WFC3 Data Handbook V. 4.0

help@stsci.edu

3.6	When should I recalibrate my data?

The goal of the STScI WFC3 pipeline is to provide data calibrated to a level suitable for initial evaluation and analysis for all users. When data sets are retrieved from the Hubble Data Archive (HDA) they are always reprocessed from scratch using the latest available calibration reference files and software updates. At times, however, observers may require a detailed understanding of the calibrations and processing applied to their data and the ability to repeat, often with improved products or non-default processing options, the calibration process at their home institution. There are several occasions when the data obtained from the HDA may not be ideal and when off-line interactive processing by the user is required:

•	when running calwf3 with personal versions of reference files or when using new reference files downloaded from the WFC3 website not yet available in the pipeline,

•	when running calwf3 with non-default calibration parameter values,

•	when images must be cleaned of artifacts such as new hot pixels or cosmic-rays that are not properly cleaned with automatic processing.

While the final drizzled images from AstroDrizzle are produced using parameters that are suitable for a wide range of scientific applications, there are often times when specific datasets would benefit significantly from further customized processing off-line. For example, a different output pixel scale or image orientation may be desired, image offsets may need to be refined, or cosmic-ray rejection parameters might need to be slightly adjusted. The same versions of calwf3 and AstroDrizzle that are used in the STScI pipeline are therefore also available to users in STSDAS and PyRAF. AstroDrizzle provides a single-step interface to the complex suite of tasks in the stsci_python drizzlepac package (See the drizzlepac website for more information.) It may be imported into any python or PyRAF environment but is not dependent on PyRAF or IRAF.

Reprocessing data to use alternate reference files, however, must be done at the user’s home institution. For example, there may be times when a user finds the need to use a custom bad pixel table to handle spurious conditions in their datasets that aren’t covered by the standard bad pixel table used in the STScI pipeline. On these types of occasions users can rerun their datasets through calwf3 or AstroDrizzle using their own customized reference data. Examples of how to do this are discussed below.