Mapping SO2 frost on Io by the modeling of NIMS hyperspectral images
Mapping SO2 frost on Io by the modeling of NIMS hyperspectral images
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DOI：
10.1006/icar.2000.6513
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发表时间：
2001-01-01
期刊：
影响因子：
3.2
通讯作者：
Shirley, J
中科院分区：
文献类型：
--
作者：
Douté, S;Schmitt, B;Shirley, J
我们分析了伽利略的近红外测绘光谱仪(NIMS)在木星G2至E16轨道期间获取的木卫一高光谱图像。这一分析导致了约四分之三的木卫一表面上的二氧化硫霜冻沉积的地理分布和物理特征。这些矿床是各种现象的极好示踪者，包括火山产生和排放、大气输送、冷凝、变质、辐射和升华，这些现象发生在整个SO2循环中。我们认为，固体SO2的沉积物光学厚度很大，在地理上与其他含硫化合物混合。我们首先利用两个不同位置的光谱序列在很大的相角范围内评估了SO2霜层的平均中等后向散射行为(Henyey Greenstein相函数参数g=-0.27+/-0.05)。这一行为可能表明有许多缺陷的颗粒状纹理或蓬松的纹理。其次，基于可变粒度纯SO2与光谱中性单元混合的线性光谱模型，实现了对高光谱图像的更系统的反演。因此，我们制作了两个全球马赛克，它们映射了SO2霜冻覆盖率和平均颗粒大小。在本研究的空间尺度上(约200公里)，SO2沉积物在IOO表面无处不在，但SO2霜冻集中在以中纬度为中心的几个大范围内。这些SO2富集区(地表覆盖率大于60%)与纬度较低的羽流具有纵向相关性，表明这些羽流是SO2气体的主要来源。在羽状物周围或赤道可能发生动态凝结后，气体被太阳或热通量重新动员，并主要在纬向上流向最冷和最近的没有热点的地区。第三，分布和粒度镶嵌的相关性区分了四个不同的SO2物理单元，它们反映了凝聚、变质和升华的相对区域差异。最后，与旅行者紫外线(A.S，McEwen，T.V.Johnson，D，L.Matson，and L.A.Soderblom，1988，Icarus，Vol.75，pp.450-478)和伽利略可见光(P.Geissler，A.S，McEwen，L.Keszthelyi，R.M.Lope-Gautier，J.Granahan，and D.P.Simonelli，1999，Icarus，Vol.140，pp.256-282)的观察结果相比较，证明了在中高纬度地区二氧化硫的分子污染，这些被污染的二氧化硫沉积物可能是光学上很薄的。(C)2000年学术出版社。
We analyze a collection of hyperspectral images of Io acquired by the near infrared mapping spectrometer (NIMS) of Galileo during the G2 to E16 orbits of Jupiter. This analysis leads to the geographical distribution and physical characterization of SO2 frost deposits over about three-fourths of Io's surface. These deposits are excellent tracers of various phenomena, including volcanic production and emission, atmospheric transportation, condensation, metamorphism, irradiation, and sublimation, that occur throughout the SO2 cycle, We assume that the deposits of solid SO2 are optically thick and are geographically mixed with other sulfur-bearing compounds. We first assess the mean moderate backscattering behavior of the SO2 frost (Henyey Greenstein phase function parameter g = -0.27 +/- 0.05) using a sequence of spectra at two different locations over a large range of phase angles. This behavior may indicate a granular texture with many defects or a fluffy texture. Second, a more systematic inversion of the hyperspectral images is achieved based on a linear spectral model of pure SO2 with variable grain size mixed with a spectrally neutral unit. As a result, we produce two global mosaics that map SO2 frost coverage and mean grain size. SO2 deposits are omnipresent on Io's surface at the spatial scale of this study (approximate to 200 km), but the SO2 frost is concentrated within several large areas centered at medium latitudes. These SO2-rich regions (surface coverage higher than 60%) show a longitudinal correlation with plumes located lower in latitude, suggesting that these plumes are the principal sources of SO2 gas. After a possible dynamic condensation around the plumes or at the equator, the gas is remobilized by the solar or thermal fluxes and flows mostly latitudinally toward the coldest and nearest regions devoid of hot-spots. Third, the correlation of the distribution and grain size mosaics distinguishes four different SO2 physical units that indicate relative regional variations of condensation, metamorphism, and sublimation. Finally, comparisons with Voyager ultraviolet (A. S, McEwen, T. V. Johnson, D, L. Matson, and L. A. Soderblom, 1988, Icarus, Vol. 75, pp. 450-478) and Galileo visible (P. Geissler, A. S, McEwen, L. Keszthelyi, R. M. C. Lopes-Gautier, J. Granahan, and D. P. Simonelli, 1999, Icarus, Vol. 140, pp. 256-282) observations demonstrate molecular contamination of SO2 at medium and high latitudes and that these contaminated SO2 deposits may be optically thin. (C) 2000 Academic Press.