READNOISE Reference File

REFTYPE:

READNOISE

Data model:

ReadnoiseModel

The READNOISE reference file contains a pixel-by-pixel map of read noise, which is used in estimating the expected noise in each pixel.

Reference Selection Keywords for READNOISE

CRDS selects appropriate READNOISE references based on the following keywords. READNOISE 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
MIRI	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, 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 READNOISE

In addition to the standard reference file keywords listed above, the following keywords are required in READNOISE reference files, because they are used as CRDS selectors (see Reference Selection Keywords for READNOISE):

Keyword	Data Model Name
DETECTOR	model.meta.instrument.detector
READPATT	model.meta.exposure.readpatt
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 READNOISE reference files to document the units of the data. The expected value is “DN”.

Reference File Format

The READNOISE reference file is a FITS file with a single IMAGE extension, which contains a 2-D floating-point array of read noise values per pixel. The units of the read noise should be DN and should be the CDS (Correlated Double Sampling) read noise, i.e. the effective noise between any pair of non-destructive detector reads. The FITS primary HDU does not contain a data array. The characteristics of the FITS extensions are as follows:

EXTNAME	XTENSION	NAXIS	Dimensions	Data type
SCI	IMAGE	2	ncols x nrows	float