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题名: 火星CH_4气体空间密度分布的反演
其他题名: Reconstruction of martian methanes spatial density distribution
作者: 黄娅; 程炳钧; 刘学旺; 沈超; 张艺腾; 李磊; 张灵倩
作者部门: 空间科学部
关键词: 火星 ; 反演
刊名: 科学通报
ISSN号: 0023-074X
出版日期: 2016
卷号: 61, 期号:16, 页码:1822-1827
收录类别: CSCD
项目资助者: 空间天气学国家重点实验室(专项和开放)基金 ; 国家自然科学基金
中文摘要: 目前对火星CH_4气体的探测是探索火星生命的一项重要手段, 圈定出火星表面CH_4源区的位置可为将来火星生命的探索选取合适的目标点. 本文在对火星CH_4气体共振散射进行探测的基础上, 通过数值模拟的方法对火星CH_4气体的空间分布进行了反演. 反演结果能再现模型的密度分布, 辨认出CH_4气体密度分布较为稠密的区域, 从而可以确定出火星表面CH_4源区的位置.
英文摘要: The exploration of martian methane (CH_4) is the important way to search life on the Mars. The determination of the source region of CH_4 provides an appropriate target location that explorer the possible lives on the Mars. So it requires us to know the spatial density distribution of CH_4, thus the densest source region of CH_4 can be identified. In deep space exploration, there is long history for scientists to detect the characteristic spectrum from resonance scattering of the gas molecular as a result of solar radiation. For example, in 1995, the European Space Agency detected the 3.3 nm fluorescence from CH_4 through Space Telescope. At present, the project team is trying to study the possibility of exploration of the CH_4 resonance scattering on Mars, which is the base for this paper. Since the gas of CH_4 is very thin, and the rescattering can be negligible, so it can be approximated as an optically thin layer, and the measured brightness is proportional to the column abundance of the CH_4 along the lines of imager radiation corresponding to each pixel. This process is very similar with the emission computed tomography (ECT), so the computed tomography (CT) can be used to calculate the CH_4 spatial density distribution when the data could be collected from various angles. In the strict sense, the accurate reconstruction needs the projection data satisfy the Tuy-Smith sufficiency condition. But this condition is very difficult for the satellite. In 2006, Sidky et al developed an algebraic reconstruction technique(ART) based on the minimization of the image total variation (TV) that applies to insufficient data problems. Therefore, this method is adopted to solve our problems. In order to verify our formulas for the CH_4 density, in this paper, a three dimensional (3D) model for the density distribution of the CH_4 is established based on the Mars atmosphere distribution law, which may not consistent with the truth, but it is enough for verify the formulas. Through the numerical simulation, the density distribution is reconstructed and compared with the 3D model. It is shown that the reconstruction results are in agreement with the model. Especially, it can distinguish the densest region of CH_4, hence, to define the source region of the CH_4 on the Mars surface. So the CT method can be used to calculate the density of CH_4 from the image data. But there are still some problems. Firstly, the results have certain deviation which can be improved by increasing the projection data. For example, reduce the time interval of sampling, change the orbit of the satellite. Additionally, the spatial resolution of the results requires to be improved which is controlled by the one of the detector. According to the detector developed by the project team, the best resolution, both vertical and horizontal, is 50 km, which is too low for the reconstruction. How to improve the resolution of the detector is the problem that the project team is trying to solve. Moreover, the assumption of the steady-state condition for CH_4 is supposed in this work. We ignore the CH_4 motion during taking all the pictures by the Imager, but in fact, this assumption is unreasonable and unacceptable. The recent research showed that the density of CH_4 should vary with time because of the motion of the neutral wind. All these difficulties will be further studied in our future work.
语种: 中文
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内容类型: 期刊论文
URI标识: http://ir.nssc.ac.cn/handle/122/5605
Appears in Collections:空间科学部_期刊论文

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