从ExoMars微量气体轨道飞行器上的TIRVIM/ACS得到的火星大气中的热结构和气溶胶：检索算法的确认
Thermal structure and aerosols in Mars' atmosphere from TIRVIM/ACS onboard the ExoMars Trace Gas Orbiter : validation of the retrieval algorithm
摘要：
ExoMars微量气体轨道器（TGO）上的大气化学套件（ACS）通过红外线的不同光谱间隔监测火星大气。我们提出了一个检索算法，专门用于分析TIRVIM（ACS的热红外通道）在最低点几何条件下获得的光谱。我们的算法同时反演大气温度垂直廓线高达50公里，地面温度，和综合光学厚度的尘埃和水冰云。TIRVIM数据集的特异性在于它能够在54个太阳日的时间内解析日周期。然而，在一天中的不同时间，所需的大气量能准确估计到什么程度还不确定。在这里，我们首先提出了一个观测系统模拟实验（OSSE）。我们在不同的纬度，季节和当地时间产生合成观测，并在这些合成数据上运行我们的检索算法，以评估其鲁棒性。不同来源的偏见的文件，特别是关于气溶胶检索。大气温度反演被发现强大的，即使灰尘和/或水冰云不透明度没有很好地估计在我们的OSSE。然后，我们将我们的算法应用于2018年4月至5月的TIRVIM观测，并通过与数千个位于同一地点的火星气候探测器（MCS）检索进行比较，对检索的大气温度和尘埃综合不透明度进行交叉验证。TIRVIM和MCS大气温度之间的大部分差异可以归因于垂直敏感性的差异。白天的尘埃不透明度彼此一致，而在这个季节的TIRVIM夜间尘埃不透明度被发现的偏差。
英文摘要：
The Atmospheric Chemistry Suite (ACS) onboard the ExoMars Trace Gas Orbiter (TGO) monitors the Martian atmosphere through different spectral intervals in the infrared light. We present a retrieval algorithm tailored to the analysis of spectra acquired in nadir geometry by TIRVIM, the thermal infrared channel of ACS. Our algorithm simultaneously retrieves vertical profile of atmospheric temperature up to 50 km, surface temperature, and integrated optical depth of dust and water ice clouds. The specificity of the TIRVIM dataset lies in its capacity to resolve the diurnal cycle over a 54 sol period. However, it is uncertain to what extent can the desired atmospheric quantities be accurately estimated at different times of day. Here we first present an Observing System Simulation Experiment (OSSE). We produce synthetic observations at various latitudes, seasons and local times and run our retrieval algorithm on these synthetic data, to evaluate its robustness. Different sources of biases are documented, in particular regarding aerosol retrievals. Atmospheric temperature retrievals are found robust even when dust and/or water ice cloud opacities are not well estimated in our OSSE. We then apply our algorithm to TIRVIM observations in April-May, 2018 and perform a cross-validation of retrieved atmospheric temperature and dust integrated opacity by comparisons with thousands of co-located Mars Climate Sounder (MCS) retrievals. Most differences between TIRVIM and MCS atmospheric temperatures can be attributed to differences in vertical sensitivity. Daytime dust opacities agree well with each other, while biases are found in nighttime dust opacity retrieved from TIRVIM at this season.
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