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首页> 外文期刊>Planetary and space science >Correlations between Cassini VIMS spectra and RADAR SAR images: Implications for Titan's surface composition and the character of the Huygens Probe Landing Site
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Correlations between Cassini VIMS spectra and RADAR SAR images: Implications for Titan's surface composition and the character of the Huygens Probe Landing Site

机译：卡西尼号VIMS光谱与RADAR SAR图像之间的相关性：对土卫六表面成分和惠更斯探测器着陆点特征的暗示

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摘要

Titan's vast equatorial fields of RADAR-dark longitudinal dunes seen in Cassini RADAR synthetic aperture images correlate with one of two dark surface units discriminated as "brown" and "blue" in Visible and Infrared Mapping Spectrometer (VIMS) color composites of short-wavelength infrared spectral cubes (RGB as 2.0, 1.6, 1.3 μm). In such composites bluer materials exhibit higher reflectance at 1.3 μm and lower at 1.6 and 2.0 μm. The dark brown unit is highly correlated with the RADAR-dark dunes. The dark brown unit shows less evidence of water ice suggesting that the saltating grains of the dunes are largely composed of hydrocarbons and/or nitriles. In general, the bright units also show less evidence of absorption due to water ice and are inferred to consist of deposits of bright fine precipitating tholin aerosol dust. Some set of chemical/mechanical processes may be converting the bright fine-grained aerosol deposits into the dark saltating hydrocarbon and/or nitrile grains. Alternatively the dark dune materials may be derived from a different type of air aerosol photochemical product than are the bright materials. In our model, both the bright aerosol and dark hydrocarbon dune deposits mantle the VIMS dark blue water ice-rich substrate. We postulate that the bright mantles are effectively invisible (transparent) in RADAR synthetic aperture radar (SAR) images leading to lack of correlation in the RADAR images with optically bright mantling units. RADAR images mostly show only dark dunes and the water ice substrate that varies in roughness, fracturing, and porosity. If the rate of deposition of bright aerosol is 0.001-0.01 μm/yr, the surface would be coated (to optical instruments) in hundreds-to-thousands of years unless cleansing processes are active. The dark dunes must be mobile on this very short timescale to prevent the accumulation of bright coatings. Huygens landed in a region of the VIMS bright and dark blue materials and about 30 km south of the nearest occurrence of dunes visible in the RADAR SAR images. Fluvial/pluvial processes, every few centuries or millennia, must be cleansing the dark floors of the incised channels and scouring the dark plains at the Huygens landing site both imaged by Descent Imager/Spectral Radiometer (DISR).
机译：在卡西尼（Cassini）雷达合成孔径图像中看到的泰坦（Titan）宽广的RADAR暗纵向沙丘场与短波红外可见光和红外映射光谱仪（VIMS）彩色复合材料中被区分为“棕色”和“蓝色”的两个黑暗表面单位之一相关光谱立方体（RGB为2.0、1.6、1.3μm）。在此类复合材料中，较蓝的材料在1.3μm处显示较高的反射率，而在1.6和2.0μm处显示较低的反射率。深棕色单位与RADAR深沙丘高度相关。深棕色单位显示出很少的水冰迹象，表明沙丘的盐粒主要由碳氢化合物和/或腈组成。通常，明亮的单位还显示出因水冰而被吸收的证据较少，并且推断为明亮的细小沉淀的索林气溶胶粉尘沉积物组成。某些化学/机械过程可能会将明亮的细颗粒气溶胶沉积物转化为深色的盐化碳氢化合物和/或腈颗粒。或者，暗沙丘材料可衍生自与亮材料不同类型的空气气溶胶光化学产品。在我们的模型中，明亮的气溶胶和深色碳氢化合物沙丘都会沉积VIMS深蓝色水富含冰的基​​质。我们假设亮地幔在RADAR合成孔径雷达（SAR）图像中实际上是不可见的（透明），从而导致具有光学亮地幔单元的RADAR图像缺乏相关性。 RADAR图像大多数仅显示暗沙丘和水冰基质，其粗糙度，裂缝和孔隙度均发生变化。如果明亮的气溶胶的沉积速率为0.001-0.01μm/ yr，则除非进行清洁过程，否则表面将在数十万年内被涂覆（使用光学仪器）。深色沙丘必须在很短的时间内移动，以防止堆积明亮的涂层。惠更斯降落在VIMS明亮和深蓝色物质的区域内，在雷达SAR图像中可见的最近沙丘以南约30公里处。每隔几个世纪或几千年的冲积/冲积过程必须清理下降的通道的深色地面，并在惠更斯着陆点的深色平原上进行冲刷，两者均由下降成像仪/光谱辐射仪（DISR）进行成像。

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