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The VIRTIS-M instrument on Venus Express is a mapping infrared spectrometer intended for the study of the atmosphere of Venus. As there are several atmospheric windows in the near-infrared through which radiation from the surface leaks into space, it is possible to use data from VIRTIS-M to investigate the surface of Venus. Previous ground-based investigations e.g. by Meadows and Crisp (1996) found no significant variations in the surface infrared emissivity. Hashimoto and Sugita (2003) showed that these previous studies omitted to account for multiple surface-cloud reflections and that by doing so a much higher emissivity contrast might be expected. They further considered the possibility to distinguish between granitic and basaltic rock when given a sufficient accuracy of infrared emissivity measurements. Basaltic volcanic flood plain is the most common type of surface on Venus but the composition of the highly deformed highlands is still unknown. Campbell and Taylor (1983) speculated that these highlands might contain granitic rock and thus 'resemble terrestrial Archean continental nuclei'. Confirmation of this supposed composition would strengthen the interpretation of the high D/H ratio in the atmosphere as a remnant of an ocean because liquid surface water is required for the formation of granites. For my diploma thesis I am implementing the method from Hashimoto and Sugita (2003) to calculate maps of surface emissivity from VIRTIS-M data. After the arrival of Venus Express at Venus in April we will test and enhance my algorithm using the VIRTIS-M data. By the time of October we should be able to present some first results on the retrieval of emissivities and a preliminary discussion of the implication for the surface composition. The VIRTIS-M data will greatly improve the existing data on Venus surface infrared emissivity as previous studies were either earth-based or, in case of Galileo-NIMS, of limited spectral resolution. The data might put important constraints on our knowledge of the atmospherical and geological evolution on Venus and in general on the habitability of planets. Literature: Meadows and Crisp (1996): Ground based near-infrared observations of the Venus nightside: The thermal structure and water abundance near the surface, J. Geophys. Res., 97, 15,967-15,976 Hashimoto and Sugita (2003): On observing the compositional variability of the surface of Venus using nightside near-infrared thermal radiation, J. Geophys. Res., 108(E9), 5109 Campbell and Taylor(1983): No water no granites - No oceans, no continents, Geophys. Res. Lett., 10, 1061-1064
机译:Venus Express上的VIRTIS-M仪器是一种映射红外光谱仪,旨在研究维纳斯的大气。由于近红外中有几个大气窗口,来自表面的辐射会通过这些窗口泄漏到太空中,因此有可能使用VIRTIS-M的数据来调查金星的表面。以前的地面调查,例如Meadows和Crisp(1996)的研究发现表面红外发射率没有明显变化。 Hashimoto和Sugita(2003)指出,这些先前的研究由于考虑了多次表面云反射而被省略,通过这样做,可以期望得到更高的发射率对比。他们还考虑了在给出足够高的红外发射率测量精度的情况下区分花岗岩和玄武岩的可能性。玄武岩火山泛滥平原是金星上最常见的地表类型,但高度变形的高地的组成仍然未知。坎贝尔和泰勒(Campbell and Taylor,1983)推测这些高地可能含有花岗质岩石,因此“类似于陆生太古宙大陆核”。对这种假定成分的确认将加强对大气中高D / H比作为海洋残余物的解释,因为花岗岩的形成需要液态地表水。对于我的毕业论文,我正在实施Hashimoto和Sugita(2003)的方法,以根据VIRTIS-M数据计算表面发射率图。在4月Venus Express到达Venus之后,我们将使用VIRTIS-M数据测试和增强我的算法。到十月时,我们应该能够提出一些有关发射率检索的初步结果,并初步讨论表面成分的含义。 VIRTIS-M数据将极大地改善金星表面红外发射率的现有数据,因为先前的研究要么是基于地球的研究,要么是Galileo-NIMS,其光谱分辨率有限。这些数据可能对我们对金星的大气和地质演化的知识以及总体上对行星的可居住性施加了重要的限制。文献:Meadows and Crisp(1996):金星夜边的地面近红外观测:地表附近的热结构和水丰度,J。Geophys。 Res。,97,15,967-15,976 Hashimoto和Sugita(2003):关于使用夜间近红外热辐射观察金星表面的成分变化,J。Geophys。 Res。,108(E9),5109 Campbell and Taylor(1983):无水无花岗岩-无海洋,无大洲,地球物理学。 Res。 Lett。,10,1061-1064



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