Description

The ami_analyze step is one of the AMI-specific steps in the ami sub-package that is part of Stage 3 calwebb_ami3 processing. It applies the Lacour-Greenbaum (LG) image plane modeling algorithm to a NIRISS AMI image. The routine computes a number of parameters, including a model fit (and residuals) to the image, fringe amplitudes and phases, and closure phases and amplitudes.

The JWST AMI observing template allows for exposures to be obtained using either full-frame (SUBARRAY=”FULL”) or subarray (SUBARRAY=”SUB80”) readouts. When processing a full-frame exposure, the ami_analyze step extracts and processes a region from the image corresponding to the size and location of the SUB80 subarray, in order to reduce execution time.

Arguments

The ami_analyze step has two optional arguments:

–oversample

The oversampling factor to be used in the model fit (default=3)

–rotation

Initial guess for the rotation of the PSF in the input image, in units of degrees (default=0.0)

Inputs

2D calibrated image

Data model

ImageModel

File suffix

_cal

The ami_analyze step takes a single calibrated image as input, which should be the “_cal” product resulting from calwebb_image2 processing. Multiple exposures can be processed via use of an ASN file that is used as input to the calwebb_ami3 pipeline. The ami_analyze step itself does not accept an ASN as input.

Outputs

LG model parameters

Data model

AmiLgModel

File suffix

_ami

The ami_analyze step produces a single output file, containing the following list of extensions:

  1. FIT: a 2D image of the fitted model

  2. RESID: a 2D image of the fit residuals

  3. CLOSURE_AMP: table of closure amplitudes

  4. CLOSURE_PHA: table of closure phases

  5. FRINGE_AMP: table of fringe amplitudes

  6. FRINGE_PHA: table of fringe phases

  7. PUPIL_PHA: table of pupil phases

  8. SOLNS: table of fringe coefficients

The output file name syntax is exposure-based, using the input file name as the root, with the addition of the association candidate ID and the “_ami” product type suffix, e.g. “jw87600027001_02101_00002_nis_a3001_ami.fits.”

Reference Files

The ami_analyze step uses a THROUGHPUT reference file.

THROUGHPUT Reference File

REFTYPE

THROUGHPUT

Data model

ThroughputModel

The THROUGHPUT reference file contains throughput data for the filter used in the AMI image.

Reference Selection Keywords for THROUGHPUT

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

Instrument

Keywords

NIRISS

INSTRUME, FILTER, 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 THROUGHPUT

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

Keyword

Data Model Name

FILTER

model.meta.instrument.filter

Reference File Format

THROUGHPUT reference files are FITS files with one BINTABLE extension. The FITS primary data array is assumed to be empty. The format of the file is as follows:

EXTNAME

XTENSION

NAXIS

Dimensions

Data type

THROUGHPUT

BINTABLE

2

TFIELDS = 2

N/A

The table extension contains two columns, giving wavelength and throughput values for a particular filter:

Column name

Data type

Units

wavelength

float

Angstroms

throughput

float

(unitless)