Common menu bar links
Related Information
Institutes & Programs
Areas of Research
Communities
Careers
News
Events
Project Leader
Kei Szeto
Phone: 250-363-0059
Fax: 250-363-0045
Email: Kei.Szeto@nrc-cnrc.gc.ca
Gemini [GLAO] Ground Layer Adaptive Optics
The basic goal of this feasibility study is to determine how best to provide adaptive-optics compensated images over a large 10 arcminute field for present and future Gemini instruments. This study, led by NRC-HIA, is a collaborative effort between NRC-HIA and the Universities of Arizona and Durham.
Project Engineer: Kei Szeto
Project Scientist: Dave Andersen
Technical overview
Atmospheric turbulence generated near the ground (plus wind shake and telescope vibration) will negatively impact the delivered image quality. Because these distortions on the incoming wavefront will be common over a large solid angle, it has been suggested that a ground layer adaptive optics (GLAO) system could correct these wavefront errors and deliver an improved, uniform point spread function over a very large field of view.
As part of an instrument feasibility study for the Gemini Observatory, we have undertaken an extensive modeling effort to understand the expected gains of a GLAO system and explore various performance trades. We found that the diameter (FWHM) of a PSF that has been corrected by GLAO will decrease by at least 0.1 arcsec, which in turn will shorten typical exposure times by up to 50%. Moreover, unlike traditional AO systems which operate only in conditions with already good image quality, GLAO produces the greatest relative gains when the seeing is worst; this dramatically reshapes the integrated image quality distribution at a telescope site and does away with "bad seeing" (see Figure).
As part of the feasibility study, we proposed a GLAO system consisting of four comparatively low power laser guide stars, an adaptive (deformable) secondary mirror, and a new Gemini Acquisition and Guide Unit complete with GLAO wavefront sensors. Our proposed GLAO system will therefore act as a telescope upgrade; it will deliver improved image quality to all existing and future Gemini instruments.
Current status
A site testing campaign was undertaken at Mauna Kea and 20,000 SLODAR (Slope Detection and Ranging) profiles were taken. Results were very encouraging; roughly half of the turbulence is within the first 70 m above Gemini-N. Simulations of all these profiles using PAOLA are shown in the Figure. We are awaiting action by Gemini to start a conceptual design study of GLAO.
Figure: Integrated image quality (measured in FWHM) with (solid line) and without (dashed) a GLAO correction based on 20,000 SLODAR profiles (data from M. Chun and R. Wilson).
Related links
The following hyperlinks are to sites of organizations or other entities that are not subject to the Official Languages Act. The material found there is therefore in the language(s) used by the sites in question.
Ces hyperliens donnent accès à des sites d'organismes qui ne sont pas assujettis à la Loi sur les langues officielles. L'information qui s'y trouve est donc dans la langue du site.
|
|
|
|
|
|
|
|
