During operation, telemetry containing STIS science data is downlinked through a
TDRSS satellite to a ground station in White Sands, NM. From there it is sent to Goddard Space Flight Center where the PACOR data capture facility collects the downlinked science data into telemetry “pod files”. These pod files are then transmitted to STScI where they are saved to a permanent storage medium. The STScI ingest pipeline then unpacks the data, extracts keywords from the telemetry stream, reformats the data, and repackages them into raw, uncalibrated, but scientifically interpretable data files. These raw files are then processed by the calstis
software to produce a variety of calibrated data files. The results of these procedures are then used to populate the databases that form the searchable archive catalog describing the individual instrument exposures. At this point, the raw and calibrated data files generated from the pod files are normally discarded. Only the pod files and the information placed in the archive databases are preserved.
Each time a user requests data from the Hubble Data Archive via the “On The Fly
Reprocessing” (OTFR) system, the raw files are regenerated from the original pod files, and then re-calibrated. What is described in this chapter is calstis
, the program that performs the calibration of STIS science data and is available to the community as part of the STSDAS
package. STIS data taken prior to the 2004 Side-2 electronics failure were recalibrated with the latest software available at the time as part of the STIS calibration closeout in 2006 (see Section 1.5
). See Section 3.6.1
for information on the updates made to calstis
since the STIS calibration closeout. The static STIS archive will make pre-SM4 raw and calibrated STIS data available without having to rerun OTFR and recreate all the files.
A more detailed description of the OTFR system as it applies to STIS and other HST
instruments can be found in Swade et al. (2001, ASP Conf. Ser., Vol. 238, 295), available on-line at:
is several pipelines in one, reflecting the complexity and diversity of STIS observing modes. Your STIS data will have been calibrated to different levels, depending on their nature:
See Chapter 2
for the naming conventions of the various input, intermediate, and output calibrated files.
As with the calibration pipelines for the other HST
instruments, the specific operations that are performed during calibrations are controlled by calibration switches
, which are stored in the image headers as KEYWORD=VALUE
pairs. Any given step in the calibration process may require the application of zero, one, or more calibration reference files
, the names of which are also found in the image header. The names of the keywords containing the switches and reference file names were introduced in the previous chapter; Section 3.3
will outline the role these keywords play in the data reduction, and description of the calibration steps are given in Section 3.4
. The path your data files take through the pipeline is determined by the calibration switches set in the primary header of the _raw data, which in turn depends directly on the type of data you have.
A few other general comments are in order. It is important to note that some of the
STIS calibration reference data are obtained contemporaneously with the science observations. These data may be used to refine the calibration process (as with the automatic wavecals), or may require you to replace a default calibration reference file with a contemporaneously obtained one, as in the case of a CCD near infrared (NIR) fringe flat. The details of how these contemporaneous calibration files are used in calstis
can be found in Section 3.4
. The STIS (and NICMOS) pipelines are also unusual in that they are re-entrant
. That is, a user running calstis
off-line may choose to reprocess STIS data partially, performing one or more of the intermediate steps without re-exercising the complete calstis
pipeline, for instance to perform cosmic ray rejection or one dimensional spectral extraction. Refer to Section 3.5
for the mechanics (and restrictions) of this kind of processing. Finally, as with other HST
propagates statistical errors and tracks data quality flags throughout the calibration process.