experimental results of tomographic reconstruction on onera laboratory wfao bench
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Experimental results of tomographic reconstruction on ONERA laboratory WFAO
bench
A. Costille*, C. Petit*, J.-M. Conan*, T. Fusco*, C. Kulcsár**, H.-F. Raynaud**
*ONERA, DOTA – Unité HRA, Châtillon** L2TI, Université Paris 13, Villetaneuse
Anne.costille@onera.fr
AO4ELT – 26/06/09 – A. Costille
Overview
I. Context
II. WFAO laboratory test bench at ONERA: HOMER
III. Experimental validation of Wide Field AO (WFAO) concepts in closed-loop
IV. Conclusion and perspectives
AO4ELT – 26/06/09 – A. Costille3
I. Context
• AO is limited by the anisoplanatism effect• Development of new WFAO concepts (LTAO and MCAO) and first
instruments:• Multi-analysis• Tomographic reconstruction• New control laws
• Theoretical studies are mature but need for experimental validations
• Development of a WFAO bench HOMER:• Study and comparison of WFAO concept
• Calibration• Field aberrations (WFS and Imaging path) • Model identification for control laws implementation
• Development of new concepts• Comparison of control laws
• Classic control: least-square + integrator• LQG control:
• Estimation and prediction of the turbulent volume, based on a Kalman filter• Projection of the estimated turbulence
Context - HOMER bench – Experimental results - Conclusion
AO4ELT – 26/06/09 – A. Costille
Light source with reconfigurable positions of laser
Ground layer DM (52 actuators, ALPAO
technology)
Second DM (88 actuators, ALPAO
technology)
Wide Field WFS (1002x1004
pixels)
ANDOR EMCCD
Visible Imaging camera (1024x1024
pixels)
7x7 microlens array
Manufactured at ONERA
F = 30mm - dμl = 1.1mm
RTC PC-linux
Shaktiware
λ = 635 nm
Fs < 25 Hz
1. Experimental setup of HOMER benchContext - HOMER bench – Experimental results - Conclusion
4
AO4ELT – 26/06/09 – A. Costille5
2. Specificities and equations of the system• Turbulence
• Generated by the DMs with turbulent voltages v : φtur = Nturv• Where Ntur is the influence matrices of DM52 and DM88, φtur the turbulent phase
• Turbulence model: AR1 type : vn+1 = Avvn + bv
• WF Sensing • Measurement equation in AO : sn = Dφ + w
s: slopes, D: WFS model, φ: measured phase, w: measurement noise
• Measurement equations for several directions : sn = DMαφ + w
• Where Mα is the matrix of the projection of the phase in the pupil in directions α
• On HOMER : one wide field Shack-Hartmann (142x142 pixels / sub-aperture)
Context - HOMER bench – Experimental results - Conclusion
• 3 WFS on NGS of 16x16 analysis area• Configuration and number of GS modifiable
• Correction phase φcor = Nu• Where N is the influence matrices for correction DM (DM52 in LTAO, DM52 +
DM88 in MCAO)• u the correction voltages
AO4ELT – 26/06/09 – A. Costille
3. Control laws equations
• Integrator control : least-square reconstructor + integrator
• Control equation : un+1 = un + G yn = un + g Mcom sn
• Where g is the integrator gain, Mcom the control matrix : generalized inverse of interaction matrix Mint = DMαN
• LQG control
• Where is the estimated phase in Zernike basis• Atur is the turbulence transition matrix• Hopt is the Kalman Gain
• P = fct(Mβ, N) the projector of the estimated phase on the DM for correction (β correction directions)
Context - HOMER bench – Experimental results - Conclusion
nnn
nntur
nn
nnnnoptnnnn
Pu
A
NuDMDMyH
/1
//1
21/11//
ˆ
ˆˆ
ˆˆˆ
6
AO4ELT – 26/06/09 – A. Costille
3. Control laws equations
• Integrator control : least-square reconstructor + integrator
• Control equation : un+1 = un + G yn = un + g Mcom sn
• Where g is the integrator control, Mcom the control matrix : generalized inverse of interaction matrix Mint = DMαN
• LQG control in the DM space
• Where is the estimated voltages• Av is the turbulence transition matrix• Hopt is the Kalman Gain
• P = fct(Mβ, D, N) the projector. In MCAO : P = Id
• Control laws applied with the RTC (Shaktiware)
Context - HOMER bench – Experimental results - Conclusion
nnn
nnv
nn
nnntur
noptnnnn
vPu
vAv
NuDMvNDMyHvv
/1
//1
21/11//
ˆ
ˆˆ
ˆˆˆ
v
7
Interaction matrices
AO4ELT – 26/06/09 – A. Costille8
1. Experimental Conditions
• Turbulent profile• Turbulent layers conjugated with the DMs• Cn2 = 50% in each layer• D/r0 = 7 (global in the pupil)
• WFS on 3 NGS in HOMER FoV• WFS- Imaging field : 420 x 361 λ/D ( i.e. 81’’x 70,4’’ equivalent 8 m telescope)
• Representation of anisoplanatism effect for a 8 meter telescope• Conservation of the angular separation of the footprint in altitude• For D = 8m, FoV = 2’, h = [0,13800]m
• No correction of the non common path aberrations• Impact of the the non common path aberrations :
• 65% of SR on axis, without turbulence• Variation of the SR in the FoV < +/-5 %
Context - HOMER bench – Experimental results - Conclusion
AO4ELT – 26/06/09 – A. Costille9
2. Calibration aspects
Context - HOMER bench – Experimental results - Conclusion
• Model identification for LQG control in DM space• Models of the DMs, of the WFS, of the projector : calibration of interaction matrices• Model of the turbulence, measurement noise
• Relative positions of the WFS in the FoV• Determination of the theoretical positions of the GSs with astrometry• Presence of distortion on the optical path = Deformation of the GS configuration
• Errors in astrometry• Errors on the directions of the WFS• Distortion in the optical path
• Correction of this distortion by our system not possible• Solution: correction of astrometry to take distortion into account
1 sub-pupil of HOMER
1 WFS (real case)
Position in the FoV (δ)P
osi
tion
in t
he
Fo
V (
δ)
0.34
0
-0.34
0.34-0.34 0
PSFs with astrometry
Position dans le champ (δ)
Po
sitio
n in
th
e F
oV
(δ)
0.34
0
-0.34
0.34-0.34 0
PSFs after correction of astrometry
AO4ELT – 26/06/09 – A. Costille10
3. Experimental results in WFAO
• SR open-loop : 7% (average)• SR in classic AO
• On axis : 65% and in the border : 12% (anisoplanatism)
• SR in MCAO• SR closed-loop : 56 % (average in the FoV)
Po
sitio
n in
th
e F
oV
(δ
)
0.34
0
-0.34
Position in the FoV (δ)0.34-0.34 0 0.34-0.34 0 0.34-0.34 0
No correction AO correction MCAO correction
Position in the FoV (δ) Position in the FoV (δ)
Context - HOMER bench – Experimental results - Conclusion
65%
55% 58%
62%
AO4ELT – 26/06/09 – A. Costille11
3. Experimental results in WFAO
• MCAO results:• Slightly better performance with LQG control
• Mean SR – integrator : 53% - LQG : 56%• Turbulence generated by DMs : very favorable for integrator control law
• Good agreement between numerical and experimental results
• LTAO results:• Test with LQG control• Tomographic reconstruction of the turbulence proven (results close to AO case)• Test of tomographic reconstruction according to
• The number of GSs• The position of the GSs
Context - HOMER bench – Experimental results - Conclusion
Position in the FoV (δ)
Pos
ition
in t
he F
oV (
δ)
200
0
-200
200-200 0
55%
LTAO
AO4ELT – 26/06/09 – A. Costille1212
Conclusion
• HOMER is operational in AO, LTAO and MCAO• First experimental validations
• Of closed-loop LTAO• Of LQG control for WFAO systems (LTAO and MCAO)
• Study of the LQG control in WFAO• Gain in performance proven with LQG control• Preliminary studies of model identifications issues and impact of model
errors
• Problems of relative positions of WFS in the FoV• Distortion effect to take into account (not corrected by the system)• Numerical studies on HOMER and VLT case on going
Context - HOMER bench – Experimental results - Conclusion
AO4ELT – 26/06/09 – A. Costille1313
Perspectives
70 %
70 %
70 %
50 % 60 %
70 %
70 %
70 %
• Integration of a turbulent module (summer 2009)• Calibration of the turbulence• Study of control laws in real conditions and comparison of sub-optimal control
laws (POLC…)• Problems of model identification with LQG control
• Choice of the estimation basis• Turbulent model• Calibration of the models of the system components
• Calibration issues for WFAO systems:• Field aberrations in the imaging path• Problems of the relative position of the WFS in the FoV
• Study of LGS :• WFS and control strategy on both LGS and NGS
• Multi-stage WF sensing (additional WFS after the ground DM52)
• HOMER web site : http://www.onera.fr/dota/homer
Context - HOMER bench – Experimental results - Conclusion
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