Reference Files
The barshadow step uses a BARSHADOW reference file.
BARSHADOW Reference File
- REFTYPE:
BARSHADOW
- Data model:
Reference Selection Keywords for BARSHADOW
CRDS selects appropriate BARSHADOW references based on the following keywords. BARSHADOW is not applicable for instruments not in the table.
Instrument |
Keywords |
|---|---|
NIRSpec |
INSTRUME, EXP_TYPE, 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 BARSHADOW
In addition to the standard reference file keywords listed above, the following keywords are required in BARSHADOW reference files, because they are used as CRDS selectors (see Reference Selection Keywords for BARSHADOW):
Keyword |
Data Model Name |
|---|---|
EXP_TYPE |
model.meta.exposure.type |
Reference File Format
BARSHADOW reference files are FITS format, with 4 IMAGE extensions. The FITS primary data array is assumed to be empty. The format and content of the file is as follows:
EXTNAME |
XTENSION |
NAXIS |
Dimensions |
Data type |
|---|---|---|---|---|
DATA1X1 |
IMAGE |
2 |
101x1001 |
float |
VAR1X1 |
IMAGE |
2 |
101x1001 |
float |
DATA1X3 |
IMAGE |
2 |
101x1001 |
float |
VAR1X3 |
IMAGE |
2 |
101x1001 |
float |
The slow direction has 1001 rows and gives the dependence of the bar shadow correction on the Y location of a pixel from the center of the shutter. The fast direction has 101 rows and gives the dependence of the bar shadow correction of wavelength. The WCS keywords CRPIX1/2, CRVAL1/2 and CDELT1/2 tell how to convert the pixel location in the reference file into a Y location and wavelength. The initial version of the reference file has Y varying from -1.0 for row 1 to +1.0 at row 1001, and the wavelength varying from 0.6x10-6 m to 5.3x10-6 m.
An example extension header is as follows:
XTENSION |
= |
‘IMAGE ‘ |
/ |
Image extension |
BITPIX |
= |
-64 |
/ |
array data type |
NAXIS |
= |
2 |
/ |
number of array dimensions |
NAXIS1 |
= |
101 |
||
NAXIS2 |
= |
1001 |
||
PCOUNT |
= |
0 |
/ |
number of parameters |
GCOUNT |
= |
1 |
/ |
number of groups |
EXTNAME |
= |
‘DATA1x1 ‘ |
/ |
extension name |
BSCALE |
= |
1.0 |
||
BZERO |
= |
0.0 |
||
BUNIT |
= |
‘UNITLESS’ |
||
CTYPE1 |
= |
‘METER ‘ |
||
CTYPE2 |
= |
‘UNITLESS’ |
||
CDELT1 |
= |
4.7E-08 |
||
CDELT2 |
= |
0.002 |
||
CRPIX1 |
= |
1.0 |
||
CRPIX2 |
= |
1.0 |
||
CRVAL1 |
= |
6E-07 |
||
CRVAL2 |
= |
-1.0 |
||
APERTURE |
= |
‘MOS1x1 ‘ |
||
HEIGHT |
= |
0.00020161 |