Reference File¶
The dark step uses a DARK reference file.
DARK Reference File¶
- REFTYPE
DARK
- Data models
The DARK reference file contains pixel-by-pixel and frame-by-frame dark current values for a given detector readout mode.
Reference Selection Keywords for DARK¶
CRDS selects appropriate DARK references based on the following keywords. DARK is not applicable for instruments not in the table.
Instrument |
Keywords |
|---|---|
FGS |
INSTRUME, DETECTOR, READPATT, SUBARRAY, DATE-OBS, TIME-OBS |
MIRI |
INSTRUME, DETECTOR, READPATT, SUBARRAY, DATE-OBS, TIME-OBS |
NIRCam |
INSTRUME, DETECTOR, EXP_TYPE, NOUTPUTS, 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 DARK¶
In addition to the standard reference file keywords listed above, the following keywords are required in DARK reference files, because they are used as CRDS selectors (see Reference Selection Keywords for DARK):
Keyword |
Data Model Name |
Instruments |
|---|---|---|
DETECTOR |
model.meta.instrument.detector |
All |
EXP_TYPE |
model.meta.exposure.type |
NIRCam |
NOUTPUTS |
model.meta.exposure.noutputs |
NIRCam |
READPATT |
model.meta.exposure.readpatt |
FGS, MIRI, NIRISS, NIRSpec |
SUBARRAY |
model.meta.subarray.name |
All |
SUBSTRT1 |
model.meta.subarray.xstart |
NIRSpec |
SUBSTRT2 |
model.meta.subarray.ystart |
NIRSpec |
SUBSIZE1 |
model.meta.subarray.xsize |
NIRSpec |
SUBSIZE2 |
model.meta.subarray.ysize |
NIRSpec |
Reference File Format¶
DARK reference files are FITS format, with 3 IMAGE extensions and 1 BINTABLE extension. The FITS primary data array is assumed to be empty. The format and content of the files is different for MIRI than the near-IR instruments, as shown below.
Near-IR Detectors¶
Characteristics of the three IMAGE extensions for DARK files used with
the Near-IR instruments are as follows (see DarkModel):
EXTNAME |
NAXIS |
Dimensions |
Data type |
|---|---|---|---|
SCI |
3 |
ncols x nrows x ngroups |
float |
ERR |
3 |
ncols x nrows x ngroups |
float |
DQ |
2 |
ncols x nrows |
integer |
DQ_DEF |
2 |
TFIELDS = 4 |
N/A |
MIRI Detectors¶
The DARK reference files for the MIRI detectors depend on the integration number,
because the first integration of MIRI exposures contains effects from the detector
reset and are slightly different from subsequent integrations. Currently the MIRI
DARK reference files contain a correction for only two integrations: the first
integration of the DARK is subtracted from the first integration of the science data,
while the second DARK integration is subtracted from all subsequent science integrations.
The format of the MIRI DARK reference files is as follows
(see DarkMIRIModel):
EXTNAME |
NAXIS |
Dimensions |
Data type |
|---|---|---|---|
SCI |
4 |
ncols x nrows x ngroups x nints |
float |
ERR |
4 |
ncols x nrows x ngroups x nints |
float |
DQ |
4 |
ncols x nrows x 1 x nints |
integer |
DQ_DEF |
2 |
TFIELDS = 4 |
N/A |
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.