Wave-front error breakdown in laser guide star multi-object adaptive optics validated on-sky by Canary

Monthly Notices of the Royal Astronomical Society

Morris

et al. 2019

Ground-based adaptive optics (AO) systems can use temporal control techniques to greatly improve image resolution. A measure of wind velocity as a function of altitude is needed to minimize the temporal errors associated with these systems. Spatio-temporal analysis of AO telemetry can express the wind velocity profile using the SLODAR technique. However, the limited altitude-resolution of current AO systems makes it difficult to disentangle the movement of independent layers. It is therefore a challenge to create an algorithm that can recover the wind velocity profile through SLODAR data analysis. In this study we introduce a novel technique for automated wind velocity profiling from AO telemetry. Simulated and on-sky centroid data from CANARY - an AO testbed on the 4.2 m William Herschel telescope, La Palma - is used to demonstrate the proficiency of the technique. Wind velocity profiles measured on-sky are compared to contemporaneous measurements from Stereo-SCIDAR, a dedicated high-resolution atmospheric profiler. They are also compared to European centre for medium-range weather forecasts. The software package that we developed to complete this study is open source.

Section: Wind Velocity Profiling From On-sky Ao Telemetrymentioning

confidence: 99%

Automated wind velocity profiling from adaptive optics telemetry

Laidlaw

Monthly Notices of the Royal Astronomical Society

Morris

et al. 2019

“…In this way, the optimal correction can be applied to one or more deformable mirrors to provide the best correction over a large field (see e.g. E-mail: sukanta.basu@gmail.com Vidal, Gendron & Rousset 2010;Gendron et al 2014;Martin et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Mesoscale modelling of optical turbulence in the atmosphere: the need for ultrahigh vertical grid resolution

Basu

Monthly Notices of the Royal Astronomical Society

et al. 2020

The high-fidelity modeling of optical turbulence is critical to the design and operation of a new class of emerging highly-sophisticated astronomical telescopes and adaptive optics instrumentation. In this study, we perform retrospective simulations of optical turbulence over the Hawaiian islands using a mesoscale model. The simulated results are validated against thermosonde data. We focus on turbulence in the free atmosphere, above the atmospheric boundary layer. The free-atmosphere is particularly important for adaptive optics performance and for sky coverage calculations and hence has significant impact on performance optimisation and scheduling of observations. We demonstrate that a vertical grid spacing of 100 m or finer is needed to faithfully capture the intrinsic variabilities of observed clear air turbulence. This is a particularly timely study because the next generation of Extremely Large Telescopes are currently under construction and their associated suite of instruments are in the design phase. Knowledge of the expected accuracy of optical turbulence simulations and real-time forecasts will enable the design teams to i) test and develop instrument designs and ii) formulate operational procedure.

“…relative positions of natural and laser guide stars (NGS/LGS), as well as the vertical optical turbulence profile. The profile, parameterised by the refractive index structure constant C 2 n (h), describes the distribution of turbulence as a function of altitude h. Imperfect tomographic reconstruction leads to tomographic error, which is common to all tomographic systems and forms a significant part of the total error budget Martin et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Limitations imposed by optical turbulence profile structure and evolution on tomographic reconstruction for the ELT

Farley

Monthly Notices of the Royal Astronomical Society

Morris

et al. 2020

The performance of tomographic adaptive optics systems is intrinsically linked to the vertical profile of optical turbulence. Firstly, a sufficient number of discrete turbulent layers must be reconstructed to model the true continuous turbulence profile. Secondly over the course of an observation, the profile as seen by the telescope changes and the tomographic reconstructor must be updated. These changes can be due to the unpredictable evolution of turbulent layers on meteorological timescales as short as minutes.Here we investigate the effect of changing atmospheric conditions on the quality of tomographic reconstruction by coupling fast analytical adaptive optics simulation to a large database of 10 691 high resolution turbulence profiles measured over two years by the Stereo-SCIDAR instrument at ESO Paranal, Chile. This work represents the first investigation of these effects with a large, statistically significant sample of turbulence profiles. The statistical nature of the study allows us to assess not only the degradation and variability in tomographic error with a set of system parameters (e.g. number of layers, temporal update period) but also the required parameters to meet some error threshold. In the most challenging conditions where the profile is rapidly changing, these parameters must be far more tightly constrained in order to meet this threshold. By providing estimates of these constraints for a wide range of system geometries as well as the impact of different temporal optimisation strategies we may assist the designers of tomographic AO for the ELT to dimension their systems.