Calibration and
Data Reduction
The pipeline processing of WFPC2 data sets reformats the telemetry received from HST into group FITS format images, generates headers containing a large number of keywords taken from both the HST and WFPC2 telemetry streams, in addition to various STScI ground system databases, and applies the calibration described below. This calibration is done with a module known as "CALWP2" which is written in the IRAF SPP language and is available, in identical form, to users of the STSDAS system. Therefore, off-line recalibration of observations is fairly easy, and will use the same program as the PODPS system. Documentation is available in the HST Data Handbook, and the STSDAS User's Guide.
CALWP2 performs the following operations if required by the observation:
- ADC correction
- Bias level removal
- Bias image subtraction (depending on the gain channel in use)
- Dark image scaling and subtraction
- Shutter shading correction
- Flat field image correction
- Population of various photometric calibration keywords
In addition, the following conditions are flagged in the Data Quality File (DQF):
- Transmission failures and other possible failures
- Known bad pixels (e.g. blocked columns)
- Pixels at or above the maximum A/D converter level (i.e. saturated)
- Bad pixels in reference images