标题： 线性沙丘和巨型雅丹的雷达散射：应用于土卫六（Titan） 显示英文标题

标题： Radar scattering of linear dunes and mega-yardangs: Application to Titan

摘要： 卡西尼-惠更斯号飞船上的Ku波段（13.8 GHz - 2.2 cm）雷达仪器揭示了泰坦表面的丰富性，发现了大量的海洋、湖泊、河流、冰火山流和广阔的沙丘地。线状沙丘是泰坦上主要的地貌特征之一，覆盖了其表面的多达17%，主要分布在赤道地区。然而，雷达仪器的分辨率不足以进行这些特征形态的详细研究。此外，其他与风有关的线状地貌，如巨型雅丹（由粘结岩石形成的线状风蚀脊），很可能呈现出可与沙丘混淆的雷达信号。我们基于地球上的代表性类比进行了线状沙丘和巨型雅丹雷达辐射度的对比研究：位于埃及西部大沙海中的线状沙丘以及纳米比亚纳米布沙漠中的线状沙丘，以及伊朗东部卢特沙漠和乍得北部博尔库沙漠中观察到的巨型雅丹。我们分析了地球上的线状沙丘和巨型雅丹的雷达散射特性，使用了TerraSAR-X卫星X波段（9.6 GHz - 3.1 cm）传感器获取的高分辨率雷达图像。沙丘雷达响应的变化是由于沙丘与沙丘间散射之间的对比，而对于巨型雅丹来说，这种变化则是由于山脊与侵蚀谷之间的对比。我们测试了一个简单的表面散射模型，该模型的参数来自局部地形和表面粗糙度估计，以准确再现这两种地貌的雷达信号变化。结果表明，我们可以区分两种类型的沙丘——裸露的沙丘间地带（如埃及）和被沙覆盖的沙丘间地带（如纳米比亚），以及两种类型的巨型雅丹——年轻的雅丹…… 显示英文摘要

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...