Effects of wind velocity profiles on turbulence-induced quasi-static aberrations

Polly Gill; Tim Butterley; Tim Morris

doi:10.1117/12.2628911

29 August 2022 Effects of wind velocity profiles on turbulence-induced quasi-static aberrations

Polly Gill, Tim Butterley, Tim Morris

Proceedings Volume 12185, Adaptive Optics Systems VIII; 121855S (2022) https://doi.org/10.1117/12.2628911
Event: SPIE Astronomical Telescopes + Instrumentation, 2022, Montréal, Québec, Canada

Conference Poster

Abstract

Quasi-static aberrations are wavefront distortions that vary on a timescale longer than that typically controlled by the adaptive/active control loops used to maintain the image quality within a large telescope. The source of these errors can be due to gravitational or thermal flexure of the telescope or poorly averaged atmospheric turbulence residuals. Following the method of Gordon et al,¹ a simulation was used to explore the averaging rate of atmospheric turbulence residuals for a phase screen translating across the telescope aperture. In line with Gordon et al, the RMS of azimuthally averaged Zernike modes decreases with exposure time, approximately as a −0.5 power law. However, our model shows that there is a significant deviation in the power law exponent between individual modes within the same azimuthal pair. For example, for a 39 m telescope (Fried parameter of 0.14 m and outer scale of 39 m and a wind speed of 10 m/s) the times taken for Zernike modes 5 and 6 (in Noll’s scheme) to reach a residual error of λ/20 are 10 and 64 seconds in the K-band and 40 and 1016 seconds in the V-band respectively. Crucially, the rate at which the individual modes average out is dependent upon wind direction, meaning that both the C²_n and wind velocity profiles can have a large effect on the modal variance of observed quasi-static aberrations. We discuss the impact of variations in wind velocity profile on active optics and adaptive optics performance.

Citation Download Citation

Polly Gill, Tim Butterley, and Tim Morris "Effects of wind velocity profiles on turbulence-induced quasi-static aberrations", Proc. SPIE 12185, Adaptive Optics Systems VIII, 121855S (29 August 2022); https://doi.org/10.1117/12.2628911

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