PSF Reference File

REFTYPE:

PSF

Data model:

EpsfRefModel

The PSF reference file contains a grid of point spread images for a given detector position, filter, and spectral type.

Reference Selection Keywords for PSFs

CRDS selects appropriate PSF references based on the following metadata attributes. All attributes used for file selection are required.

Instrument	Keywords
WFI	instrument, detector, filter, date, time

Standard ASDF metadata

The following table lists the attributes that are required to be present in all reference files. The first column shows the attribute in the ASDF reference file headers, which is the same as the name within the data model meta tree (second column). The second column gives the roman data model name for each attribute, which is useful when using data models in creating and populating a new reference file.

Attribute	Fully Qualified Path
author	model.meta.author
model_type	model.meta.model_type
date	model.meta.date
description	model.meta.description
instrument	model.meta.instrument.name
reftype	model.meta.reftype
telescope	model.meta.telescope
useafter	model.meta.useafter

NOTE: More information on standard required attributes can be found here: Standard ASDF metadata

Type Specific Keywords for the PSF

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

Keyword	Data Model Name	Instrument
detector	model.meta.instrument.detector	WFI
optical_element	model.meta.instrument.optical_element	WFI

Reference File Format

PSF reference files are ASDF format, with four data objects. The format and content of the file is as follows:

Data	Object Type	Dimensions	Data type
psf	NDArray	3 x 3 x 9 x 391 x 391	float32
extended_psf	NDArray	3641 x 3641	float32
extended_psf_noipc	NDArray	3641 x 3641	float32
psf_noipc	NDArray	3 x 3 x 9 x 391 x 391	float32

The values in the psf and psf_noipc arrays contain a grid of images with three focus positions, three spectral types and nine positions on the detector. The focus is the number of defocus waves in the reference files (0, 1, or 2) and 0 corresponds to in-focus position. The spectral type is in order of [A0V, G2V, and M5V], and grid position is an index related to the meta.pixel_x and meta.pixel_y values in the file metadata. The field of view of the ePSF is 361 oversampled pixels (0.11 native arcseconds / pixel oversampled by a factor of 4 yielding approximately 10 arcseconds on a side), while the extended PSF is 3641 pixels (or approximately 100 arcseconds on a side). The detector positions where the PSFs are simulated are: x = [4.0, 2047.5, 4091.0, 4.0, 2047.5, 4091.0, 4.0, 2047.5, 4091.0], y = [4.0, 4.0, 4.0, 2047.5, 2047.5, 2047.5, 4091.0, 4091.0, 4091.0]. The psf and extended_psf arrays have been convolved with an interpixel capacitance (IPC) kernel to make them more like empirical PSFs (ePSFs) that will be observed on-orbit.

The ASDF file contains four data arrays.