It is conventional for satellites and Earth-based stations to communicate using radio transmissions. At these wavelengths the atmosphere is transparent. However, a revolutionary technology is emerging that harnesses the capability of performing these transmissions at optical wavelengths. A compelling advantage of free-space optical communication is that it would increase the current rate of data transfer by many orders of magnitude. It is believed that this will lead the way towards future generations having worldwide high-speed internet access. Another driving force is that the realisation of this technology would transform deep space exploration.

Optical wavefronts from a celestial source propagate freely through outer space. It is only in the last fraction of their journey towards the Earth – where they propagate through atmospheric turbulence – that they become perturbed. The source of this image blurring is the constant mixing of different temperatures throughout the atmosphere, causing the wavefront to travel through regions of varying refractive index. These aberrations are so severe that they prevent optical ground-space links from being established.

One of the most promising solutions for mitigating the effects of atmospheric turbulence is Adaptive Optics (AO) – a real-time technology that corrects for wavefront aberrations by first measuring their integrated strength. The wind drives atmospheric turbulence. Therefore, these AO systems must be updated thousands of times per second. The entire performance of the AO system depends on the strength and speed distribution of turbulent layers throughout the atmosphere. Characterising these atmospheric parameters is critical for optimised AO performance, AO performance verification and automated site ranking, i.e. spacecraft can use this information to select the ground station currently best suited for stable communication.

The project will focus on optimising AO system performance for free-space optical communication. Its research topics will cover techniques for characterising the effects of atmospheric turbulence. DLR has already developed a number of sophisticated instruments that have taken data at world-leading observatories. The student will be tasked with further developing existing software tools for analysing this data. They will have access to advanced simulation software and high-performance computing hardware. It is hoped that they will support scientific measurement campaigns, and use this opportunity to test their developed concepts on-sky. Novel ideas will be encouraged.

Activities:

• theoretical analysis of optical wavefront propagation
• implementation and performance analysis of novel algorithms
• evaluation of measurements and analysis of the results
• writing and maintaining advanced software packages
• concise presentation of results and further ideas
• possible participation in on-sky measurement campaigns