FPA Reference File (NIRSpec only)

REFTYPE:

FPA

Data model:

FPAModel

Reference Selection Keywords for FPA

CRDS selects appropriate FPA references based on the following keywords. FPA is not applicable for instruments not in the table. All keywords used for file selection are required.

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

Reference File Format

The FPA reference file stores information on the metrology of the Focal Plane Assembly (FPA), which consists of two Sensor Chip Arrays (SCA), named NRS1 and NRS2.

The reference file contains two fields : “nrs1_model” and “nrs2_model”. Each of them stores the transform (shift and rotation) to transform positions from the FPA to the respective SCA. The output units are in pixels.

nrs1_model:

Transform for the NRS1 detector.

nrs2_model:

Transform for the NRS2 detector.