The suffixes used for WFC3 raw and calibrated data products are described in
the following and closely mimic those used by ACS and NICMOS.
Association Tables
Association tables are useful for keeping track of the complex set of
relationships that can exist between exposures taken with WFC3, especially
with REPEAT-OBS, CR-SPLIT, and dithered exposures, for both the UVIS and
IR channels. 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,
just like ACS associations. 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.
The format of WFC3 association tables closely resembles the ACS and
NICMOS association format, with three primary columns: MEMNAME, MEMTYPE,
and MEMPRSNT. The column MEMNAME gives the name of each exposure making up
the association and output product name(s). The column MEMTYPE specifies
the role that the file has in the association. WFC3 uses the same set
of MEMTYPES as ACS to provide support for multiple products.
Exposure types in WFC3 associations. The suffix "n" is appended to the MEMTYPE when multiple sets are present within a single association.
| MEMTYPE | Description |
|---|
| EXP-CRJ | Input CR-SPLIT exposure (single set) |
| EXP-CRn | Input CR-SPLIT exposure for CR-combined image n (multiple sets) |
| PROD-CRJ | CR-combined output product (single set) |
| PROD-CRn | CR-combined output product n (multiple sets) |
| EXP-RPT | Input REPEAT-OBS exposure (single set) |
| EXP-RPn | Input REPEAT-OBS exposure for repeated image n (multiple sets) |
| PROD-RPT | REPEAT-OBS combined output product (single set) |
| PROD-RPn | REPEAT-OBS combined output product n (multiple sets) |
| EXP-DTH | Input dither exposure |
| PROD-DTH | Dither-combined output product |
Sample Association Table Ixxxxx010_ASN
| MEMNAME | MEMTYPE | MEMPRSNT |
|---|
| IxxxxxECQ | EXP-CR1 | yes |
| IxxxxxEGQ | EXP-CR1 | yes |
| Ixxxxx011 | PROD-CR1 | no |
| IxxxxxEMQ | EXP-CR2 | yes |
| IxxxxxEOQ | EXP-CR2 | yes |
| Ixxxxx012 | PROD-CR2 | no |
| Ixxxxx010 | PROD-DTH | no |
Trailer Files
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.
calwf3 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” 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.
ACS FILESTRUCTURE
All WFC3 science data products are two-dimensional images that are stored
in Multi-Extension FITS files, which can be manipulated directly in the
IRAF/STSDAS environment. The structure of these data products is based
on the ACS, NICMOS, and STIS file format. All images taken during an
exposure are bundled in a single FITS file, with each image stored in
a separate FITS image extension.
For more details, please consult the WFC3 instrument handbook at STScI.
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