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

Abstract

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.

Characterizing turbulence profile layers through celestial single-source observations

“…The median 35-layer model from the European Southern Observatory (ESO) [26,27] was used to parameterize the turbulence and wind speed profile for 256 Soapy simulations. This profile was selected to comply with previous publications [18,19] and because it derives from on-sky atmospheric profiles.…”

Compensation Techniques Aimed at Mitigating Vibrations in Optical Ground-Based Telescopes: A Systematic Review

“… We consider it extremely important to take into consideration the atmospheric data of the different sites in order to improve the adaptive optics systems by using the different atmospheric turbulence profiles. In this way, the systems would be calibrated according to the sky in which they operate [ 70 , 71 , 72 , 73 , 74 , 75 , 76 ]. Control applications also should be developed taking into account the particularities of each telescope and environment where it is currently operating.…”

Atmospheric turbulence profiling with multi-aperture scintillation of a Shack-Hartmann sensor

“…Imperfect prior information of the turbulence profile causes tomographic error, which accounts for a large fraction of the total AO error budget (Gilles et al 2008). Because atmospheric turbulence profile varies with time, tomographic reconstruction matrix should be updated in a timescale of tens of minutes, which corresponds to the typical time scale of the profile time evolution (Gendron et al 2014, Farley et al 2020.…”