AO4ELT 2

Analysis of Ground Layer Turbulence Profiles at CTIO and Mauna Kea

Ronald GAGNE — 2011-08-19T10:09:58Z

Submitted by R. Gagné

Authors

Ronald Gagné, Paul Hickson, Thomas Pfrommer, Masen Lamb, Marc Baril

Affiliations

University of British Columbia

Abstract

For the past 4 years high-resolution ground layer turbulence measurements have been carried out on Cerro Tololo Inter-American Observatory (CTIO) with a lunar scintillometer. We present C_N2-profiles in the range up to 1 km and seeing statistics from fall 2007 to spring 2011. Comparisons with weather parameter links local topography to optical turbulence. The observations in Chile are compared to a ground-layer study on Mauna Kea at the Canada France Hawaii Telescope by the use of median seeing values as well as scale heights derived from the turbulence integral.

The vibration compensation system for ARGOS

Diethard PETER — 2009-02-28T23:00:00Z

Submitted by Diethard PETER

Authors

D.Peter, W. Gaessler, J. Borelli, M. Kulas

Affiliations

Max-Planck-Institut fuer Astronomie

Abstract

For every adaptive optics system telescope vibrations can strongly reduce the performance. This is true for the receiver part of the system i.e. the telescope and wave front sensor part as well as for the transmitter part in the case of a laser guide star system. Especially observations in deep fields observed with a laser guide star system without any tip-tilt star will be greatly spoiled by telescope vibrations. The ARGOS GLAO system actually being built for the LBT aims to implement this kind of mode where wave front correction will rely purely on signals from the laser beacons. To remove the vibrations from the uplink path a vibration compensation system will be installed. This system uses accelerometers to measure the vibrations and corrects their effect with a small fast tip-tilt mirror. The controller of the system is built based on the assumption that the vibrations take place at a few distinct frequencies. Here I present a lab set-up of this system and show first results of the performance.

Monitoring of the atmospheric turbulence profiles for thespecification of ELTs adaptive optics systems

Aziz ZIAD — 2009-02-28T23:00:00Z

Submitted by Aziz ZIAD

Authors

Aziz Ziad, Julien Borgnino, François Martin, Jérôme Maire, Erick Bondoux, Jean-Baptiste Daban, Richard Douet, Yan Fanteï-Caujolle et Alex Robini

Affiliations

Laboratoire H. Fizeau-UMR 6525 Université de Nice Sophia Antipolis

Abstract

The futures large telescopes will be certainly equipped with Multi-Conjugate Adaptive Optics systems. The optimization of the performances of these techniques requires a precise specification of the different components of these systems. Major of these technical specifications are related to the atmospheric turbulence particularly the structure constante of the refractive index Cn2 and the outer scale L0. New techniques for the monitoring of the Cn2 and L0 profiles with high vertical resolution will be presented.

Cn2 profilometry from Shack-Hartmann data: model and experiment

Juliette VOYEZ — 2009-02-28T23:00:00Z

Submitted by Juliette VOYEZ

Authors

J. Voyez, C. Robert, N. Védrenne, B. Fleury, V. Michau, T. Fusco

Affiliations

ONERA

Abstract

The design phase for the Wide Field Adaptive Optics (WFAO) systems for the ELTs has started. LTAO (ATLAS), MCAO (MAORY) and MOAO (EAGLE) approaches have been studied for the E-ELT. All these systems have in common a need for a precise tomographic reconstruction of the turbulent volume. In that frame, the Cn2 structure, representing the turbulence strength, becomes a critical parameter for the final tomographic reconstruction performance. Getting of high-resolution Cn2 profiles is then a crucial point for the design of E-ELT AO systems. In this context, we have proposed a new profilometry method using Shack-Hartmann (SH) data. Slopes and scintillation indexes being recorded simultaneously with a Shack-Hartmann wavefront sensor (SHWFS), their correlation is exploited in order to retrieve the Cn2 profile. This method, named CO-SLIDAR (COupled Slope and scIntillation Detection And Ranging), uses correlation of SHWFS data from two separated stars. CO-SLIDAR has been validated in numerical simulations in a precedent work. The next step is an on-sky validation with a full-dedicated SHWFS, to measure a Cn2 profile with 40 layers, up to 20 km of altitude, with a 500m altitude resolution. The system will be set up on a 1.5m telescope. Here, we first expound the theoretical background of SH data and CO-SLIDAR processing. The Cn2 profile is estimated by minimizing a maximum likelihood criterion under positivity constraint. Then, we describe the experimental system and the future on-sky experiment. Determination of outer scale L0 with CO-SLIDAR, taking advantage of the large telescope diameter, is investigated.

Vibration characterization and mitigation at the Gemini-South telescope

Andres GUESALAGA — 2009-02-28T23:00:00Z

Submitted by Andres GUESALAGA

Authors

Ignacio Rodriguez(1), Benoit Neichel(2), Markus Hartung(2), Thomas Haywards(2), Julian Christou(3), Francois Rigaut(2), Dani Guzman(1), Andres Guesalaga(1)(*)

Affiliations

(1)Pontificia Universidad Católica de Chile, 4860 Vicuna Mackenna, Casilla 7820436, Santiago, Chile (2)Gemini Observatory Southern Operations Center, Colina el Pino s/n, Casilla 603, La Serena, Chile (3)Gemini Observatory Northern Operations Center, 670 N. A'Ohoku Place, Hilo HI 96720, USA (*) corresponding author: aguesala@ing.puc.cl

Abstract

This paper describes a vibration analysis carried out at the Gemini South telescope for several observation instruments, namely: Canopus, NICI, GSAOI and P2 (a peripherical WFS used for telescope guiding). The aim is to find the origins of these disturbances and possible ways to mitigate them. The analysis has shown that common vibration patterns can be identified; however they differ in terms of spike broadness, direction and modes affected. Based on these data, two types of controllers (Kalman and infinity) were designed with a particular emphasis on stability and robustness, especially under uncertainty in some of the loop components. From an analysis of the real open-loop data obtained from the instruments, we demonstrate that these controllers would provide a substantial improvement compared to standard integrator controllers in terms of vibration rejection and Strehl ratio. We recently implemented a Kalman controller for the Canopus Tip/Tilt loop. The first results obtained with this controller will be presented as well.