Computer Science
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007wfc..rept...15b&link_type=abstract
Instrument Science Report WFC3 2007-15, 6 pages
Computer Science
Hubble Space Telescope, Hst, Space Telescope Science Institute, Wide Field Camera 3, Wfc3, Uvis Readnoise
Scientific paper
The WFC3 UVIS readnoise levels have been measured using recent ambient-level data obtained with the integrated instrument in the Space Systems Development and Integration Facility (SSDIF) clean room at Goddard Space Flight Center (GSFC). The UVIS-2 detector was in place, operating at -54C. Under these conditions, the readnoise levels in full-frame, four-amp bias image readouts, using a gain level of 1.5 e-/DN, are 3.1, 3.2, 2.8, and 3.1 e- for amps A,B,C, and D, respectively; errors are <0.1 e-. Application of the measured UVIS-2 gain values will increase the values by 3-10%, depending upon the specific amp. The readnoise has been measured in bias frames using the overscan region and the science area pixels; both methods yield effectively the same result. The overscan method has also been applied to non-bias images; the resulting readnoise levels differed from the bias frame results by 1-6% (0.02 to 0.2 e-), usually higher in the non-bias frames but not always. The readnoise in subarray images has also been evaluated; in 200x200 pixel subarray biases, the levels are slightly lower in amps A,B, and D (by ~0.02-0.15 e-) and slightly higher in amp C (~0.04e-) compared to the full-frame biases. Finally, an ambient superbias has been constructed from a stack of all good, full-frame, four-amp bias frames and its characteristics are described. There is some low-level systematic behavior to the noise in quadrant B: the bias level is slightly higher in odd-numbered columns than in even-numbered columns (~0.2 e- peak to peak). If this characteristic persists in images taken during the upcoming thermal vacuum tests and is found to vary with time, the pipeline algorithms could be modified to provide a column-dependent overscan correction.
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