Reference Files¶
The superbias subtraction step uses a SUPERBIAS reference file.
SUPERBIAS Reference File¶
- REFTYPE
SUPERBIAS
- Data model
The SUPERBIAS reference file contains a 2-D image of the detector bias (“zeroth” read) structure.
Reference Selection Keywords for SUPERBIAS¶
CRDS selects appropriate SUPERBIAS references based on the following keywords. SUPERBIAS is not applicable for instruments not in the table. All keywords used for file selection are required.
Instrument |
Keywords |
|---|---|
FGS |
INSTRUME, DETECTOR, READPATT, SUBARRAY, DATE-OBS, TIME-OBS |
NIRCam |
INSTRUME, DETECTOR, READPATT, SUBARRAY, DATE-OBS, TIME-OBS |
NIRISS |
INSTRUME, DETECTOR, READPATT, SUBARRAY, DATE-OBS, TIME-OBS |
NIRSpec |
INSTRUME, DETECTOR, READPATT, SUBARRAY, SUBSTRT1, SUBSTRT2, SUBSIZE1, SUBSIZE2, DATE-OBS, TIME-OBS |
Standard Keywords¶
The following table lists the keywords that are required to be present in all reference files. The first column gives the FITS keyword names. The second column gives the jwst data model name for each keyword, which is useful when using data models in creating and populating a new reference file. The third column gives the equivalent meta tag in ASDF reference file headers, which is the same as the name within the data model meta tree (second column).
FITS Keyword |
Data Model Name |
ASDF meta tag |
|---|---|---|
AUTHOR |
model.meta.author |
author |
DATAMODL |
model.meta.model_type |
model_type |
DATE |
model.meta.date |
date |
DESCRIP |
model.meta.description |
description |
FILENAME |
model.meta.filename |
N/A |
INSTRUME |
model.meta.instrument.name |
instrument: {name} |
PEDIGREE |
model.meta.pedigree |
pedigree |
REFTYPE |
model.meta.reftype |
reftype |
TELESCOP |
model.meta.telescope |
telescope |
USEAFTER |
model.meta.useafter |
useafter |
NOTE: More information on standard required keywords can be found here: Standard Required Keywords
Type Specific Keywords for SUPERBIAS¶
In addition to the standard reference file keywords listed above, the following keywords are required in SUPERBIAS reference files, because they are used as CRDS selectors (see Reference Selection Keywords for SUPERBIAS):
Keyword |
Data Model Name |
Instruments |
|---|---|---|
DETECTOR |
model.meta.instrument.detector |
FGS, NIRCam, NIRISS, NIRSpec |
READPATT |
model.meta.exposure.readpatt |
FGS, NIRCam, NIRISS, NIRSpec |
SUBARRAY |
model.meta.subarray.name |
FGS, NIRCam, NIRISS, NIRSpec |
SUBSTRT1 |
model.meta.subarray.xstart |
NIRSpec only |
SUBSTRT2 |
model.meta.subarray.ystart |
NIRSpec only |
SUBSIZE1 |
model.meta.subarray.xsize |
NIRSpec only |
SUBSIZE2 |
model.meta.subarray.ysize |
NIRSpec only |
Reference File Format¶
SUPERBIAS reference files are FITS format, with 3 IMAGE extensions and 1 BINTABLE extension. The FITS primary HDU does not contain a data array. The format and content of the file is as follows:
EXTNAME |
XTENSION |
NAXIS |
Dimensions |
Data type |
|---|---|---|---|---|
SCI |
IMAGE |
2 |
ncols x nrows |
float |
ERR |
IMAGE |
2 |
ncols x nrows |
float |
DQ |
IMAGE |
2 |
ncols x nrows |
integer |
DQ_DEF |
BINTABLE |
2 |
TFIELDS = 4 |
N/A |
The SCI array contains the super-bias image of the detector. The
ERR array contains uncertainties in the super-bias values and the
DQ array contains data quality flags associated with the super-bias
image.
The DQ_DEF extension contains the bit assignments used in the DQ array. It contains the following 4 columns:
TTYPE |
TFORM |
Description |
|---|---|---|
BIT |
integer |
The bit number, starting at zero |
VALUE |
integer |
The equivalent base-10 value of BIT |
NAME |
string |
The mnemonic name of the data quality condition |
DESCRIPTION |
string |
A description of the data quality condition |
NOTE: For more information on standard bit definitions see: Data Quality Flags.