Computer Science – Performance
Scientific paper
Oct 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007wfc..rept...22b&link_type=abstract
Instrument Science Report WFC3 2007-22
Computer Science
Performance
Hubble Space Telescope, Hst, Space Telescope Science Institute, Wide Field Camera 3, Wfc3, Thermal Vacuum Test, Uvis-2, Amp B Anomaly
Scientific paper
Thermal-vacuum (TV) level tests using the integrated WFC3 instrument were performed at Goddard Space Flight Center (GSFC) during the summer of 2007 with the designated flight-spare UVIS-2 detector in place. Routine data acquired during this TV revealed that amp B occasionally exhibited anomalous behavior. In particular, B-amp subarray readouts of point sources and flatfields at medium to high exposure levels showed smearing of the sources in the serial direction and pixels with count levels at precisely zero. Furthermore, in full-frame, four-amp readouts, with exposure levels near or beyond pixel saturation, quadrant B shows pixels with count levels dropping to zero although without any smearing effects. The issue was characterized further during TV and a potential fix identified: adjustment of the CCD last gate voltage. The fix has been validated with the UVIS-2 detector in WFC3 and was found to resolve the problem without apparent penalty, i.e., no adverse effect to amp A and no increase in readnoise. This report documents the characterization tests performed and the subsequent implementation and verification of the fix. Additional performance improvement may be achievable for extremely high exposure level images (>100x fullwell), by lowering the gate voltage 0.5-1 V for all amps; success in this case is not guaranteed, however, as the CCD output node threshold may be exceeded in these oversaturated images. Further test time would be required for confirmation.
Baggett Sylvia
Waczynski Augustyn
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