H. Bushouse
TIPS May 22, 2008
1
TV3 Science Team
Cast of “Characters”
• Instrument Scientists:
–Sylvia Baggett
–Howard Bond
–Tom Brown
–Howard Bushouse
–Susana Deustua
–Linda Dressel
–George Hartig
–Bob Hill (GSFC)
–Randy Kimble (GSFC)
–John MacKenty
–Andre’ Martel
–Peter McCullough
–Larry Petro
–Steven Rinehart (GSFC)
• QuickLook Operators:
–Elizabeth Barker
–Misty Cracraft
–Bryan Hilbert
–Sherrie Holfeltz
–Diane Karakla
–Jessica Kim
–Kevin Lindsay
–Doug Long
–Ray Lucas
–Jennifer Mack
–Helen McLaughlin
–Cheryl Pavlovsky
–Brittany Shaw
–Ed Smith
–Megan Sosey
–Alex Viana
• WFC3 Operations:
–Tom Wheeler
H. Bushouse
TIPS May 22, 2008
2
High-Level Statistics
• Total of 743 hours (31 days) on Science Calibration activities
– Initial ambient calibrations: Feb. 20 – 29
– Vacuum calibrations: Mar. 4 – Apr. 16
– Final ambient calibrations: Apr. 18 – 21
• 188 hours (8 days) spent on unplanned investigations
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UVIS window droplets
IR FPA persistence
IR bias jumps (“banding”)
UVIS PSF short-term stability (shutter-induced jitter)
UVIS electronic crosstalk linearity
• 555 hours (23 days) spent on original 20-day Science
Calibration plan activities (15% overrun)
• ~ 265 SMS runs; 10,605 exposures; ~25 lbs of M&M’s
H. Bushouse
TIPS May 22, 2008
3
Objectives Met
• Calibrate all WFC3 science modes
 Obtain all data necessary to support on-orbit science operations and data
calibration using UVIS-1’ and IR-4 detectors
 UVIS & IR detector calibrations: bias, dark, flat field, read noise, gain,
linearity, full-well, fringing, …
 System-level calibrations: system, filter, & grism throughputs
• Verify system-level performance
 Optical alignment, image quality, photometric stability, scattered light,
internal cal system performance
 Effects of input voltage and thermal cycling on calibrations
 Verify instrument performance model (Exposure Time Calculators)
• CEI spec and lien verifications, where possible
H. Bushouse
TIPS May 22, 2008
4
Accomplishments
• All tests in original 20-day calibration plan
accomplished
• No tests or calibrations deferred to SMOV
H. Bushouse
TIPS May 22, 2008
5
Sci Cal Tests Completed
Servicing Mission Aliveness/Functional Test
IR Photometric Stability
UVIS & IR Optical Alignment
IR Electronic Crosstalk
UVIS & IR Science Monitors
IR Bias/Dark vs. Orbit Cycling
IR Darks (read noise)
IR Rate Dependent QE
IR Background Levels vs. Filter
IR Intrapixel Sensitivity
IR FPA Gain
IR Persistence
IR FPA Linearity (full-well)
UVIS Bias (read noise)
IR Optical Performance (Encircled Energy)
UVIS Darks
IR Throughput
UVIS CCD Gain
IR Filter Blue Leaks
UVIS Linearity (full-well)
IR External & Internal Flat Fields
UVIS Optical Performance (Encircled Energy)
IR Flat Field Stability
UVIS System Throughput
IR Grism Narrowband Flat Fields
UVIS Filter Throughput
IR Grism Flux Calibration (throughput)
UVIS CCD Red Cutoff
IR Grism Dispersion & Spectral Trace
UVIS Filter Red Leaks
IR FPA Edge and Baffle Scattered Light
UVIS External & Internal Flat Fields
H. Bushouse
TIPS May 22, 2008
6
Sci Cal Tests Completed (2)
UVIS Flat Field Stability
UVIS Grism Narrowband Flat Fields
UVIS Grism Flux Calibration (throughput)
UVIS Grism Dispersion & Spectral Trace
UVIS CCD Fringing
UVIS Glint
UVIS Electronic Crosstalk
UVIS Filter Wedge
UVIS CTE EPER Flat Fields
Unplanned tests:
IR Bias Jump Monitor
UVIS Window Droplet Investigations
UVIS PSF Stability (shutter-induced jitter)
UV Quantum Yield Measurements
UVIS CCD Amplifier “smearing” check
H. Bushouse
TIPS May 22, 2008
7
UVIS CCD Characteristics
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Read noise: 3.0–3.3 e- rms
Dark current: <1 e-/pix/hour
Full-well: 70-85k eAll consistent with TV1 results using detector
with same CCD chips
H. Bushouse
TIPS May 22, 2008
8
UVIS Flat Fields
15% structure
F814W
F275W
F555W
59 of 66 filters have total of 120ke- in flats (0.3%)
7 (all narrow quads) have 40-80ke- (0.4-0.5%)
H. Bushouse
TIPS May 22, 2008
7% structure
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IR FPA Characteristics
• Read noise in a CDS difference image: ~22 e-/pix rms
– Averages down to ~14 e- over 16 samples
Dark current: ~0.05 e-/pix/sec
• Linearity: 5% at ~72k e– Hard saturation at ~84k eH. Bushouse
TIPS May 22, 2008
10
IR Flat Fields
>200k e- in all
IR flats (~0.2%)
“Death Star”
H. Bushouse
TIPS May 22, 2008
“Wagon Wheel”
35-40% structure
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Orbital Cycling
• Vary thermal environment and WFC3 input voltage to
simulate orbital cycles
• Check IR FPA
temperature and
bias stability
Temp stable to ~0.6 K
H. Bushouse
TIPS May 22, 2008
12
Open Issues/Studies
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UVIS “bowtie” feature
UVIS shutter-induced image jitter
IR image persistence
Launch on Side 1 or 2?
– Intermittent IR bias jumps seen on Side 1
– UVIS shutter jitter somewhat worse on Side 2
H. Bushouse
TIPS May 22, 2008
13
UVIS “Bowtie”
• Regions of enhanced
brightness
occasionally seen in
darks and flats
• Example here is at
strongest level yet
seen (5% UV flatfield
enhancement in the
bowtie and in the
location of two
alignment spots)
• Typical levels are
much less (0.5-1%)
H. Bushouse
TIPS May 22, 2008
14
Bowtie Investigation
• Physical mechanism not understood; there appears to be both a persistence
and a QE hysteresis phenomenon at work
• Physical morphology is suggestive of a charging effect (electrical field
“pincushion” morphology)
• The DCL has never seen this behavior in testing of e2v devices, yet it has
been seen with UVIS-1, UVIS-2, and UVIS-1’ in WFC3
• Science team is surveying all biases, darks, and flats from T/V-1, TV-2, and
TV-3 to identify all examples and search for trends, correlations
• Seems to occur most often in images taken in ambient (CCD’s warmer than
flight), or soon after detector cooldown, but not always
• The clear CCD-level symmetry naturally suggests a CCD-level cause – no
upstream sources (optics, stray light, CASTLE illumination) know anything
about the split focal plane
• The problem does not arise in the readout electronics (not present in the
overscan; readout wouldn’t know about alignment spots)
H. Bushouse
TIPS May 22, 2008
15
UVIS Shutter-Induced Image Jitter
• Series of short (1 sec)
exposures shows lower peak
pixel fraction and larger PSF
width in alternating images,
while total flux is constant
• Phase of alternating behavior
correlates with phase of the
2-blade shutter mechanism
• For exposures >5-10s, no
significant effects are seen
H. Bushouse
TIPS May 22, 2008
16
Effects Are Strongest In Short
Exposures and Small Apertures
• Theory: motion of shutter
induces mechanical jitter in the
instrument that slightly blurs
short exposures; the element
most likely affected is the
UVM1 mirror (<1 arcsec of
rotation of that optic is
required to produce the effects
observed)
• Possible changes to shutter
operations (starting position,
encoder feedback, etc) under
investigation
H. Bushouse
TIPS May 22, 2008
EE (diameter in arcsec)
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IR Image Persistence
• Initial test using 0.5x-100x full-well sources showed negative persistence
(essentially negative dark current); never seen in DCL tests
• Severe over-illumination had occurred due to ground test equipment
• Reran with modified techniques, which showed normal positive persistence,
and was (as expected) very low for the sub-full-well exposures
• Target brightness constraint for IR channel could result, though the strong
preference is to avoid this; perhaps at least an alert to observers as to the
potential effects of very bright objects in their target fields
H. Bushouse
TIPS May 22, 2008
18
IR Bias Jumps:
Gone but not forgotten
• Low-level bias shift
(~2.5DN) was seen
intermittently only in lower
left quadrant of readout;
effect is tracked by the
reference pixels in those rows
• Only seen with Side 1
electronics
• Initial rate of occurrence:
~4.5% of all reads
• After March 19: zero in
>3000 reads
H. Bushouse
TIPS May 22, 2008
19
Results & Remaining Work
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ISR 2008-05 “IR Channel Blue Leaks”, T. Brown
ISR 2008-06 “IR Channel Baffle Scatter”, T. Brown
ISR 2008-07 “UVIS Channel Glints”, T. Brown
ISR 2008-08 “UVIS Filtered Throughput”, T. Brown
ISR 2008-09 “IR Channel Throughput”, T. Brown
 Finish TV3 analysis and delivery of calibration reference
files by end of July
H. Bushouse
TIPS May 22, 2008
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