Discussion of CalWebb contents

M. Robberto (facilitator)

MASKCORRBad Pixel Mask

*_RAW.fitsData cube file

DQ*_MSK.fitsMask file

REFCORRRef.pixel correction

ERR/REFRef. method flag

BDCORRBias/dark correction

ERR*_DRK.fits

Dark cube file

LINCORRLinearity correction

ERR*_LIN.fitsLinearity table ITIME

SAMP

_IMA out?*_IMA.fits

Data cube file

CRWFCORRCosmic/Weight/Fit

*_NOI.fitsReadout noise file

ERR

*_CRT.fitsCount rate file

File in Procedure File outModified Non-SCI

Extensions

CALWebb

MASKCORR

Flag values from the static bad pixel mask file are added to the DQ image.

1. How many types of bad pixels do we expect?hot, cold, dead, unstable, low QE, early saturation…

2. Can the user select the types of bad pixels to reject?

3. How do find bad pixels?dark => hotflat field => colddifference => dead…

4. Bad Reference pixels

REFCORR

Reference pixels track voltage and allow to correct for time dependent drifts of the signal offset.

Both the Rockwell H2RG arrays and the MIRI IBC arrayscontain reference pixels. MIRI also contains additionalreference outputs.

1. Are all reference pixels equally good? (not the case in WFC3)

2. How do we extract the reference value?

3. What do we do with the reference value?

4. Temperature effects?

5. Are reference pixels really insensitive to light?

6. What do we do with subarrays?

BDCORR (Bias and Dark subtraction)

The BDCORR step subtracts the dark reference images, readout-by-readout for MULTIACCUM observations, from the science data.

STScI will maintain a library of dark current images (files *_DRK.fits) for all instruments, covering the entire range of predefined MULTIACCUM sample sequences.

1. Are bias and dark stable? Do we need to perform extra correction (e.g T dependent darks)?

2. Should we take darks for all readout modes? What about subarrays?

3. If there is a light leak, do we need filter dependent “darks”? Should we anticipate these cases?

4. How do we account for the dark current noise?

LINCORR (Linearity correction)

The LINCORR step applies the linearity correction to pixels with signal below their defined saturation levels. However, it applies no correction to pixels in the high signal regime, but rather flags them as saturated in the DQ image.

1. How do we really estimate the linearity correction?

2. Are (all) pixels linear at low fluxes? Should we distinguish between non linearity and reset anomaly? How?

3. Is it wavelength dependent? Does it depend on the photon rate?

4. How do we estimate the noise on the linearity correction?

CRID-WEIGHT-SLOPEFIT (Produce Slope Images)

CRID: identify and flag pixels suspected of containing cosmic ray (CR) hits,

WEIGHT: apply the proper weight to the single reads

SLOPEFIT: combine the data from all readouts into a single image.

(M. Regan)