Space Telescope Science Institute
WFC3 Data Handbook 2.1 May 2011
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WFC3 Data Handbook > Chapter 3: WFC3 Data Calibration > 3.3 Keyword Usage

calwf3 processing is controlled by the values of keywords in the input image headers. Certain keywords, referred to as “calibration switches”, are used to control whether each available calibration step is performed or not. Another set of keywords, referred to as “reference file keywords”, indicate which reference files to use in the various calibration steps. The appropriate reference files are selected from the HST Calibration Data Base System (CDBS) during the OPUS Generic Conversion process. This is done by matching up certain instrument mode keywords, such as DETECTOR, CCDAMP, and FILTER, for the image being processed. The matching reference file names are then recorded in the reference file header keywords. The calibration switch and reference file keywords are listed in the flow charts shown in Figures 3.2, 3.3, and 3.4. Users who desire to perform custom reprocessing of their data may modify these keywords in the raw FITS file headers and then rerun the modified file through calwf3.
Occasionally there may be an instrument mode for which there is no calibration data. In these cases there will be a “placeholder” reference file in CDBS that is filled with zeros. Such reference files are identified by having their header keyword PEDIGREE set to “DUMMY”. When calwf3 encounters one of these reference files it will automatically skip the calibration step for which the file is used (e.g. DARKCORR will be skipped if the DARKFILE is dummy).
Other keyword values record instrument and detector parameters that are used in the calibration and some record information that is computed or derived during calibration. Table 3.3 provides a summary of the keywords used by calwf3, specifying whether they function as input or output to the task(s) listed in column 2. For a definition of each keyword see Tables 2.7, 2.8, and 2.9.
Table 3.3: WFC3 keywords used with calwf3.
Inverse sensitivity (ergcm-2-1DN-1)
calibrated read noise for amplifier A, B, C, and D (electrons)
Sample time of MULTIACCUM zeroth read (sec)
serious data quality flags considered ‘bad’ by calwf3
min, max and mean values of good pixels (electrons)
min, max, and mean signal to noise of good pixels
exposure start, and end times (modified Julian date)
number of image sets combined during CR rejection
rate at which pixels are affected by cosmic rays
Multiplicative term (in percent) for the noise model

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