Reference Files
The saturation step uses a SATURATION reference file.
SATURATION Reference File
- REFTYPE:
SATURATION
- Data model:
The SATURATION reference file contains pixel-by-pixel saturation threshold values.
Reference Selection Keywords for SATURATION
CRDS selects appropriate SATURATION references based on the following keywords. SATURATION is not applicable for instruments not in the table. All keywords used for file selection are required.
Instrument |
Keywords |
|---|---|
FGS |
INSTRUME, DETECTOR, DATE-OBS, TIME-OBS |
MIRI |
INSTRUME, DETECTOR, DATE-OBS, TIME-OBS |
NIRCam |
INSTRUME, DETECTOR, DATE-OBS, TIME-OBS |
NIRISS |
INSTRUME, DETECTOR, DATE-OBS, TIME-OBS |
NIRSpec |
INSTRUME, DETECTOR, SUBARRAY, 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 SATURATION
In addition to the standard reference file keywords listed above, the following keywords are required in SATURATION reference files, because they are used as CRDS selectors (see Reference Selection Keywords for SATURATION):
Keyword |
Data Model Name |
Instrument |
|---|---|---|
DETECTOR |
model.meta.instrument.detector |
All |
SUBARRAY |
model.meta.subarray.name |
NIRSpec |
Reference File Format
SATURATION reference files are FITS format, with 2 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 |
DQ |
IMAGE |
2 |
ncols x nrows |
integer |
DQ_DEF |
BINTABLE |
2 |
TFIELDS = 4 |
N/A |
The values in the SCI array give the saturation threshold in units of DN
for each pixel.
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.