The initial input files to the calibration program calwf3
are the raw files (raw) from Generic Conversion and the association (asn) table, if applicable, for the complete observation set.
The final output files will be renamed with the "_flt" or "_flc" suffixes after the standard calibrations (flat fielding, dark subtraction, etc.) are complete. The "_blv_tmp" files serve as input for cosmic ray rejection, if required. For UVIS CR-SPLIT
exposures, a temporary CR-combined image is created and then renamed with either the "_crj" or "_crc" suffix once basic calibrations of that image are complete. With the addition of the CTE correction, which is the very first step, the pipeline now follows two distinct lines of processing, one with the CTE correction applied and one without. Users running raw data through calwf3
which has PCTECORR set to PERFORM should expect to see both sets of calibrated files when the tasks are complete.
The final products of the calwf3 pipeline are not corrected for geometric distortion. AstroDrizzle
is used to correct all WFC3 images for geometric distortion, whether they are taken as single exposures or as part of an association. Astrodrizzle
is distributed as part of the
package, used for aligning and combining all HST images. For CR-SPLIT
supersedes the calwf3
cosmic-ray rejection processing and uses the individual "_flt" or "_flc" files directly as input, performing cosmic-ray rejection in the process of producing the final drizzled image from multiple exposures (see
). This has significant advantages in cases where small numbers of CR-SPLIT
images were obtained at a small number of different dither positions, because AstroDrizzle will use all the information from all the input files to produce the best cosmic-ray rejection. The resulting drizzled images should generally be useful for science, although subsequent reprocessing off-line may be desirable in some cases to optimize the data for specific scientific applications.
Association tables are useful for keeping track of the complex set of relationships that can exist between exposures taken with both WFC3 channels, especially with REPEAT-OBS
, and dithered exposures. Images taken at a given dither position may be additionally CR-SPLIT
into multiple exposures (e.g., UVIS observations). In these cases, associations are built to describe how each exposure relates to the desired final product. As a result, WFC3 association tables can be used to create one or more science products from the input exposures. The relationships defined in the association tables determine how far through the calibration pipeline the exposures are processed and when the calibrated exposures get combined into sub-products for further calibration.
A sample association table for a two-position dithered observation with CR-SPLIT=2
is presented in
This example shows how both MEMNAME
are used to associate input and output products. The MEMTYPE
for each component of the first CR-SPLIT
exposure, IxxxxxECQ and IxxxxxEGQ, are given the type EXP-CR1
. The sub-product Ixxxxx011 is designated in the table with a MEMTYPE
. The last digit of the product filename corresponds to the output product number in the MEMTYPE
. A designation of zero for the last digit in the filename is reserved for the dither-combined product.
The column MEMPRSNT
indicates whether a given file already exists. For example, if cosmic ray rejection has not yet been performed by calwf3
, the PROD-CRn
files will have a MEMPRSNT
value of "no". The sample association table in
shows the values of MEMPRSNT
prior to calwf3 processing.
In order to create a geometrically correct, drizzle-combined product, PROD-DTH
exposures are combined only with Astrodrizzle
, which executes after calwf3
has finished processing all members. PROD-RPT
products are combined using
and all output files have the “cr” extension.
Each task used by calwf3
creates messages during processing that describe the progress of the calibration and are sent to STDOUT. In calibration pipelines written for other HST instruments, trailer files were created by simply redirecting the STDOUT to a file. Because multiple output files can be produced in a single run of calwf3
, creating trailer files presents a unique challenge. Each task within calwf3
must decide which trailer file should be appended with comments and automatically open, populate, and close each trailer file.
will always overwrite information in trailer files from previous runs of calwf3
while preserving any comments generated by Generic Conversion. This ensures that the trailer files accurately reflect the most recent processing performed. The string "CALWF3BEG
" will mark the first comment added to the trailer file. If a trailer file already exists, calwf3
will search for this string to determine where to append processing comments. If it is not found, the string will be written at the end of the file and all comments will follow. Thus any comments from previous processing are overwritten and only the most current calibrations are recorded.
As each image is processed, an accompanying trailer file with the "*_trl.fits" suffix will be created. Further processing with calwf3
will concatenate all trailer files associated with an output product into a single file. Additional messages will then be appended to this concatenated file. This duplicates some information across multiple trailer files but ensures that for any product processed within the pipeline, the trailer file will contain processing comments from all the input files.
Linking trailer files together can result in multiple occurrences of the "CALWF3BEG
" string. Only the first, however, determines where calwf3
will begin overwriting comments if an observation is reprocessed.