Looking through the Turbulent Sky

Images captured by ground-based telescopes are blurred due to the turbulence of the atmosphere. We have been working on algorithms for deformable mirrors which have to be adjusted 3000 times a second for sharp images.

Problem overview

Turbulence in the atmosphere leads to different densities of air and therefore to different speeds of light, which makes uncorrected images of ground-based telescopes blurred.
Uncorrected image of the star HIC 59206.
After switching on the Adaptive Optics System of VLT, it is visible that it is a double star. Credit: ESO.
The Very Large Teslecope (VLT) of the European Southern Observatory (ESO) has a diameter of the primary mirror of 8.2m. With the planned European Extremely Large Telescope (E-ELT, 39m primary mirror), the separability of two objects becomes much narrower, and the computational requirements on Adaptive Optics Systems are much more demanding. To be more specific, for certain applications 60.000 actuators of deformable mirrors have to be adjusted 3000 times per second.
This illustration shows how adaptive optics work.

Results and achievements

Austria joined ESO in 2008. As a part of Austria’s contribution to ESO, a team doing research and algorithm development on Adaptive optics was formed, consisting of the Industrial Mathematics Institute (Kepler University), the Radon Institute for Computational and Applied Mathematics of the Austrian Academy of Sciences, and of MathConsult.

From 2009 to 2013, a variety of algorithms for different Adaptive Optics Settings was developed: our Cumulative Reconstructor (CuRe) was improved by domain decomposition (CuReD) and parallelization.

Typical speed-ups over the until then widely used matrix vector multiplication (MVM) were between 20 and 1100. This makes adaptive optics systems also feasible for the E-ELT, where response times of 100 microseconds should be achieved.

Artist’s impression of the European Extremely Large Telescope (E-ELT) in its enclosure on Cerro Armazones, a 3060-metre mountaintop in Chile’s Atacama Desert. The 39-metre E-ELT will be the largest optical/infrared telescope in the world — the world’s biggest eye on the sky. Operations are planned to start early in the next decade, and the E-ELT will tackle some of the biggest scientific challenges of our time. The design for the E-ELT shown here is preliminary.

Further Reading:

Matthias Rosensteiner: Advanced algorithms for astronomical adaptive optics, Ph.D. thesis, Johannes Kepler University, 2013.