Instrument Monitoring


Anneal History

A complete history of all on-orbit WFC3/UVIS detector anneals is provided. The anneal procedures, performed monthly, warm the detectors to +20°C and restore 20-30% of the hot pixels to their original levels.

Complete Anneal History


Throughout the lifetime of WFC3, a growing number of ‘blobs’ (small, circular regions with slightly decreased sensitivity) have appeared in WFC3/IR images. The blob monitor allows us to identify and flag new IR blobs that appear and monitor the repeatability of the Channel Select Mechanism (CSM) movements.

The accumulation of blobs on the IR sensor over time

ISR 2018-06: WFC3/IR Blob Monitoring 
B. Sunnquist 08 May 2019 (last updated)


The UVIS detector occasionally exhibits low-level (~1%) quantum efficiency offsets (i.e. hysteresis) across both chips. This hysteresis has been dubbed the 'bowtie' effect, due to the unique pattern that results in the image ratios. Ground tests found that by overexposing the detector to several times the full well amount, this hysteresis could be negated. The results of the 'bowtie monitoring' program are provided here.

Median flatfield (image3/image3) ratio levels as a function of day since June 11th, 2009


ISR 2014-13: No Evidence Found for WFC3/UVIS QE ‘Overshoot’
M. Bourque, S. Baggett, & L. Dressel 29 May 2014 

ISR 2013-09: WFC3/UVIS Bowtie Monitor
M. Bourque and S. Baggett 25 Jun 2013

ISR 2009-24: WFC3 SMOV Proposal 11808: UVIS Bowtie Monitor.
Baggett and Borders 26 Jan 2010 


HST spectrophotometric standards are routinely observed to monitor throughput stability. Analysis of the high signal-to-noise photometry in W and M bands indicates that the instrument is photometrically stable, with measured variations that are <0.4%. The measure of the photometric throughput of WFC3 as a function of time also checks for the presence of possible contaminants on the optics.


ISR 2018-16: WFC3/UVIS - Temporal and Spatial Variations in Photometry
H. Khandrika, S. Deustua, J. Mack 08 Nov 2018

ISR 2017-15: 2017 Update on the WFC3/UVIS Stability and Contamination Monitor
C. E. Shanahan, C. M. Gosmeyer, S. Baggett 12 June 2017

ISR 2014-20: Update on the WFC3/UVIS Stability and Contamination Monitor
C.M. Gosmeyer, S. Baggett, S. Deustua, & D.M. Hammer10 Sep 2014 

ISR 2010-14:The Photometric Performance of WFC3/UVIS:Temporal Stability Through Year 1.
Kalirai et al. 14 Oct 2010 


Charge Transfer Efficiency/Extended Pixel Edge Response

For information on how CTE losses affect science data as well as options for mitigating those losses, please see CTE Information

The EPER (Extended Pixel Edge Response) method can be used to measure CCD detector Charge Transfer Inefficiency (CTI)-induced losses via internal exposures. EPER data consist of short tungsten lamp flat field exposures in several filters in order to obtain a large range of illumination levels (from ~100e- to 4000e-). By measuring the signal profiles as they extend into the trailing overscan region, an assessment can be made of the CTE level. Please see the most recent report for current plots.

Tabulated data of EPER CTE levels as a function of signal and time
Columns are filename (date encoded as ddmmyy), Modified Juilan Date, average signal across all four amps at five different levels (cols 3-7), CTE for those average signals (cols 8-12), and the error bars for the EPER CTE measurements (cols 13-17).

CTE-EPER vs. Time Plot


ISR 2016-10: WFC3/UVIS EPER CTE Cycles Aug 2009 - Apr 2016 
H. Khandrika, S. Baggett, A. Bowers 23 May 2016

ISR 2013-03: WFC3/UVIS EPER CTE Measurement: Cycles 19 & 20
M. Bourque & V. Kozhurina-Platais 15 Feb 2013 

ISR 2011-17: WFC3/UVIS CTE-EPER Measurement: Cycle 17 & 18. 
Khozurina-Platais et al. 27 Sept 2011 

2010 HST Calibration Workshop Proceedings: Internal Monitoring of WFC3/UVIS Charge Transfer Efficiency.(see page 573)
Khozurina-Platais et al. 2010 

ISR 2009-10: WFC3/UVIS CTE-EPER Measurement. 
Khozurina-Platais et al. 21 Jun 2009 

ISR 2007-13: UVIS CCD EPER CTE measurements performed during the April 2007 Ambient Calibration campaign (SMS UV02S01). 
M. Robberto 2007


The WFC3 dark current slowly increases over time and is monitored each cycle. This monitoring enables the creation of superdark reference files for the calibration pipeline and the monitoring of dark current and hot pixels. 

UVIS Hot Pixels

Hot Pixel Evolution Chip 2 UVIS
WFC3/UVIS (Chip 2, Amps C & D)
This plot shows the hot pixel growth between anneals for WFC3/UVIS. The number of hot pixels are plotted as a function of time since the installation of WFC3 on HST, where red lines represent SIC&DH failures, when WFC3 was safed, and the grey/white regions represent anneal cycles. Note that the implementation of post-flash occurred on day 1246.


Dark Current

Dark Current UVIS Chip 2
WFC3/UVIS (Chip 2, Amps C & D)
Shows the dark current vs. time for WFC3/UVIS. The red lines represent SIC&DH failures, when WFC3 was safed, and the grey/white regions represent anneal cycles. Note that the implementation of post-flash occurred on day 1246.



ISR 2016-08: WFC3/UVIS Dark Calibration: Monitoring Results and Improvements to Dark Reference Files
M. Bourque and S. Baggett 22 April 2016 

ISR 2014-04: WFC3 Cycle 19 & 20 Dark Calibration: Part I
J. Biretta and M. Bourque 10 April 2014 

ISR 2009-16: WFC3 SMOV Proposals 11419, 11426, 11431, and 11446: On-Orbit Darks.
Borders and Baggett 16 Nov 2009 


Gain is the conversion factor from electronic analog digital units (ADUs) to electrons, and is a fundamental parameter needed to characterize the WFC3 IR and UVIS detectors. In order to ensure that the true value of the gain in each quadrant does not deviate significantly from the nominal gain it is monitored each cycle.

Cycle 25 Gain Plot

Cycle 25 Gain Plot UVIS
Cy 25 mean-variance plot for Quad A, B, C, and D (UVIS)
IR Gain
IR Gain over time

SMOV Gain Plot
SMOV mean-variance plot for Quad A, B, C, and D.

TV3 Gain Plot
TV3 mean-variance plot for Quad A, B, C, and D.


ISR 2017-08: Monitoring the WFC3/UVIS Relative Gain with Internal Flatfields
J. Fowler & S. Baggett 15 March 2017

ISR 2013-02: WFC3 Cycle 19 Proposal 12690: UVIS Gain
H. Gunning, C. Pavlovsky, S. Baggett 29 Jan 2013

ISR 2011-13: WFC3 Cycle 17 Proposal 11906: UVIS Gain
Borders, Pavlovsky, and Baggett 23 June 2011

LAST UPDATED: 06/17/2019

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