Corot Instrument Characterization based on in-flight collected data
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Corot-Brazil Workshop – October 31, 2004 1Leonardo Pinheiro da Silva
Corot Instrument Characterizationbased on in-flight collected data
Leonardo Pinheiro da Silva
Corot-Brazil Workshop
October 31, 2004
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Corot-Brazil Workshop – October 31, 2004 2Leonardo Pinheiro da Silva
Introduction
• Some instrument components are susceptible to physical phenomena leading to undesired effects on the scientific data
• some might be corrected through modeling, with basis on correlated collected data (e.g. HK data)
• others are expected to be negligible, given the defined specifications for the photometric signal
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Corot-Brazil Workshop – October 31, 2004 3Leonardo Pinheiro da Silva
Objectives
• Though the analysis and characterization of some critical aspects we intend to:
• validate the theoretical models to be used on ground-based corrections
• evaluate the respective modeling parameters• verify the hypothesis enabling some of the noise
sources to be neglected
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instrument optics
CCD detectors
readout electronics
Some Aspects of Interest
- PSF (Temp. of the Lenses)
- Bias Level (Temp. of Analogic Comp.)
- Electronics’ Gain (Aging)
- Spontaneous Generation of e- (CCD Temp.)
- Pixel Response Non-Uniformity (+Attitude Jitter)
- p+ Impacts (Geo. Position, Effective Shielding)
...
digital processing
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Corot-Brazil Workshop – October 31, 2004 5Leonardo Pinheiro da Silva
• Reduction of in-flight calibration data to provide:
• Dark Fields• Bright pixels map• Dark current law as f(T)
• Flat Fields• Black pixels map• Local PRNU statistics
I. CCDs: Classic Characterization
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• CCDs are susceptible to radiation which depends:• on the satellite position in orbit• on the effective shielding
• Effect on the photometry will depend on:• the energy of incoming impacts (generated e-)• the impacted area of the CCD (disturbed pixels)
• Specific tools to characterize:• incoming impacts as a function of satellite coordinates• impact effects on the CCD (energy and scale statistics)
CCDs: p+ Flux at the Focal Plane
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Corot-Brazil Workshop – October 31, 2004 7Leonardo Pinheiro da Silva
(…)
(…)
• Set of images + satellite orbit data => p+ flux (lat, lon) [p+/cm2/s]
CCDs: p+ Flux at the Focal Plane
(lat,lon)
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II. Optics: Spread Function
• Collected star light is spread over a region of the detector’s surface• distribution profile depends on stellar magnitude and
type, position in the field of view, lenses’ temperature, ..
• Knowledge about the spread function is useful in jitter corrections and star coordinates evaluation
• Specific tools to estimate:• high-resolution (sub-pixel) spread functions, given a set
of images and corresponding satellite attitude data
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Spread Function: Sampled Dataac
quire
d d
ata
proj
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splin
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Spread Function: Data Acquisition
(m=6; T=6000K) restituted image
?attitude
jitterspatial
sampling
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Spread Function: Restitutionty
pic
al s
ampl
epr
ojec
ted
imag
ere
stitu
ted
imag
e
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III. Readout Electronics
• Signal conditioning is done between the CCD outputs and A/D conversion• Signal is amplified, an offset is imposed
• Components are sensitive to thermal fluctuations and aging
• Specific tools to characterize the behavior of:• the offset level• the electronic gain• the readout noise
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Ast
ero
1L
Exo 1
LExo 2
LA
stero
2L
• Correlation to T probes, thermal sensitivity, temporal evolution, spectra, ..
Example: Electronic Bias
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Conclusion
• Data processing algorithms have been developed with basis on available in-flight data and calibration requirements
• The set of algorithms has been integrated in a mock-up and will soon be migrated to an operational structure
• Further work is to be done on other instrument aspects which might also be interesting to characterize...