Exposure Level Processing

Class:: romancal.pipeline.ExposurePipeline
Alias:: exposure_pipeline

The ExposurePipeline applies detector-level corrections to all WFI exposure types. It is applied to one exposure at a time. It is sometimes referred to as “ramps-to-slopes” processing, because the input raw data are in the form of ramps containing accumulating counts from the non-destructive detector readouts and the output is a corrected countrate (slope) image.

The steps applied depend on the exposure type, as shown in the table below.

Step	WFI-Image WFI-LOLO	WFI-WFSC (WFSC only)	WFI-Other
dq_init	✓	✓	✓
saturation	✓	✓	✓
refpix	✓	✓	✓
dark_decay	✓	✓	✓
wfi18_transient	✓	✓	✓
linearity	✓	✓	✓
ramp_fitting	✓	✓	✓
dark_current	✓	✓	✓
assign_wcs	✓	✓	✓
photom	✓	✓	✓
flatfield	✓	✓
source_catalog	✓
tweakreg	✓

WFI-Other covers WFI_SPECTRAL, WFI_FLAT, WFI_IM_DARK, and WFI_SP_DARK exposure types, which stop after photom.

Arguments

The exposure pipeline has no arguments

Inputs

For more details about step arguments (including datatypes, possible values and defaults) see romancal.pipeline.ExposurePipeline.spec.

--on_disk: When True the input association will be opened in a way that uses temporary files to avoid keeping all input models in memory.

You can see the options for strun using:

strun –help roman_elp

and this will list all the strun options as well as the step options for the roman_elp.

3D raw data

Data model:: RampModel
File suffix:: _uncal

The input to the ExposurePipeline can be a single raw exposure, e.g. “r0008308002010007027_0019_wfi01_uncal.asdf”, which contains the original raw data from all of the detector readouts in the exposure ( ngroups x ncols x nrows ). The raw data may also be input using an association file.

If the ExposurePipeline is given a single file the final alignment to Gaia will be done with the sources found in the exposure. If multiple exposures exist in the association file then the final alignment will use all the sources found in the exposures (see tweakreg).

Note that in the operational environment, the input will be in the form of a RawScienceModel, which only contains the 3D array of detector pixel values, along with some optional extensions. When such a file is loaded into the pipeline, it is immediately converted into a RampModel, and has all additional data arrays for errors and Data Quality flags created and initialized.

When the ExposurePipeline processes a fully saturated input (all pixels flagged as saturated), the corresponding output image will:

contain all 0 data arrays
contain all 0 variance arrays
not be processed by steps beyond saturation

Fully saturated exposures are skipped by tweakreg individually; other exposures in the same association are still aligned normally.

Outputs

2D Image model

Data model:: ImageModel
File suffix:: _cal

Catalog file (SourceCatalog)

The catalog data is in

Data model:: astropy.table.Table
File suffix:: _cat

Segmentation Map (SegmentationMapModel)

The segmentation map is

Data model:: MosaicSegmentationMapModel
File suffix:: _segm

Result of applying all pipeline steps up through the tweakreg step is to produce calibrated data with the image WCS aligned to Gaia, and is 2D image data, which will have one less data dimensions as the input raw 3D data. In addition to being a 2-dimensional image the output from the pipeline has the reference pixels removed from the edges of the science array and saved as additional 3D arrays. The source catalog and segmentation map from the individual exposues is also saved.

WFI Level 1/Level 2 WCS (WfiWcsModel)

Data model:: WfiWcsModel
File suffix:: _wcs

Contains a copy of the final, Gaia-aligned, Level 2 Generalized World Coordinate System (GWCS) information along with a modified Level 1 GWCS which accounts for the border pixels. The Level 1 GWCS can be used directly with the related Level 1 product. This file also contains header metadata from the L2 image, which may include, for example, updated ephemeris information relative to the original raw file. WfiWcs files are produced for both imaging and spectroscopic observations.