title: Building resilient optical ground station networks with atmospheric characterisation and modelling
Creators: name: Birch, Marcus
Publisher: name: The Australian National University
Year: 2024

description: Optical communication over free-space is heralded to be a revolution for satellite telecommunication that will amplify the data capability of satellites, support future space exploration, and bring the world closer through high-speed relays. Laser links capable of modulation up to Tbit/s are promising but despite such promise this technology has long struggled with adoption for space-to-ground links due to the challenges of Earth's atmosphere. Atmospheric attenuation from cloud and turbulence are the core impediments of the atmospheric channel. Cloud cover presents an impenetrable barrier in nearly all cases for space-to-ground links, and so well-placed sites along with proliferation have long been accepted as the only solution. Atmospheric turbulence can create phase and intensity noise that limits the data rate of optical links, and is far more complex than cloud to characterise and model. Overcoming both of these problems requires new solutions on where to place optical ground stations (OGS), and new ways to measure atmospheric turbulence at those sites. I therefore addresses two core questions which arise from overcoming the atmosphere, i.e. how should ground networks be designed for resilience against cloud-induced outages, and how atmospheric turbulence can be characterised. I present novel methodology for analysing the capability of OGS networks with a focus on Australia, leveraging remote-sensing data and orbital simulations to show not only how the region is well-suited to optical communication, but utility of these analysis tools. Among these methods is a semi-analytical solution to reliability for spatially-correlated nodes, and a spatially-resolved means of node placement optimisation. These methods are extended to the poles, where further simulations and meteorological instruments installed at Davis Station, Antarctica, are used to provide a compelling case for the poles to host an OGS. This includes leveraging a machine-learning approach to cloud phase classification in-situ to refine outage predictions in polar climates. The network frameworks presented here synergise with the development of a novel turbulence monitor that can be easily deployed at prospective sites. An automated Ring Image Next Generation Scintillation Sensor (RINGSS) is constructed and tested at a number of locations, including a proof-of-concept campaign at urban sites in Europe and the Arctic. An infrared RINGSS variant is also built and deployed at the NASA/Jet Propulsion Laboratory OGS, where I demonstrate the first profiling of atmospheric turbulence using a spacecraft laser terminal, and the first use of RINGSS in daytime. Presented results in OGS network analysis and atmospheric site-testing are grounded in the ongoing development of an Australasian network, and a ANU OGS node that has been constructed over the past three years at Mount Stromlo Observatory. My research therefore establishes a comprehensive toolkit to help design and deploy free-space optical communication networks, and significantly improve their resilience and efficiency. Reliable optical ground station networks will form the backbone of a future satellite communication landscape which will amplify all of humanities future endeavours in space and on Earth in much the same way that radio antenna revolutionised telecommunication.