Global exploration of the upper atmosphere of Mars using radio occultation measurements

长期以来，火星上层大气层的结构一直鲜为人知，只有零星的测量数据，直到最近，美国国家航空航天局的MAVEN和欧空局的火星快车和外部火星航天器访问了这颗行星，并携带相关仪器探索大气层100公里以上的区域。这颗行星的电离层是使用无线电掩星技术探测的，即当航天器消失在行星后面时，深空网络跟踪和测量从航天器发出的无线电信号。这项技术允许推断电子密度的垂直分布，但由于几何学的性质，只能对黎明和黄昏区域进行采样，而不能对白边和黑夜区域进行采样，这对我们理解化学和传输过程(风)至关重要。为了克服这一限制，欧洲航天局最近首次在火星航天器到航天器之间的掩星观测中进行了试验，对任何区域、白天和夜晚进行了采样。博士项目将包括探索这个新的数据集，它将提供给我们并由博士生进行分析。他将从他之前在欧空局期间开发的一项技术开始，并在此基础上发展，以获得一种强大而可靠的技术来减少过去和未来的数据集。因此，除了开发出一种可用于未来行星探索的方法外，该学生还将获得电离层电子密度的数据集，该数据集可以进一步研究结构异常，包括火星地壳磁场对电离层结构的影响，并通过使用和进一步开发该小组提供的化学和传输模型，有助于确定塑造火星电离层的主要过程。

The structure of the upper atmosphere of Mars has long remained poorly known, with only sporadic measurements available until recently, when Nasa's MAVEN and ESA's Mars Express and ExoMars spacecraft visited the planet with the relevant instrumentation to explore regions above 100 km in the atmosphere. The planet's ionosphere was explored using the technique of radio occultations, whereby a radio signal emitted from the spacecraft is traced and measured by the Deep Space Network as the spacecraft disappears behind the planet. This techniques allows vertical profiles of electron densities to be inferred, but by nature of the geometry only the dawn and dusk regions can be sampled, not the dayside and nightside regions which are known to be crucial for our understanding of chemistry and transport processes (winds). To overcome this limitation, ESA recently trialled for the first time ever at Mars spacecraft-to-spacecraft occultations, sampling any region, the dayside and the nightside. The PhD project will consist in exploring this new dataset which will be made available to us and analysed by the PhD student. He will start with a technique he previously developed during his time at ESA and build on that in order to obtain a robust and reliable technique for reducing past and future datasets. Thereby, the student, in addition to having developed a methodology which can be used in future planetary explorations, will obtain a dataset of ionospheric electron densities which can be further investigated for structural anomalies, including the effects of Mars' crustal magnetic fields on ionospheric structures and, by using and further developing chemistry and transport models available in the group, contribute towards identifying the main processes shaping the ionosphere of Mars.