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

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 telescopes
2. 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 stars
2. 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.

The focus of the fellowship has significant potential for industrial impact as well as high quality academic outputs. This is described in more detail in the 'pathways to impact' plan but briefly discussed below.

1. Free-space optical communications
Free-space optical communication enables increased data rates and security of transmissions compared to traditional radio communication. I have identified and discussed potential collaborations with several industrial partners in the UK, including Surrey Satellite Technologies Ltd. (SSTL) and Defence Science and Technology Laboratory (DSTL). Applications include as terrestrial telecoms and Earth observation science.

SSTL is the world leading small satellite supplier. In order to remain a leader in this very competitive field, SSTL need to increase the resolution of images of the Earth by increasing the data transmission rates between the satellites and the ground. I will use the information from my 24-hour turbulence monitor and turbulence forecasting to work with SSTL to develop optical communication capabilities. This is an ambitious goal with a significant change to their communication terminals. I expect this to develop over the next ten years.

2. Aviation industry
Damage, delays and disruption due to atmospheric turbulence is estimated to cost the aviation industry hundreds of millions of pounds and approximately 40 fatalities a year (NCAR RAL). Accurate measurement and forecasting can reduce this by helping pilots avoid turbulent zones. I will work with Prof. Williams at the University of Reading to exploit my work in this economically and ecologically important field and bring it into the aviation industry in the UK and abroad. Given the significant drive to reduce the environmental impact of the aviation industry I expect this work to influence the actions of the aviation industry within the time frame of this fellowship (7 years).

3. Astronomy
For astronomy, many large observatories are already moving towards service mode, where the observatory undertakes the observations rather than the astronomer. Without the astronomer needing to travel to the observatory, my global turbulence forecast could be implemented into a flexible scheduling routine to maximise the scientific output of all observatories by ensuring that the most sensitive measurements to be scheduled at the optimal time. I expect observatories to adopt this process within the time frame of this fellowship.

4. Climate Change
Atmospheric turbulence is caused by the mixing of air of different temperatures. This is becoming more intense and more frequent as our climate changes. Therefore, the statistical turbulence trends from the re-processing of archived weather forecasts with my global turbulence forecast algorithms will inform climate change scientists with objective measurements of the rate at which the Earth's atmosphere is becoming more turbulent (or not).

Dissemination
Where applicable I will make the software available through routes such as GitHub. My turbulence forecasts models will be hosted on a website and will be freely available. Concepts, progress and results will be widely disseminated at international conferences, workshops and in peer-reviewed journals.

Public Engagement
Extra-solar planets are a topic of great interest to the general public and local astronomy groups. Within this project I will engage with the public through school visits and more technical workshops with local astronomy groups.
I will look to promote my research at public outreach events such as the Durham Science Festival and explore the potential to exhibit at the Royal Society summer exhibitions where Durham has an outstanding track record of successful applications. I am also perusing dissemination through the media and have had a piece accepted into the 'The Conversation', in order to explain the context of my work to the widest possible audience.