OPERA, an automatic PSF reconstruction software for Shack-Hartmann AO systems: application to Altair

Abstract

When doing high angular resolution imaging with adaptive optics (AO), it is of crucial importance to have an accurate knowledge of the point spread function associated with each observation. Applications are numerous: image contrast enhancement by deconvolution, improved photometry and astrometry, as well as real time AO performance evaluation. In this paper, we present our work on automatic PSF reconstruction based on control loop data, acquired simultaneously with the observation. This problem has already been solved for curvature AO systems. To adapt this method to another type of WFS, a specific analytical noise propagation model must be established. For the Shack-Hartmann WFS, we are able to derive a very accurate estimate of the noise on each slope measurement, based on the covariances of the WFS CCD pixel values in the corresponding sub-aperture. These covariances can be either derived off-line from telemetry data, or calculated by the AO computer during the acquisition. We present improved methods to determine 1) r 0 from the DM drive commands, which includes an estimation of the outer scale L 0 ; 2) the contribution of the high spatial frequency component of the turbulent phase, which is not corrected by the AO system and is scaled by r0. This new method has been implemented in an IDL-based software called OPERA (Performance of Adaptive Optics). We have tested OPERA on Altair, the recently commissioned Gemini-North AO system, and present our preliminary results. We also summarize the AO data required to run OPERA on any other AO system.

Numerical evaluation of an off-axis Point Spread Function reconstruction from the Woofer/Tweeter Adaptive Optics system

“…So far only one PSF reconstruction tool has been implemented for operational use on an astronomical telescope: Veran's [10,11] code for the Canada-France-Hawaii Telescope (CFHT) Adaptive Optics Bonnette (also called PUEO). Although the original method was developed using the curvature WFS, the algorithm was later adapted and applied to Shack Hartmann WFS (SH WFS) [12,13,14,15] . In the W/T AO Bench, the methodology is also applied to SH WFS [16] .…”

New algorithms for adaptive optics point-spread function reconstruction

“…Based on the Véran et al (1997) algorithm, PSF reconstruction has been developed for three AO systems, equipped this time with SH wavefront sensors, and tested during a few runs of observations, leading to good results: - Weiss (2003) has written a piece of PSF reconstruction software for ALFA (Kasper et al 2000), the SH AO system of the Calar Alto 3.5 m telescope; - Jolissaint et al (2004) has written OPERA, a piece of PSF reconstruction software for Altair (Herriot et al 2000), the 4-quadrant SH AO system of the Gemini North telescope; and - Fitzgerald et al (2004) have written a piece of PSF reconstruction software for the SH AO system of the UCO/Lick Observatory's 3 m Shane Telescope (Bauman et al 2002).…”

Online estimation of the wavefront outer scale profile from adaptive optics telemetry

“…It has been shown (Fusco 2000;Jolissaint, Veran & Marino 2004) that WFAO and PSF-R can be particularly sensitive to the global L 0 and therefore to its stratified version L 0 (h). Furthermore, the non-stationarity characteristics of turbulence require simultaneity in the estimation of C n 2 (h) and L 0 (h).…”