The New CALACS
Putting the electrons back where they belong
Linda Smith and the ACS+ Team
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New CALACS
• New version of CALACS will be released
in April
• Includes pixel-based CTE correction
• Corrections for all post-SM4 electronic
artifacts
• New data products
• New reference files
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CTE correction
• New CALACS uses a refined version of
the Anderson & Bedin (2010) code
• Includes time and temperature
dependence for CTE losses
• Improved correction at low levels
• Includes column-to-column correction
• Uses parallel processing
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Post-SM4 Artifacts
• Bias shift (banding at 0.02-0.3% of pixel
signal due to a mis-match in pre-amplifiers)
• Bias striping (due to electronic 1/f noise in
reference voltage)
• Cross talk between readout amplifiers
(present since installation)
• All of these are corrected in new CALACS
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ACS Observations of Saturn
Cross talk
Bias shift
Bias stripes
Uncorrected
Corrected
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Structure of new
CALACS
Raw Image
Bias-shift correction
Cross talk correction
All full frame
images
Bias-stripe correction
CTI correction
Dark correction using
standard DRK files
Data Products:
CRJ, FLT, DRZ
Standard CALACS
Dark correction using
new DKC files
Data Products:
CRC, FLC, DRC
CTE-corr CALACS
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New CALACS Files
3 pairs of products:
★_CRJ = Cosmic ray corrected FITS image
★_CRC = Cosmic ray and CTE-corrected FITS image
★_FLT = Flat-field corrected FITS image
★_FLC = Flat-field and CTE-corrected FITS image
★_DRZ = Drizzled FITS image
★_DRC = Drizzled CTE-corrected FITS image
Any data file with a type ending in “C” will be the CTEcorrected equivalent of a standard CALACS file
New reference files:
PCTETAB (CTE parameters)
DKC – CTE-corrected darks (1600)
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Current Status
• Code is finished
• Waiting for all DKC files to be delivered –
end of this week
• Start OPUS regression testing next week
• OPUS release expected in April
The ACS+ Team
J. Anderson, A. Armstrong, R. Avila, L. Bedin, M. Chiaberge, M. Davis, B.
Ferguson, A. Fruchter, D. Golimowski, S. Gonzaga, N. Grogin, W. Hack, P.
L. Lim, R. Lucas, A. Maybhate, M. McMaster, S. Ogaz, L. Smith, A. Suchkov,
L. Ubeda
Happy 10th
Birthday
ACS !!
SM3B ACS Installation 7 March 2002
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Review of Bias Shift
• The DSI-mode of the CEB-R induces a signal-dependent bias shift that ranges
from 0.02% to 0.30% among the four WFC quadrants.
• Two electronic components cause bias shift:
1. The AC filter (high pass filter) in the preamp.
2. The resistor mismatch in the dual slope integrator.
• The AC filter causes the DC offset of the preamp signal to vary with signal
intensity. If many bright/dark pixels are sampled consecutively, the average
DC offset rises/falls.
• The DC offset feeds the DSI, which integrates up for the reset (bias) level and
integrates down for the signal level. If offset is high/low, the DSI moves up and
down by a large/small amount. The mismatched resistors cause mismatched
gains in the up and down stages, and therefore a signal-dependent bias shift.
• Bias shift can be analytically removed using a parametric algorithm developed
by Markus Loose (ML), but parameters must be tuned for each quadrant.
5/28/2016