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Optimizing the accuracy and efficiency of optical turbulence profiling using adaptive optics telemetry for extremely large telescopes.

Laidlaw, Douglas J and Osborn, James and Morris, Timothy J and Basden, Alastair G and Beltramo-Martin, Olivier and Butterley, Timothy and Gendron, Eric and Reeves, Andrew P and Rousset, Gerard and Townson, Matthew J and Wilson, Richard W (2018) 'Optimizing the accuracy and efficiency of optical turbulence profiling using adaptive optics telemetry for extremely large telescopes.', Monthly notices of the Royal Astronomical Society., 483 (4). pp. 4341-4353.


Advanced adaptive optics (AO) instruments on ground-based telescopes require accurate knowledge of the atmospheric turbulence strength as a function of altitude. This information assists point spread function reconstruction, AO temporal control techniques and is required by wide-field AO systems to optimize the reconstruction of an observed wavefront. The variability of the atmosphere makes it important to have a measure of the optical turbulence profile in real time. This measurement can be performed by fitting an analytically generated covariance matrix to the cross-covariance of Shack–Hartmann wavefront sensor (SHWFS) centroids. In this study we explore the benefits of reducing cross-covariance data points to a covariance map region of interest (ROI). A technique for using the covariance map ROI to measure and compensate for SHWFS misalignments is also introduced. We compare the accuracy of covariance matrix and map ROI optical turbulence profiling using both simulated and on-sky data from CANARY, an AO demonstrator on the 4.2 m William Herschel telescope, La Palma. On-sky CANARY results are compared to contemporaneous profiles from Stereo-SCIDAR – a dedicated high-resolution optical turbulence profiler. It is shown that the covariance map ROI optimizes the accuracy of AO telemetry optical turbulence profiling. In addition, we show that the covariance map ROI reduces the fitting time for an extremely large telescope-scale system by a factor of 72. The software package we developed to collect all of the presented results is now open source.

Item Type:Article
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Publisher statement:© 2018 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.
Date accepted:27 November 2018
Date deposited:24 January 2019
Date of first online publication:03 December 2018
Date first made open access:24 January 2019

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