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

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

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

Corot-Brazil Workshop – October 31, 2004 4Leonardo Pinheiro da Silva

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

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

Corot-Brazil Workshop – October 31, 2004 6Leonardo Pinheiro da Silva

• 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

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)

Corot-Brazil Workshop – October 31, 2004 8Leonardo Pinheiro da Silva

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

Corot-Brazil Workshop – October 31, 2004 9Leonardo Pinheiro da Silva

Spread Function: Sampled Dataac

quire

d d

ata

proj

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d im

age

splin

e in

terp

ola

tion

Corot-Brazil Workshop – October 31, 2004 10Leonardo Pinheiro da Silva

Spread Function: Data Acquisition

(m=6; T=6000K) restituted image

?attitude

jitterspatial

sampling

Corot-Brazil Workshop – October 31, 2004 11Leonardo Pinheiro da Silva

Spread Function: Restitutionty

pic

al s

ampl

epr

ojec

ted

imag

ere

stitu

ted

imag

e

Corot-Brazil Workshop – October 31, 2004 12Leonardo Pinheiro da Silva

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

Corot-Brazil Workshop – October 31, 2004 13Leonardo Pinheiro da Silva

Ast

ero

1L

Exo 1

LExo 2

LA

stero

2L

• Correlation to T probes, thermal sensitivity, temporal evolution, spectra, ..

Example: Electronic Bias

Corot-Brazil Workshop – October 31, 2004 14Leonardo Pinheiro da Silva

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...