micro-arcsec mission:
DESCRIPTION
Micro-Arcsec mission: implications of the monitoring , diagnostic and calibration of the instrument response in the data reduction chain. Deborah Busonero – INAF OATo. & the OATo Team. Corcione L.,Gai M.,Gardiol D.,Lattanzi M.G.,Loreggia D.,Riva A.,Russo F. - PowerPoint PPT PresentationTRANSCRIPT
Micro-Arcsec mission:implications of the monitoring,
diagnostic and calibration of the instrument response
in the data reduction chain
7 maggio 2009
Deborah Busonero – INAF OATo
D. Busonero - Osservatorio Astronomico di Torino
Corcione L.,Gai M.,Gardiol D.,Lattanzi M.G.,Loreggia D.,Riva A.,Russo F.
& the OATo Team
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Instrument monitoring and diagnostic are fundamental to fullfill the astrometric accuracy goal of the 21° century astrometry space mission
Different approach to perform the instrument monitoring and diagnostic:
SIM - Lite Gaia
Scanning mode Pointing telescope
No measurements correlation Spatial correlation among the measurements
Self-calibrated system closure condition
Instrument health checkand monitoring via hardware
o minimize correlationso hardware cost
Measure equations Image location (the observable) as function of several parameters
O = f (S, A, C) + n
Huge number of unknowns
SIM - Lite Gaia
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Astrometric solution for Gaia: Formulation
From L. Lindegren
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The problem: reduction of the numbers of the instrumental calibration parameters
• The basic measurement is the "time of observation" for each star's crossing a CCD 10^12 measurements in total
• Unknown parameters to estimate:– 5 astrometric parameters per star– attitude (celestial orientation) of instrument as function of time– instrument calibration parameters (basic angle, CCD positions, etc)– possibly additional parameters (incl. PPN-γ) 5×10^9 unknowns in total•Not all stars are suitable for simple modelling (binaries, etc)– a subset of "primary stars" is used for the astrometric solution: 100 million primary stars (10% of all)
astrometric solution needs 5×10^8 unknowns
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Needs procedures and tools for instrument diagnostic and calibration with the goal to decrease the parameter space and solve degenerations.
Variation of the instrumental response over the field, with wavelength
and in time, are potentially critical. Appropriate modelling of the
astrometric response is required for optimal definition of the data
reduction and calibration algorithms, in order to ensure high sensitivity
to the astrophysical source parameters and in general high accuracy.
The measured signal profile is affected by optics, attitude, detector
response and operations.
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From B. Holl
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Data Reduction Principles
Sky scans(highest accuracy
along scan)
Scan width: 0.7°
1. Object matching in successive scans2. Attitude and calibrations are updated3. Objects positions etc. are solved4. Higher terms are solved5. More scans are added6. System is iterated
Pre-launch phase (end of 2011) selection of those parameters which have an impact (related to optics, attitude, detector response and operations) on the accuracy performance, analysis of the critical aspects for the formulation of the calibration models; (forward analysis)
Commissioning phase, during which the nominal values of the parameters are validated and, if necessary, updated;
Operations phase, during which the data will be acquired and processed for the instrument monitoring and for the improvement of the calibration models developed in the previous phases.backward analysis: inverse problem of disentangling both astrophysical and instrumental parameters from the set of science and auxiliary data
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Due to: Temperature variation during a lunar eclipse Something happened difetto to the electronics (irregolar power supply)
What to do? Variation of the orbit or new assessment of the alectronicsIn the case it is a permanent variation we will need to refocus the telescope.
Focal length common mode variation and CCD displacement .
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Cromatic displacement for Astro 1
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Cromatic displacement for Astro 2
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Field distortion (due to optics)
See also D.Busonero et al. A&A 2006
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Field distortion (due to CTIs)
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Remarks:- transmission variation can be minimised by design and construction;- it can be monitored by suitable pupil imaging devices (e.g. WFS);- it cannot be identified by point-to-point measurements
GAIA-C3-TN-INAF-MG-008 M.Gai, D. Busonero
Astrometric effects of non-uniform telescope throughput
In real telescopes, the optical parameters evolve with time, and the degrada-tion is often not uniform.
variations in the image profile photo-centre displacements result in astrometric errors.
Need mitigation techniques applicable from design stage to calibrations.
Patch induced photo-centre displacement
[m]
[m
]
-0.5 0 0.5
-0.2
0
0.2 -5
0
5Photo-centre displacement:
Mean: 0.033 as
RMS: 3.341 as
PTV: 14.131 as (Potential) astrometric error depending on patch position
Reversing the aberrations and WFE map (specular PSF):
[m]
[m
]
-0.5 0 0.5
-0.2
0
0.2 -5
0
5Opposite photo-centre displacement for given opacity patch position
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Remarks on overall instrument
Throughput variations independent on each telescope [at least on non-common path, from M1 to M4]
Time evolution may be different [e.g. different cross section, due to orientation, to individual solar flares]
Transmission distribution could be deduced e.g. from WFS, albeit at low resolution, if read throughout the mission [impact on operations]
Global throughput may be monitored by (averaged) photometric information (RBP, BBP, but also AF)
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PSF/LSF modelling for PSF/LSF calibration
From experiments with “laboratory” CCD data we found:•Bi-quartic spline sufficiently flexible to give good fit everywhere•Residuals fully consistent with expected noise•Tendency to oscillation in wings can be removed by smoothing constraint (difficult) or adding Lorentzian wings (easy, and gives good extrapolation)
BUT: – spline representation requires many parameters (~35) – probably too detailed at ±3-8 samples from centre – transition from spline to Lorentzian is rather abrupt
We need to find a model with (much) reduced dimensionality (work in progress)
The astrometric performance of astronomical instruments is related to the image profile (Point Spread Function - PSF)
A complete PSF/LSF analytical modelling is fundamental to reach the accuracy target level
Preliminary study: GAIA-C3-TN-INAF-MG-007 M. Gai et al.
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From L. Lindegren
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AIM is devoted to the monitoring and diagnostics of the astrometric instrument response during in-flight operations.
It is an ensemble of software modules each one dedicated to perform a specific analysis and extract calibration information from the data during in-flight operation.
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AIM analysis 1: effects of perturbations
Instrument(physical
parameters)
Simulations
Simulated Data
Goal: identification of “critical parameters”
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AIM analysis 2: calibrate instrument model
Instrument(physical
parameters)
Simulations
Laboratory Data
Calibration procedure
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Gaia ASTRO Optical system data
FPA/CCD configurations
simulator module
Optical nominal and perturbed
configurations simulator module
Effective PSFs libraries
Gaia Astrometric Focal Plane Assembly
data
AIM - IM
Star spectral energydistribution (SED)
Catalogues Source constructor
module Polychromatic Effective PSF/LSFs libraries
Level 0
Optical PSFs libraries
GAIA raw elementary signal
Gaia Attittude data
Attitude simulator module
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AIM analysis 3: forward analysis
Instrument(physical
parameters)
Simulations
Simulated Data
Astrometric Instrument Model(effective global parameters)
?
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Instrument angular rate
WFE maps foreach SM/AF CCDShapingerrors mapfor each field
polishingerrors mapfor each field
Degradationreflectingsurface
mirrors position & orientation
no-uniformityAC FWCsensitivityvariationfringingaging
effectsinter-intra CCD vart.PRNUradiation
effects,CTI
OperationsOperations
Mirror CoatingTrasmissivityPolarization
effectsReflectivityStraylightOpticsOptics
Scanning law
AttitudeAttitude
NominalPerturbedPerturbed Nominal
CCD position & orientationGeometry
contributions
Geometrycontributions
saturationnonlinearityQE, MTF,gain, RONDetectorsDetectors
Perturbed Nominal
AIM - IM
Level 0-bis
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AIM analysis 4: backward analysis
Satellite Data
Calibration procedure
Astrometric Instrument Model(effective global parameters)
Instrument Monitoring
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BackwardAnalysis
BackwardAnalysisMerit statistics to
process raw data and performed data analysis (methods, algorithms)
Forward AnalysisForward Analysis
Telescope characterization analysis
CCD characterization analysis
Image characterization analysis
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Si individuano tre modelliI tre modelli sono collegati e in generale
dipendenti dal tempo Gerarchia:1) Risposta locale => forma della PSF/LSF effettiva2) Variazione distribuita sul campo => FPSM o varianti3) Legame campo-campo => base angle generalizzato
Sviluppo: analisi e identificazione parametri/forme funzionaliconvenienti; definizione algoritmi.Progresso documentato da pubblicazioni e note tecniche
Applicazioni: monitoraggio e analisi dati Gaia – identificazione di correlazioni, eventi critici, …
Modello di risposta strumentale per la riduzione dati di Gaia
Backward Analysis
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Risposta locale
Variazione distribuita sul campo
Legame campo-campo
CCD-Field transformationmodeling andestimation
CCD-Fieldtransformation
OperationsOperationsBase Angle
Forma della PSF/LSF policromatica effettiva
OpticsOptics
DetectorsDetectors
Geometrycontributions
Geometrycontributions
A)
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Gaia: Complete, Faint, Accurate
Hipparcos Gaia
Magnitude limit 12 20 mag Completeness 7.3 – 9.0 20 mag Bright limit 0 6 mag Number of objects 120 000 26 million to V = 15 250 million to V = 18 1000 million to V = 20 Effective distance limit
1 kpc 50 kpc Quasars None 5 x 105
Galaxies None 106 – 107 Accuracy 1 milliarcsec 7 µarcsec at V = 10 10-25 µarcsec at V = 15 300 µarcsec at V = 20 Photometry photometry
2-colour (B and V) Low-res. spectra to V = 20 Radial velocity None 15 km/s to V = 16-17 Observing programme
Pre-selected Complete and unbiased
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Payload and Telescope
Two SiC primary mirrors1.45 0.50 m2 at 106.5°
SiC toroidalstructure
(optical bench)
Basic anglemonitoring system
Combinedfocal plane
(CCDs)
Rotation axis (6 h)
Figure courtesy EADS-Astrium
Superposition of two Fields of View
(FoV)
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Focal Plane
Star motion in 10 s
Total field: - active area: 0.75 deg2
- CCDs: 14 + 62 + 14 + 12 - 4500 x 1966 pixels (TDI) - pixel size = 10 µm x 30 µm
= 59 mas x 177 mas
Astrometric Field CCDs
Blue Photometer CCDs
Sky Mapper CCDs
104.26cm
Red Photometer CCDs
Radial-Velocity Spectrometer
CCDs
Basic Angle
Monitor
Wave Front
Sensor
Basic Angle
Monitor
Wave Front
Sensor
Sky mapper: - detects all objects to 20 mag - rejects cosmic-ray events - FoV discriminationAstrometry: - total detection noise: ~6 e-
Photometry: - spectro-photometer - blue and red CCDsSpectroscopy: - high-resolution spectra - red CCDs
42
.35cm
Figure courtesy Alex Short
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In fase operativa le misure stesse saranno utilizzabili per estrarre l’informazione suiparametri strumentali. La media sulle diverse osservazioni sul transito ci permettera’ di raggiungere precisioni del μas sulla stima dei parametri. Basti pensare che gli oggetti piu’ brillanti di V=15 disponibili sono 40 milioni e il numero medio di oggettisimultaneamente osservati nei due campi di Gaia e’ dell’ordine di 1000.
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From L. Lindegren