micro-arcsec mission:

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

7 maggio 2009 Busonero - 53° Congresso SAIt - Pisa 2

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



Astrometric solution for Gaia: Formulation

From L. Lindegren


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


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.


From B. Holl


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



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 .


Cromatic displacement for Astro 1


Cromatic displacement for Astro 2


Field distortion (due to optics)

See also D.Busonero et al. A&A 2006


Field distortion (due to CTIs)


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


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)



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.


From L. Lindegren


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.


AIM analysis 1: effects of perturbations

Instrument(physical

parameters)

Simulations

Simulated Data

Goal: identification of “critical parameters”


AIM analysis 2: calibrate instrument model

Instrument(physical

parameters)

Simulations

Laboratory Data

Calibration procedure


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


AIM analysis 3: forward analysis

Instrument(physical

parameters)

Simulations

Simulated Data

Astrometric Instrument Model(effective global parameters)

?


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


AIM analysis 4: backward analysis

Satellite Data

Calibration procedure

Astrometric Instrument Model(effective global parameters)

Instrument Monitoring


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


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


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



A)


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


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)


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


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.


From L. Lindegren

micro-arcsec mission:

Documents

congresso sait pisa7

congresso sait pisapre

astrometric parameters

instrument response

astrometric response

instrument monitoring

instrument diagnostic

litegaia7 maggio