Statistics of turbulence parameters at Maunakea using the multiple wavefront sensor data of RAVEN

Abstract

Prior statistical knowledge of the atmospheric turbulence is essential for designing, optimizing and evaluating tomographic adaptive optics systems. We present the statistics of the vertical profiles of C 2 N and the outer scale at Maunakea estimated using a Slope Detection And Ranging (SLODAR) method from on-sky telemetry taken by RAVEN, which is a MOAO demonstrator in the Subaru telescope. In our SLODAR method, the profiles are estimated by a fit of the theoretical auto-and cross-correlation of measurements from multiple Shark-Haltmann wavefront sensors to the observed correlations via the non-linear Levenberg-Marquardt Algorithm (LMA), and the analytic derivatives of the spatial phase structure function with respect to its parameters for the LMA are also developed. The estimated profile has the median total seeing of 0.460 and large C 2 N fraction of the ground layer of 54.3 %. The C 2 N profile has a good agreement with the result from literatures, except for the ground layer. The median value of the outer scale is 25.5 m and the outer scale is larger at higher altitudes, and these trends of the outer scale are consistent with findings in literatures.

Off-axis point spread function characterization in laser guide star adaptive optics systems

“…Because we know the exact binary parameters, we can estimate how we deviate from those regarding the PSF model. Particularly the photometry error is given by ∆mag = −2.5 × log 10 ∆F ∆F 0 (34) while the astrometry error results from…”

“…Such models exist in the literature, but are either not laser-compliant [50,37,24], or not numerically efficient [19,3,13], particularly for future AO systems on next 40 m class telescopes with large number of degrees of freedom. The C 2 n (h) profile is accessible either from internal methods handling AO telemetry of multiple guide-stars [34,30,23], or from external profilers [53,48,36,35] or more recently from meso-scale models [31]. For single guide-star AO systems, the C 2 n (h) is not measurable from AO telemetry, calling for external profilers for modelling the off-axis PSF.…”

“…For single guide-star AO systems, the C 2 n (h) is not measurable from AO telemetry, calling for external profilers for modelling the off-axis PSF. However, studies [34] have highlighted discrepancies on the retrieved profile by comparing outputs of external to internal profiling techniques. Consequently, using an external C 2 n (h) profile along a likely different line-of-sight from the observations might degrade the accuracy of PSF modeling.…”

PEPITO: atmospheric Profiling from short-Exposure focal Plane Images in seeing-limiTed mOde

“…At present, profiling using AO instruments is performed from the cross-correlation of Wave-Front Sensor (WFS) measurements (Laidlaw et al 2018;Mazzoni et al 2016;Ono et al 2017;Martin et al 2016;Neichel et al 2014;Vidal et al 2010), with profile height limits of ∼ 10-20 km imposed principally by the telescope diameter, and then additionally the cone effect for laser-based AO (Foy 2000). However, such an approach is only available on multiple GSbased systems and can not be deployed to predict PSF variations on images delivered by single-conjugated AO systems.…”

Estimation of atmospheric turbulence parameters from Shack–Hartmann wavefront sensor measurements

“…The use of AO telemetry for atmospheric turbulence sensing is not new (e.g. Schöck et al 2003;Fusco et al 2004;Jolissaint et al 2018) for single-sensor telemetry and (Guesalaga et al 2017;Ono et al 2017) for multiple sensor telemetry. The common approach to estimate turbulence parameters from a single SH-WFS data uses the projection on Zernike polynomials of the wavefront phases reconstructed from the telemetry data -wavefront phase gradient measurements and deformable mirror commands.…”