GAIN reference file
- REFTYPE:
GAIN
- Data model:
The GAIN reference file contains a pixel-by-pixel gain map, which can be used to convert pixel values from units of DN to electrons. The gain values are assumed to be in units of e/DN.
Reference Selection Keywords for GAIN
CRDS selects appropriate GAIN references based on the following keywords. GAIN is not applicable for instruments not in the table. All keywords used for file selection are required.
Instrument |
Keywords |
---|---|
FGS |
INSTRUME, DETECTOR, SUBARRAY, DATE-OBS, TIME-OBS |
MIRI |
INSTRUME, DETECTOR, SUBARRAY, DATE-OBS, TIME-OBS |
NIRCam |
INSTRUME, DETECTOR, SUBARRAY, DATE-OBS, TIME-OBS |
NIRISS |
INSTRUME, DETECTOR, SUBARRAY, 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 GAIN
In addition to the standard reference file keywords listed above, the following keywords are required in GAIN reference files, because they are used as CRDS selectors (see Reference Selection Keywords for GAIN):
Keyword |
Data Model Name |
---|---|
DETECTOR |
model.meta.instrument.detector |
SUBARRAY |
model.meta.subarray.name |
BUNIT1 |
model.meta.bunit_data |
1 BUNIT is not used as a CRDS selector, but is required in the “SCI” extension header of GAIN reference files to document the units of the data. The expected value is “ELECTRONS/DN”.
Reference File Format
GAIN reference files are FITS files with a single IMAGE extension. The FITS primary data array is assumed to be empty. The characteristics of the FITS extensions are as follows:
EXTNAME |
XTENSION |
NAXIS |
Dimensions |
Data type |
---|---|---|---|---|
SCI |
IMAGE |
2 |
ncols x nrows |
float |