The future generation of extremely large telescopes will be certainly equipped with wide-field adaptive optics systems. All the components of such adaptive optics systems have to be precisely specified, and most of the technical specifications are related to atmospheric turbulence parameters, particularly the profile of the refractive index structure constant Cn2(h). The monitor Profiler of Moon Limb (PML) for the extraction of the Cn2(h) profile with high vertical resolution for nighttime and daytime conditions by the observation of the moon limb or sun edge has been developed and is now routinely exploited at the Calern Observatory on the French Riviera. The PML instrument uses a differential method with two small subapertures through which the moon limb or sun edge are observed, leading to a continuum of double stars that allows a scan of the whole atmosphere with high resolution in altitude. The PML is an autonomous instrument aided by a set of equipment such as an all-sky camera, a small meteorological station, and an automatic system to cover the two subapertures with solar filters to switch from night/moon to day/solar observations. In addition, the PML instrument provides in real time a large characterization of the atmospheric turbulence since it can measure other turbulence parameters, such as the total seeing and the isoplanatic angle.

PML: a generalized monitor of atmospheric turbulence profile with high vertical resolution.

COupled SLope and scIntillation Detection And Ranging (CO-SLIDAR) is a recent profiling method of the vertical distribution of atmospheric turbulence strength ( Cn2 profile). It takes advantage of correlations of slopes and of scintillation, both measured with a Shack-Hartmann wavefront sensor on a binary star. In this paper, we present the improved CO-SLIDAR reconstruction method of the Cn2 profile and the first on-sky results of the CO-SLIDAR profiler. We examine CO-SLIDAR latest performance in simulation, taking into account the detection noise bias and estimating error bars along with the turbulence profile. The estimated Cn2 profiles demonstrate the accuracy of the CO-SLIDAR method, showing sensitivity to both low and high altitude turbulent layers. CO-SLIDAR is tested on-sky for the first time, on the 1.5 m MeO (Metrologie Optique) telescope at Observatoire de la Cote d’Azur (France). The reconstructed profiles are compared to turbulence profiles estimated from meteorological data and a good agreement is found. We discuss CO-SLIDAR’s contribution in the Cn2 profilers’ landscape and we propose some improvements of the instrument.

First on-sky results of the CO-SLIDAR C(2)(n) profiler.

Atmospheric turbulence reduces the image quality and resolution of ground-based optical telescopes. Future large solar telescopes (e.g. the CGST, China Giant Solar Telescope) should be equipped with adaptive optics (AO) systems. The design of AO systems is associated with atmospheric optical turbulence parameters, especially the profile of the refractive index structure C-n(2) (h). With the solar differential image motion monitor (S-DIMM) and the profiler of the moon limb (PML), a simplified version of a PML, termed a profiler of the differential solar limb (PDSL), was built in order to determine the daytime C-n(2) (h) and other atmospheric turbulence parameters. A PDSL with differential solar limb fluctuations was used to determine the turbulence profiling, and the extended solar limb extends the range of separation angles for a higher resolution of the height profile. The PDSL structure and its performance are described. In addition, numerical simulations were conducted to verify the effectiveness of the method. As revealed from the simulation results, the layered integral coefficient matrix is capable of solving the discretization error and enhancing the inversion accuracy of the turbulence contour. The first test results at Mt Wumingshan (a candidate site for the CGST) are presented.

Daytime optical turbulence profiling with a profiler of the differential solar limb

From its long expertise in Atmospheric Optics, the Observatoire de la Cote d'Azur and the J.L. Lagrange Laboratory have equipped the Calern Observatory with a station of atmospheric turbulence measurement (CATS: Calern Atmospheric Turbulence Station). The CATS station is equipped with a set of complementary instruments for monitoring atmospheric turbulence parameters. These new-generation instruments are autonomous within original techniques for measuring optical turbulence since the first meters above the ground to the borders of the atmosphere. The CATS station is also a support for our training activities as part of our Masters MAUCA and OPTICS, through the organization of on-sky practical works.

The Calern atmospheric turbulence station

The aim of this paper is twofold: (i) to deduce the most representative C2 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 C2 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.

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

Aims. Future extremely large telescopes will certainly be equipped with wide-field adaptive optics systems. The optimization of the performances of these techniques requires a precise specification of the different components of these AO systems. Most of these technical specifications are related to the atmospheric turbulence parameters, particularly the profile of the refractive index structure constantC 2 (h). A new monitor called Profiler of Moon Limb (PML) for the extraction of theC 2 N (h) profile with high vertical resolution and its first results are presented. Methods. The PML instrument uses an optical method based on the observation of the Moon limb through two subapertures. The use of the lunar limb leads to a continuum of double stars allowing a scan of the whole atmosphere with high resolution in altitude. Results. The first prototype of the PML has been installed at Dome C in Antarctica and the first results of the PML are presented and compared to radio-sounding balloon profiles. In addition to the C 2 (h) profile obtained with high vertical resolution, PML is also able to provide other atmospheric turbulence parameters such as the outer scale profile, the total seeing, and the isoplanatic and isopistonic angles.

/pdf/first-results-of-the-pml-monitor-of-atmospheric-turbulence-2ngjze17qy.pdf

First results of the PML monitor of atmospheric turbulence profile with high vertical resolution

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First results of the PML monitor of atmospheric turbulence profile with high vertical resolution