Optimizing the accuracy and efficiency of optical turbulence profiling using adaptive optics telemetry for extremely large telescopes. (arXiv:1901.05860v1 [astro-ph.IM])
<a href="http://arxiv.org/find/astro-ph/1/au:+Laidlaw_D/0/1/0/all/0/1">Douglas J Laidlaw</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Osborn_J/0/1/0/all/0/1">James Osborn</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Morris_T/0/1/0/all/0/1">Timothy J Morris</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Basden_A/0/1/0/all/0/1">Alastair G Basden</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Beltramo_Martin_O/0/1/0/all/0/1">Olivier Beltramo-Martin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Butterley_T/0/1/0/all/0/1">Timothy Butterley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gendron_E/0/1/0/all/0/1">Eric Gendron</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reeves_A/0/1/0/all/0/1">Andrew P Reeves</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rousset_G/0/1/0/all/0/1">Gérard Rousset</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Townson_M/0/1/0/all/0/1">Matthew J Townson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wilson_R/0/1/0/all/0/1">Richard W Wilson</a>
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.
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.
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