FOC Data Analysis
and Products
Pipeline Processing
All data taken by the FOC are automatically processed and calibrated by the Routine Science Data Processing (RSDP), also called the "pipeline". It is possible to repeat, off line, the calibration part of the pipeline processing by using an IRAF/STSDAS task called calfoc (CALibration of FOC data), used automatically by the pipeline.
For every observation, the user will receive two sets of data coming out of the pipeline: the input and output files to calfoc. The input files to calfoc are:
- The raw image,.
- A mask image characterizing the location of known bad pixels, reseaux, and likely data errors determined by on-line processing of transmitted data called the Data Quality File.
- A file containing astronomical information related to the observation called the Standard Header Packet.
- A file containing engineering data related to the observation called the Unique Data Log.
The output files from calfoc are:
- The geometrically corrected image.
- The geometrically and photometrically corrected image.
- A trailer file (*.trl) containing a log of the pipeline processing.
The data processing flow chart for normal imaging and spectrographic images is shown in Figure blah. calfoc assumes that the processing parameters are in the image header, either directly from RSDP preprocessing, or inserted by task cloadrsdpx or loadrsdpx. The processing parameters govern which correction steps are to be performed, and which calibration files are to be used. For normal imaging observations, the following steps are performed in order:
- Dark count subtraction (not done at this time).
- Format dependent photometric correction (using ITF reference file) (not done at this time).
- Unzoom the zoomed image.
- Absolute calibration affecting header parameters only.
- Geometric distortion correction involving data interpolation and requiring a new mask image.
- Relative calibration or flat field correction (removing instrumental sensitivity variations) using UNI reference file, which is a reciprocal of a flat field.
For spectrographic (long-slit) observations, the final step is different i.e.:
- Spectrographic relative and absolute calibrations with flux and wavelength calibrations affecting both data and headers.
In the spectrographic mode, several orders may overlap. The pipeline does not deliver separately calibrated data sets for each order, leaving line identification and order deconvolution to the user. The pipeline delivers the raw image and data sets corresponding to the results of the tasks as indicated in Figure 10.1. Detailed information on FOC calibration procedures and algorithms can be found in the "Requirements Section" of the "Design Manual, DRD-SOGS-SE-06-1," available from STScI. Some more general information is contained in the Calibration HST Data Set manual. See also the STSDAS Calibration Guide.
- Figure 10.1: - Flow Diagram of FOC Imaging Data through Routine Science Data Processing System.
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