Stopping the stars from twinkling: Unlocking the potential of ground-based telescopes for astronomy and free-space optical communication

目的：建立本地和全球大气湍流的强大3D模型，以便i)常规地描述小型过境系外行星的大气特征；ii)通过支持从传统无线电波到更快、更便宜和更安全的自由空间光通信（FSOC）的过渡来改善卫星通信。地面天文学和FSOC目前都受到地球湍流大气的限制。通过开拓大气特征和校正的新概念，我将：使地面望远镜的天文观测能够与太空望远镜相媲美，甚至有可能优于太空望远镜。在地面和轨道卫星之间实现定期，稳健和持续的FSOC连接。这些创新技术有多种应用，包括：了解围绕遥远恒星运行的类地小型系外行星。检索用于地球观测、行星际和深空任务的空间科学卫星的数据。研究系外行星有很多理由。这些任务的范围从试图了解太阳系的形成和演化，到寻找地外生命。前者将使我们能够探索存在的世界的巨大多样性，并在一个全新的层面上发现物理宇宙。后者非常令人兴奋，对整个人类都有影响。仅仅探测到一颗系外行星是不够的，我们还必须描述这些行星的特征，以确定它们是什么样的。有几种方法来描述系外行星。其中最强大，当然也是最有效的方法之一是过境法。当行星从恒星前面经过时，它会挡住一些光线。这种强度的减弱可以通过望远镜观察到，并被用来推断出是否存在一颗绕着遥远恒星运行的系外行星，以及关于它的大量信息。这颗行星在几个波长上吸收或发射的光的数量，让我们对这颗系外行星大气的温度分布、动力学、组成和天气系统有了详细的了解。几次大型凌日观测，如TESS和NGTS， HARPS和HARPS- n的径向速度观测，以及未来的太空卫星，如CHEOPS和PLATO，将提供大量有趣的目标，需要精确的跟踪。通过使用大的收集区域和多个地面望远镜的可访问性，可以获得额外的精度，这将允许对遥远的小型系外行星的大气进行常规和有针对性的表征。然而，这超出了当前的能力。地球的大气层引起强度波动，称为闪烁，肉眼可以看到闪烁。这种闪烁限制了地面观测比地球大许多倍的系外行星的灵敏度。除了天文学之外，最近不断扩大的FSOC领域也存在着非常相似的问题。与传统的无线电通信相比，使用光学波长的大带宽将使用于地球观测、行星际和深空任务的空间科学卫星能够检索到10-100倍的数据。传输速率的增加类似于从传统的铜缆转向光纤。此外，通过转换到光波长，我们可以满足世界各地社会已经习惯的更高容量数据传输的需求。通过结合使用新型仪器表征地球大气湍流，以及我正在开发的全球湍流数值预测模型，我将评估地球大气对天文学和FSOC的影响，并开发新的校正机制，包括层析闪烁校正。只有结合这些主题，我们才能真正释放地面望远镜的全部潜力。

Aim: To build robust 3D models of both local and global atmospheric turbulence, in order to i) routinely characterise the atmospheres of small transiting exoplanets and ii) improve satellite communication by supporting the transition from traditional radio waves to faster, cheaper and more secure Free Space Optical Communication (FSOC).Ground-based astronomy and FSOC are both currently limited by the Earth's turbulent atmosphere. By pioneering new concepts in atmospheric characterisation and correction, I will: 1. enable astronomical observations from ground-based telescopes to be comparable to, and potentially better than, space telescopes2. enable regular, robust and sustained FSOC links between the ground and orbiting satellites.These innovative techniques have multiple applications, including:1. learning about small Earth-like exoplanets orbiting distant stars2. retrieving data from space science satellites used for Earth observation, inter-planetary and deep space missions. There are many reasons to study exoplanets. These range from trying to understand how solar systems form and evolve, to the search for extra-terrestrial life. The former will allow us to explore the vast diversity of worlds that exist and to discover the physical universe on a whole new level. The latter being incredibly exciting with implications for the whole of humanity.Simply detecting an exoplanet is not enough, we must also characterise these planets in order to ascertain what they are like. There are several ways to characterise exoplanets. One of the most powerful and certainly the most productive is the transit method. As a planet passes in front of a star it blocks some of the light. This reduction in intensity is observable by telescopes and is used to deduce the presence of an exoplanet orbiting a distant star and a wealth of information about it. The amount of light absorbed or emitted by the planet in several wavelengths gives us a detailed impression of the temperature distribution, dynamics, composition and weather systems of the exoplanet's atmosphere.Several large transits surveys such as TESS and NGTS and the radial-velocity surveys of HARPS and HARPS-N, together with future space satellites such as CHEOPS and PLATO, will provide abundant interesting targets which will require precise follow-up. The extra precision attainable by using the large collecting areas and the accessibility of multiple ground-based telescopes would allow the routine and targeted characterisation of the atmospheres of distant small exoplanets. However, this is beyond current capabilities.The Earth's atmosphere causes intensity fluctuations, called scintillation, which can be seen as twinkling by the naked eye. This twinkling limits the sensitivity of ground-based observations to that of exoplanets many times larger than the Earth.In addition to astronomy, the recently expanding field of FSOC has very similar problems. The large bandwidth of using optical wavelengths, as opposed to conventional radio communication, will enable 10-100 times more data to be retrieved from space science satellites used for Earth observation, inter-planetary and deep space missions. This increase in transmission rates is analogous to moving from traditional copper cables to fibre optics. In addition, by transitioning to optical wavelengths, we can meet demands for higher capacity data transmissions that societies around the world have become accustomed to. Through a combination of characterising the Earth's atmospheric turbulence using novel instrumentation, with a numerical global turbulence forecast model, which I am developing, I will assess the implications of the Earth's atmosphere on astronomy and FSOC and develop new correction mechanisms, including tomographic scintillation correction. It is only with the combination of these themes can we truly unlock the full potential of ground-based telescopes.