First on-sky SCAO validation of full LQG control with vibration mitigation on the CANARY pathfinder

Abstract

Adaptive optics provides real time correction of wavefront disturbances on ground based telescopes. Optimizing control and performance is a key issue for ever more demanding instruments on ever larger telescopes affected not only by atmospheric turbulence, but also by vibrations, windshake and tracking errors. Linear Quadratic Gaussian control achieves optimal correction when provided with a temporal model of the disturbance. We present in this paper the first on-sky results of a Kalman filter based LQG control with vibration mitigation on the CANARY instrument at the Nasmyth platform of the 4.2-m William Herschel Telescope. The results demonstrate a clear improvement of performance for full LQG compared with standard integrator control, and assess the additional improvement brought by vibration filtering with a tip-tilt model identified from on-sky data, thus validating the strategy retained on the instrument SPHERE at the VLT.

Monte Carlo modelling of multi-object adaptive optics performance on the European Extremely Large Telescope

“…Therefore the results given at lower frame rates are likely to be more optimistic, since lower frame rates will suffer more from uncorrected vibrations, even when vibration mitigation techniques, such as linear-quadratic-gaussian (LQG) control, are used (Sivo et al 2014). Higher order vibrational modes can be compensated using LGS measurements.…”

Kalman Filter Based Optimal Controllers in Free Space Optics Communication

“…On the assumption that both the delay in WFS measurement and the DM response is in one time interval T  , the measurement equation averaged over one time interval can be written as [1,[20][21][22][23][24][25] …”

“…However, in our study, we focus on the various Kalman filters in an AO system with the models more conveniently given in [1,[20][21][22][23][24]. A closedloop control law resulting from a global optimization is proposed in [20] to demonstrate the efficiency in the context of multi-conjugate adaptive optics (MCAO).…”

“…Actually, a convenient framework for the analysis of AO controllers is provided in [1] with an implicit phase turbulence model. Based on the framework, some interesting experimental studies are also given in [21][22][23][24], for example, vibrations, windshake, and tracking are considered in [21,22,24] which illustrate the experimental validation of the control law that LQG can provide an optimal correction of the vibrations in the case of residual phase minimal variance. The method with experimental proof in [23] is fundamentally the same as that in [1].…”

“…The effective framework in [1,[20][21][22][23][24] is based on a linear description of constitutive elements of an AO loop through the combination of Kalman filter and LQ (state feedback) to produce input signals for DM. This paper extends Caroline Kulcsár's works and presents the performance of Kalman filter and its variants in classic discrete-time linear AO systems.…”