面粗糙度的估计，准确地再现两种地形的雷达信号变化。我们似乎可以区分两种类型的沙丘--埃及的裸露沙丘和纳米比亚的沙覆盖沙丘，也可以区分两种类型的巨型雅丹--年轻的雅丹。
英文摘要：
The Ku-band (13.8 GHz - 2.2 cm) RADAR instrument onboard the Cassini-Huygens spacecraft has revealed the richness of the surface of Titan, as numerous seas, lakes, rivers, cryo-volcanic flows and vast dune fields have been discovered. Linear dunes are a major geomorphological feature present on Titan, covering up to 17% of its surface, mainly in equatorial regions. However, the resolution of the RADAR instrument is not good enough to allow a detailed study of the morphology of these features. In addition, other linear wind-related landforms, such as mega-yardangs (linear wind-abraded ridges formed in cohesive rocks), are likely to present a comparable radar signature that could be confused with the one of dunes. We conducted a comparative study of the radar radiometry of both linear dunes and mega-yardangs, based on representative terrestrial analogues: the linear dunes located in the Great Sand Sea in western Egypt and in the Namib Desert in Namibia, and the mega-yardangs observed in the Lut Desert in eastern Iran and in the Borkou Desert in northern Chad. We analysed the radar scattering of both terrestrial linear dunes and mega-yardangs, using high-resolution radar images acquired by the X-band (9.6 GHz - 3.1 cm) sensor of the TerraSAR-X satellite. Variations seen in the radar response of dunes are the result of a contrast between the dune and interdune scattering, while for mega-yardangs these variations are the result of a contrast between ridges and erosion valleys. We tested a simple surface scattering model, with parameters derived from the local topography and surface roughness estimates, to accurately reproduce the radar signal variations for both landforms. It appears that we can discriminate between two types of dunes - bare interdunes as in Egypt and sand-covered interdunes as in Namibia, and between two types of mega-yardangs - young yardangs...
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