Anisoplanatic error evaluation and wide-field adaptive optics performance at Dome C, Antarctica

Abstract

The aim of this paper is twofold: (i) to deduce the most representative C 2 N profile(s) for Dome C (DC), Antarctica, from the latest measurements, and (ii) to evaluate the performance of a widefield adaptive optics (AO) system equipping a 2-3 m telescope. Two models of the C 2 N profile, corresponding to the bimodal distribution of seeing (a poor seeing mode and a good seeing mode), are composed from both Single Star Scidar data and balloon radio soundings. The anisoplanatic error is first evaluated for a standard AO system from Monte Carlo simulations. DC is shown to outperform Mauna Kea for both seeing modes. A simple ground-layer AO (GLAO) system is then considered. This provides an anisoplanatic error of less than 150 nm over a field of 30 arcmin for the good seeing mode, corresponding to a basic performance Strehl ratio (considering also the fitting and the servo-lag errors) of more than ∼80 per cent in K and ∼50 per cent in J. The poor seeing model shows performance comparable to the Mauna Kea model. We also studied the influence of telescope elevation, showing that a telescope at 40 m would perform, in the poor seeing mode, like a telescope observing 8 m above the ground in the good seeing mode. Finally, we show that while tip-tilt-only correction permits high levels of correction in the good seeing mode at 40 m, it is not as efficient as the GLAO system, even at an altitude of 8 m, and it is not sufficient for high levels of correction for poor seeing, even at a height of 40 m.

Compressive Shack-Hartmann Wavefront Sensor based on Deep Neural Networks

“…Besides, the compressive Shack-Hartmann wavefront sensing algorithm can reduce the requirement of brightness of guide stars in an adaptive optics system. Wide field adaptive optics system, such as ground layer adaptive optics system could then use natural guide stars as wavefront references for observations (Rigaut 2002;Nicolle et al 2004b;Travouillon et al 2004;Chun et al 2016;Carbillet et al 2017;Jia et al 2018;Lu et al 2018b). In our future works, we will integrate the CS-WFS with the deep learning based PSF model (Jia et al 2020) to develop high-order PSF reconstruction method and we will also further investigate applications of the compressive wavefront sensing in wide field adaptive optics systems.…”

Dome C coherence time statistics from DIMM data

“…Combined to low seeing values around 0.4 arcsec, this offers interesting perspective for high angular resolution solar imaging and solar adaptive optics (AO). Indeed a large coherence time reduces the delay error of an AO system, while a small seeing value allows to benefit from a good correction [23,24].…”

Turbulence monitoring at the Plateau de Calern with the GDIMM instrument

“…seeing, isoplanatic angle, coherence time and outer scale. The 3 first quantities are of fundamental importance for adative optics (AO) correction: a large coherence time should allow to reduce the delay error, a small seeing value to easily close the loop and benefit from a rather good correction, and a large isoplanatic angle to reduce the anisoplanatic error, enlarge the sky coverage and allow very wide fields of correction (see [ [20]] and references therein). Indeed several projects regarding adaptive optics systems are planned at the MeO and C2PU [21] telescopes and they will benefit of the data given by the CATS station.…”