Atmospheric Tomography at Keck Telescope

by Stefan Raffetseder

Using measurements of multiple guide stars in different directions in
an Adaptive Optics system leads to the problem of atmospheric tomogra-
phy. Usually, this problem is solved by an inverse matrix operation, which
requires O (n2) operations. Since the new generation of ground-based tele-
scopes have a diameter of 30m and more, the computational complexity for
tomographic reconstruction requires the use of highly efficient algorithms
in order to achieve reconstructions in the required timeframe of about 1ms.
This requirement led to the development of different new strategies, like
the Finite Element-Wavelet Hybrid Algorithm (FEWHA), which only needs
O (n) operations.

Figure 1: G. Auzinger. New Reconstruction Approaches in Adaptive Optics for Extremely Large Telescopes.PhD thesis, JKU Linz 2017
Figure 1, by Günter Auzinger: Schematic illustration of a laser
tomography adaptive optics (LTAO) system

A test case for all future Extremely Large Telescopes is the Keck All-sky Precision Adaptive-optics (KAPA). KAPA contains an LTAO module featuring 4 laser guide stars and will upgrade the Keck I telescope which is part of the W. M. Keck Observatory in Hawaii, see Figure 2. Since all previously performed studies for tomographic AO systems confirmed the good performance of FEWHA with synthetic data, we want to verify the quality of FEWHA with its tomographic capabilities on existing telescopes. Together with Microgate, a company in Bolzano, Italy, which will also construct the deformable mirror for the European Extremely Large Telescope, we plan to run FEWHA on the KAPA instrument. First tests in an software simulation environment with a KAPA setting are currently being prepared.

Figure 2: Keck Observatory in the U.S. state of Hawaii

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