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首页> 外文期刊>Icarus: International Journal of Solar System Studies >A radiative transfer model to treat infrared molecular excitation in cometary atmospheres
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A radiative transfer model to treat infrared molecular excitation in cometary atmospheres

机译：用于处理彗星大气中红外分子激发的辐射传递模型

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The exospheres of small Solar System bodies are now observed with high spatial resolution from space missions. Interpreting infrared spectra of cometary gases obtained with the VIRTIS experiment onboard the Rosetta cometary mission requires detailed modeling of infrared fluorescence emission in optically thick conditions. Efficient computing methods are required since numerous ro-vibrational lines excited by the Sun need to be considered. We propose a new model working in a 3-D environment to compute numerically the local incoming radiation. It uses a new algorithm using pre-defined directions of ray propagation and ray grids to reduce the CPU cost in time with respect to Monte Carlo methods and to treat correctly the sunlight direction. The model is applied to the v(3) bands of CO2 and H2O at 4.3 mu m and 2.7 mu m respectively, and to the CO v(1 -> 0) band at 4.7 mu m. The results are compared to the ones obtained by a 1-D algorithm which uses the Escape Probability (EP) method, and by a 3-D "Coupled Escape Probability" (CEP) model, for different levels of optical thickness. Our results suggest that the total band flux may vary strongly with azimuth for optically thick cases whereas the azimuth average total band flux computed is close to the one obtained with EP. Our model globally predicts less intensity reduction from opacity than the CEP model of Gersch and A'Hearn (Gersch, A.M., A'Hearn, M.F. [2014]. Astrophys. J. 787, 36-56). An application of the model to the observation of CO2, CO and H2O bands in 67/P atmosphere with VIRTIS is presented to predict the evolution of band optical thickness along the mission. (C) 2015 Elsevier Inc. All rights reserved.
机译：现在，太空任务以较高的空间分辨率观察到了小型太阳系天体的外层。解释通过Rosetta彗星飞行任务上的VIRTIS实验获得的彗星气体的红外光谱，需要对光学厚度较厚的红外荧光发射进行详细建模。需要有效的计算方法，因为需要考虑许多由太阳激发的旋转振动线。我们提出了一种在3-D环境中工作的新模型，以数值计算局部入射辐射。它使用一种新的算法，该算法使用预定义的射线传播方向和射线网格，以相对于蒙特卡洛方法在时间上减少CPU成本，并正确处理阳光方向。该模型分别应用于CO2和H2O的v（3）谱带，分别为4.3μm和2.7μm，以及CO v（1-> 0）谱带，分别为4.7μm。对于不同的光学厚度水平，将结果与通过使用逸出概率（EP）方法的1-D算法和通过3-D“耦合逸出概率”（CEP）模型获得的结果进行比较。我们的结果表明，对于光学较厚的情况，总带通量可能会随方位角而变化很大，而计算出的方位角平均总带通量却接近于使用EP获得的通量。与Gersch和A'Hearn的CEP模型相比，我们的模型在全球范围内预测的不透明强度降低幅度较小（Gersch，A.M.，A'Hearn，M.F. [2014]。Astrophys。J. 787，36-56）。提出了该模型在VIRTIS观测67 / P大气中CO2，CO和H2O波段的应用，以预测沿着任务的波段光学厚度的变化。 （C）2015 Elsevier Inc.保留所有权利。

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