Wide Field Instrument (WFI)

The Wide Field Instrument (WFI) is Roman’s primary science instrument and enables large scale surveys. The WFI is a 300-megapixel visible-to-NIR imaging camera and slitless spectrometer. In the full Roman Observatory, the WFI is composed of two major components: the Cold Sensing Module (CSM) and the Warm Electronics Module (WEM).

• The CSM is situated between the telescope and spacecraft bus and latched to a structure called the Instrument Carrier (see figure below). At the core of the CSM is a detector array of 18 Teledyne H4RG-10 Sensor Chip Assemblies (SCAs) and their associated readout and control electronics.
• The SCAs in the focal plane array produce an 0.4 x 0.8 deg (0.281 deg² excluding detector gaps) field-of-view, ≈200× larger than Hubble’s WFC3-IR camera but with better sensitivity and comparable spatial resolution.
• Before reaching the detector array, light from Roman’s optical system encounters the Element Wheel Assembly (EWA). The EWA is a rotating wheel that contains multiple filters for imaging and grism and prism dispersers for slitless spectroscopy across the full field.
• The focal plane array is mounted into a mechanism called the Alignment Compensation Mechanism (ACM) that allows for fine focus and alignment.
• The WFI also carries an internal relative calibration system to accurately calibrate and trend detector response, particularly linearity, over the full mission lifetime.
• The WEM provides instrument commanding and mechanism control. It is located in one of the spacecraft bus bays.

The figure below shows the CSM in context with the observatory and provides details on the major subsystems (adapted from Schlieder et al. 2024). The table below provides a top-level overview of WFI parameters that are driven by mission science requirements.

Parameter	Value
Focal Plane Array
Detectors	18 Teledyne H4RG-10 detectors with 4096 x 4096 pixels
Field of View	0.8 deg x 0.4 deg (0.281 deg2, excluding gaps)
Spatial Sampling	0.11 arcsec/pixel
Pixel size	10 μm
Image Stability	1.0 nm RMS wave front error (WFE) in 180 sec
Guiding	Guide star sensing interleaved with science data collection
Element Wheel
Modes	Imaging, spectroscopy, and calibrations
Imaging	8 imaging filters spanning 0.48 to 2.3 μm
Spectroscopy	Prism and grism for full-field, slitless spectroscopy spanning 0.75 to 1.93 μm
Calibrations	Dark element and filter mask diffusers allow darks, flat fields, and other calibrations with WFI's internal relative calibration system
Thermal Control
Cooling Method	Passive cooling via external radiators
Operating Temperature	Multiple thermal zones with detectors at 89.5 K

For more information on the WFI and its subsystems, please refer to Schlieder et al. 2024 and references therein as well as the Science Operations Center Roman WFI Documentation (RDox) pages.

Filters

WFI carries 8 science filters with overlapping band passes spanning 0.48 – 2.3 microns. The filters are located at the telescope exit pupil. They are housed in the element wheel and are rotated into the instrument light path for multiwavelength imaging.

Filter Point Spread Functions

This update is based on the post-CDR optical design. The wavefront error model includes design residuals and Monte Carlo estimates of surface figure errors and alignment tolerances. We plan to issue a new release in 2025 once we have wavefront measurements of the integrated telescope and Wide-Field Instrument.

Point spread functions (PSFs) for the Nancy Grace Roman Space Telescope have been created using WebbPSF version 1.0, a Python-based package. This tool takes into account properties of the telescope and the instruments, including detector pixel scale, rotations, filter profiles, and point source spectra. These are not full optical models, simply a tool that transforms the optical path difference maps, into the resulting Roman PSFs.

The website linked above provides instructions on how to install WebbPSF, how to run it via the Python API, in addition to providing Roman specific examples.

Imaging PSFs were calculated at the center of each SCA and also around the periphery of the focal plane; located at the center of a pixel and at the corner of a pixel.

Filter Parameters

						Corner PSF		Center PSF
Element name	Min (μm)	Max (μm)	Center (μm)	Width (μm)	PSF FWHM (arcsec) *	n eff pixel	Peak Flux	n eff pixel	peak flux
F062	0.48	0.76	0.620	0.280	0.058	7.35	0.20341	3.80	0.49536
F087	0.76	0.977	0.869	0.217	0.073	9.35	0.16517	4.04	0.4838
F106	0.927	1.192	1.060	0.265	0.087	10.96	0.15060	4.83	0.44004
F129	1.131	1.454	1.293	0.323	0.106	11.79	0.14863	6.63	0.36874
F158	1.380	1.774	1.577	0.394	0.128	12.63	0.14343	9.65	0.29081
F184	1.683	2.000	1.842	0.317	0.146	17.15	0.11953	15.52	0.21361
F213	1.95	2.30	2.125	0.35	0.169	20.38	0.10831	20.14	0.17052
F146	0.927	2.000	1.464	1.030	0.105	12.18	0.14521	7.37	0.34546

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Download all the PSF FWHM (arcsec) * [.ZIP]

*Note: PSF FWHM in arcseconds simulated for a detector near the center of the WFI FOV using an input spectrum for a K0V type star. Please click on the FWHM value for each filter to view the simulated PSF.

The above table provides representative PSF FWHM values for a detector (SCA 1) near the center of the WFI FOV. Wavelength distribution is that of a K0V star, sampled over each filter bandpass. N Eff Pix is number of effective pixels (aka noise pixels) under the PSF (1/sum of squares of pixel values). Fluxes normalized at telescope exit pupil. Images are ~7 arcsec square and typically contain 97%-99% of the incident flux. Two cases are provided: at the corner of 4 pixels, and at the center of a pixel.

FWHM (arcsec) of PSF is computed from 8-times oversampled PSF. Gaussian pointing jitter with FWHM = 8 mas is included. The number of noise pixels and maximum flux per pixel are computed on native detector pixels.

Simulated PSFs for different stellar types and all detectors across the focal plane can be found here.

Roman Effective Area Curves

(updated March 2024)

The Roman effective area has been updated to reflect recalibration of the sensor ship assembly (SCA) quantum efficiency, and preliminary updates to the filter, prism, and grism bandpasses. The tables have also been broken out by SCA to illustrate the small differences in QE and the shift in filter bandpasses with field angle. Download the Filter Effective Area tables [.ZIP]

The tables are in ECSV format, which is can be read via astropy.io.ascii.read() and any text editor.

The plot below illustrates both these effects by comparing the effective area for SCAs 1 and 9 for filter F158.

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Download all the PSF FWHM (arcsec) * [.ZIP]

*Note: PSF FWHM in arcseconds simulated for a detector near the center of the WFI FOV using an input spectrum for a K0V type star. Please click on the FWHM value for each filter to view the simulated PSF.

The above table provides representative PSF FWHM values for a detector (SCA 1) near the center of the WFI FOV. Wavelength distribution is that of a K0V star, sampled over each filter bandpass. N Eff Pix is number of effective pixels (aka noise pixels) under the PSF (1/sum of squares of pixel values). Fluxes normalized at telescope exit pupil. Images are ~7 arcsec square and typically contain 97%-99% of the incident flux. Two cases are provided: at the corner of 4 pixels, and at the center of a pixel.

FWHM (arcsec) of PSF is computed from 8-times oversampled PSF. Gaussian pointing jitter with FWHM = 8 mas is included. The number of noise pixels and maximum flux per pixel are computed on native detector pixels.

Simulated PSFs for different stellar types and all detectors across the focal plane can be found here.

Roman Effective Area Curves

(updated March 2024)

The Roman effective area has been updated to reflect recalibration of the sensor ship assembly (SCA) quantum efficiency, and preliminary updates to the filter, prism, and grism bandpasses. The tables have also been broken out by SCA to illustrate the small differences in QE and the shift in filter bandpasses with field angle. Download the Filter Effective Area tables [.ZIP]

The tables are in ECSV format, which is can be read via astropy.io.ascii.read() and any text editor.

The bandpass shifts given here are representative models; these will be updated once the full set of data from the wide-field instrument thermal vacuum test has been obtained and analyzed.

Imaging Sensitivity

Imaging Sensitivity Overview

(Updated June 3, 2024)

The table below gives the 5-sigma AB magnitude limiting sensitivity, for twice the minimum zodiacal light background (roughly equivalent to that obtained at an ecliptic latitude of 25 degrees at a Solar elongation of 90 degrees), for 57 second and one-hour integrations, for point sources and a compact galaxy with half-light radius of 0.3 arcseconds.

S/N was computed for photometric apertures of radius 2 pixels for point sources and 6 pixels for the galaxies.

Filter	F062	F087	F106	F129	F158	F184	F213	F146
Wavelength (microns)	0.48-0.76	0.76-0.98	0.93-1.19	1.13-1.45	1.38-1.77	1.68-2.00	1.95-2.30	0.93-2.00
1 hr, Point	27.97	27.63	27.60	27.60	27.52	26.95	25.64	28.01
1 hr, r50=0.3”	26.70	26.38	26.37	26.37	26.37	25.95	24.71	26.84
57s, Point	24.77	24.46	24.46	24.43	24.36	23.72	23.14	25.37
57s, r50=0.3”	23.53	23.23	23.26	23.24	23.24	22.76	22.23	24.22

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Scalings for other deep cases: The flux density limit for other deep integrations, between about ten minutes and tens of hours, can be estimated from the 1 hour depths using a flux ∝ t^-1/2 scaling. For integrations below about 10 minutes, this scaling becomes over-optimistic by > 30% due to read noise and overheads. Limits for a half-light radius of 0.2” are slightly closer to the 0.3” case than the point source case. For more extended sources, the limiting flux density f_ν,lim for fixed SNR and integration time should be scaled from the 0.3” case approximately as f_ν,lim∝r₅₀ or ΔAB_lim=2.5 log(0.3"/r₅₀). Reducing the assumed zodiacal background from 2x to 1.44x minimum improves deep imaging flux limits by about 0.15 mag for the F062 through F158 filters, 0.08 mag for F184 and F146, and negligibly for F213.

Fast/Wide Limit: The final two lines in the table give magnitude limits achieved at 5σ in 55 seconds (with a single exposure). At this integration time, Roman can cover approximately 8 contiguous square degrees per hour in one spectral element, and slew-and-settle overheads slightly exceed integration time. There is little point considering faster survey speeds, because sensitivity drops rapidly for modest increases in survey speed at yet shorter integrations.

Zodiacal Light and Thermal Background

(Updated June 3, 2024)

The tables below provides the count rate per pixel at minimum Zodiacal light in each filter and the estimated thermal background. For observations at high galactic latitudes, the Zodi intensity is typically ~1.5x the minimum. For observation into the galactic bulge, the Zodi intensity is typically 2.5-7x the minimum.

Count rate per pixel at minimum Zodiacal Light
F062	F087	F106	F129	F158	F184	F213	F146
0.25	0.251	0.277	0.267	0.244	0.141	0.118	0.781

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Internal thermal backgrounds (count rate per pixel)
F062	F087	F106	F129	F158	F184	F213	F146
0.003	0.003	0.003	0.003	0.048	0.155	4.38	1.03

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Imaging Sensitivity Calculator

(Note: data files have *not* yet been updated)

On this page you will find tools designed to help you, the user, calculate the exposure time required for a given source at a given signal to noise, or vice versa.

We have provided a Jupyter notebook which walks through each step of the calculation, and a python script that will open a GUI in which you can input your objects information.

To run both scripts you will need to download the accompanying data files.

Both the notebook and the GUI require the user to specify the filter, zodiacal light contribution, type of source, fitting method, and signal to noise. In this notebook we will be doing exposure time calculations for point sources, and extended sources with half-light radii of 0.2 arcsec or 0.3 arcsec.

• Filters: F062, F087, F106, F129, F158, F184, F146, F213
• Zodiacal light contributions (multiples of the minimum): 1.2, 1.4, 2.0, 3.5
• Source: point sources, objects with a half-light radius (HLR) = 0.2", objects with a HLR = 0.3"
  • Fit with a PSF (Point source only)
  • Fit with a 2 pixel circular aperture (Point source & HLR = 0.2")
  • Fit with a 3 pixel circular aperture
  • Fit with a 4 pixel circular aperture
  • Fit with a 5 pixel circular aperture (HLR = 0.3" only)
  • Fit with a 6 pixel circular aperture (HLR = 0.2" & 0.3" only)
• S/N: 5, 10, 15, 20, 50

The exposure times used within these calculations are quantized in multiples of 3 readout frames, with the number of visits/dithers being 1.

An example of using the Jupyter notebook is provided here.

Spectroscopy

WFI carries 2 dispersive elements for slitless, multi-object spectroscopy. The grism band pass spans 1.0 – 1.93 microns and has a resolution of ~600. The prism band pass spans 0.75 – 1.80 microns and has a resolution of ~100. The dispersing elements are housed in the element wheel and are rotated into the instrument light path for slitless spectroscopy across the WFI FOV.

Grism and Prism parameters

Element name	Min (μm)	Max (μm)	Center (μm)	Width (μm)	R
G150	1.0	1.93	1.465	0.930	461 * wavelength [microns]
P127	0.75	1.80	1.275	1.05	80-180 (2pix)

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Grism and Prism Effective Area Curves

The effective area as a function of wavelength for the filters, grism, and prism are available in tabular form here.

Grism and Prism zodiacal light

The table below provides the count rate per pixel at minimum zodiacal light for the grism and prism. For observations at high galactic latitudes, the Zodi intensity is typically ~1.5x the minimum. For observation into the galactic bulge the Zodi intensity is typically 2.5-7x the minimum.

Count rate per pixel at minimum zodiacal light
Grism	Prism
0.65	0.95

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Grism Spectroscopy Sensitivity

(updated June 11, 2024)

The Roman WFI slitless grism has a spectral range of 1.00-1.93 microns and a dispersion of about 1.1 nm/pixel, essentially independent of wavelength, yielding a 2-pixel resolving power of R = λ / δλ = 460 λ / μm for a point source. Table gives 5-sigma detection limits for a one-hour exposure time with zodiacal light background at twice the minimum intensity. This is representative of an ecliptic latitude of 25 degrees and 90 degrees ecliptic longitude relative to the Sun (the middle of the object visibility window). Typical HLWAS backgrounds are ~30% lower.

For emission lines, the values are integrated line fluxes in units of 10^-17 ergs/cm²/sec.

For continua, the values are the AB magnitude at which S/N=5 per pixel.

The values are averages over all 18 detectors; typical variations from one detector to another are 0.05 to 0.1 mag for the continuum cases and ~10% for the emission line limits.

5σ limits for Roman WFI grism in 1 hour on source, 2x minimum zodiacal background.Emission line limits are in units of 10-17 erg cm-2 s-1, and continuum limits are in AB mags for 1 pixel
Wavelength (microns)	1.05	1.1	1.2	1.3	1.4	1.5	1.6	1.7	1.8	1.9
fline,17, r50=0; 1 hour	5.9	4.7	3.6	3.2	3.0	3.1	3.3	3.7	3.4	4.7
mAB, r50=0; 1 hour	21.3	21.5	21.6	21.6	21.5	21.3	21.2	21.0	20.8	20.4
fline,17, r50=0.3"; 1 hour	16.1	12.9	9.8	8.7	7.6	8.1	8.4	8.9	8.5	11.7
mAB (2 pix), r50=0.3",1 hour	20.5	20.6	20.8	20.7	20.6	20.5	20.3	20.2	20.0	19.6

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Sensitivities for other integration times (between a few minutes and tens of hours) and zodiacal backgrounds can be scaled from the above using f _lim∝t^-1/2 b^1/2, where t is integration time and b the zodiacal background level. Because this is slitless spectroscopy, the scaling of sensitivity with size for r∝r₅₀ > 0.3" differs between line and continuum sensitivity, with limiting behaviors of flne ∝r₅₀, and f_cont ∝r₅₀^1/2.

Prism Spectroscopy Sensitivity

(updated June 11, 2024)

The Roman WFI slitless prism has a spectral range of 0.75-1.80 microns and a resolution that is strongly wavelength dependent, with 80 < λ / δλ < 180. The highest resolution is at the blue end of the prism wavelength coverage. In addition to its lower dispersion, the prism has higher throughput than the grism, making it more sensitive to continuum. The table below has AB magnitude at which S/N=5 per pixel (not per 2 pixels as earlier), at zodiacal light at twice minimum. This is representative of an ecliptic latitude of 25 degrees and 90 degrees ecliptic latitude relative to the Sun (middle of the object visibility window). Typical HLWAS backgrounds are ~30% lower.

These are averages over all 18 detectors; typical variations from one detector to another are 0.05 to 0.1 mag.

5σ limits for Roman WFI prism, 2x minimum zodiacal background
Wavelength	0.80	1.00	1.20	1.40	1.60	1.75
Δλ (for 1 pixel, in nm)	2.2	4.4	5.6	8.2	9.3	9.1
mAB(1 pix), r50=0; 1 hour	22.6	23.2	23.4	23.4	23.3	23.3
mAB(1 pix), r50=0.3"; 1 hour	22.0	22.6	22.8	22.8	22.8	22.7
mAB(1 pix), r50=0; 62 sec	19.9	20.4	20.6	20.7	20.6	20.5
mAB(1 pix), r50=0.3"; 62 sec	19.3	19.9	20.1	20.1	20.1	20.0

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The same scalings that apply to grism spectroscopy can be used to scale other deep prism sensitivities from the 1-hour case.

Grism and Prism dispersion

The grism has constant dispersion and linearly increasing resolving power. The prism provides higher throughput and lower dispersion than the grism. The prism dispersion varies with wavelength and varies slightly with field angle.

Focal Plane System

Updated January 2025

Roman/WFI Focal Plane System (FPS) Sensor Chip Assembly (SCA) Performance Measurements

These measurements were performed on either individual flight SCAs in the NASA Goddard Detector Characterization Lab (DCL) at a temperature of 95 K or on the full flight focal plane during WFI Thermal Vaccuum Test #2 (TVAC2) in the nominal operation (NomOp) test plateau at a temperature of 89.5 K. The test parameters for each performance measurement are noted in the descriptions. In these data tables individual detectors are described by either their Sensor Control Unit (SCU) number, which defines their position in the focal plane array as an integer 1 through 18, or their SCA serial number, which is a 5 digit integer that defines each individual detector. Please refer to the SCU to SCA mapping table and labeled diagram of the flight focal plane array for reference.

Roman/WFI SCU to SCA mapping

Sensor control unit (SCU) number to sensor ship assembly (SCA) serial number mapping.

SCU#	SCA
1	22081
2	21815
3	21946
4	21115
5	21816
6	20663
7	22069
8	21641
9	21813
10	22078
11	21947
12	20829
13	22067
14	21814
15	21645
16	21643
17	21319
18	20833

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WFI CDS Noise Summary

Roman/WFI TVAC2 Nominal Operation (at 89.5 K) correlated double sampling (CDS) noise measurements (mean and medians) for each SCA.

SCU	SCA	CDS Noise - Median (e-)	CDS Noise - Mean (e-)
1	22081	17.49	17.92
2	21815	14.2	14.43
3	21946	14.7	15.34
4	21115	15.76	16.33
5	21816	13.64	15.93
6	20663	13.65	14.06
7	22069	13.21	13.63
8	21641	12.49	12.72
9	21813	12.39	12.57
10	22078	15.75	16.17
11	21947	13.94	14.25
12	20829	13.73	13.88
13	22067	16.17	16.56
14	21814	13.46	13.68
15	21645	13.46	13.72
16	21643	13.49	13.74
17	21319	12.64	12.82
18	20833	12.42	12.59
All Detectors (MPA)	-	13.81	14.46

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WFI Total Noise

Roman/WFI TVAC2 Nominal Operation (89.5 K) total noise measurements (means, medians, and percentage of pixels passing the total noise requirement) for each SCA.

Roman/WFI total noise measured for each Sensor Control Unit (SCU). Total noise data were acquired from WFI TVAC2 measurements of 100 total exposures, each with a ~170-second integration time, consisting of 55 non-destructive reads and 0 skip frames. Specifically, 50 exposures were taken with the Guide Window (GW) at the bottom left of each sensor chip assembly, and 50 with the GW at the top right. Data analysis included top and column reference pixel correction (using a Savitzky-Golay filter), slope calculation of digital number per unit time per pixel using all frames, and total noise calculation per pixel as the standard deviation of the slopes multipliedby the total exposure time (~170-seconds). A global conversion gain was then applied to convert the results to electrons.

SCU	SCA	Total Noise - median (e-)	Total Noise - mean (e-)	Percentage Passing Requirement (%)
1	22081	6.67	7.52	98.86
2	21815	5.6	6.02	99.59
3	21946	5.76	6.19	99.45
4	21115	5.9	6.5	99.53
5	21816	5.76	6.38	99.48
6	20663	5.42	5.97	99.48
7	22069	5.38	5.99	99.37
8	21641	5.13	5.54	99.58
9	21813	5.33	5.7	99.62
10	22078	6.1	6.85	98.69
11	21947	5.86	6.25	99.52
12	20829	5.51	5.9	99.64
13	22067	6.25	6.85	99.08
14	21814	5.41	5.85	99.59
15	21645	5.31	5.75	99.58
16	21643	5.37	5.8	99.56
17	21319	5.14	5.54	99.62
18	20833	5.17	5.6	99.56
All Detectors (MPA)	-	5.58	6.12	99.43

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WFI Dark Current Summary

Roman/WFI TVAC2 Nominal Operation (89.5 K) dark current measurements (means, medians, and percentage of pixels passing the dark current requirement) for each SCA.

NOTE: These measurements are representative of the instrument internal thermal background rather than the true dark current floor of the detectors.

SCU	SCA	Dark Current - Median (e-/s)	Dark Current - Mean (e-/s)	Percentage Passing Requirement (%)
1	22081	0.019	0.049	99.63
2	21815	0.018	0.023	99.95
3	21946	0.019	0.026	99.95
4	21115	0.018	0.038	99.85
5	21816	0.030	0.042	99.84
6	20663	0.016	0.028	99.83
7	22069	0.027	0.044	99.78
8	21641	0.016	0.022	99.94
9	21813	0.017	0.019	99.97
10	22078	0.012	0.033	99.74
11	21947	0.029	0.035	99.94
12	20829	0.020	0.022	99.97
13	22067	0.013	0.023	99.89
14	21814	0.018	0.024	99.94
15	21645	0.016	0.020	99.95
16	21643	0.017	0.023	99.94
17	21319	0.013	0.016	99.98
18	20833	0.015	0.018	99.96
All Detectors (MPA)	-	0.018	0.028	99.89

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WFI Persistence Summary

Roman/WFI TVAC2 Nominal Operation (89.5 K) persistence measurements as a function of time was measured using 10 regularly spaced darks spanning a total time of 1770 secs (~30 min) following exposures of 56 frames each for each SCA. The detectors were exposed to ~900 e-/s flat field illumination, for a total of ~159 ke- of charge accumulation.

Time (sec)	SCU 1	SCU 2	SCU 3	SCU 4	SCU 5	SCU 6	SCU 7	SCU 8	SCU 9	SCU 10	SCU 11	SCU 12	SCU 13	SCU 14
177.072	0.146235	0.26914	0.208909	0.715303	0.166129	0.321581	0.170376	0.221845	0.249611	0.257818	0.229222	0.568741	0.276093	0.178377
354.144	0.044841	0.080633	0.059426	0.241064	0.0463	0.10913	0.049536	0.064649	0.07482	0.07682	0.069049	0.184668	0.090751	0.051928
531.216	0.023507	0.045668	0.03181	0.145959	0.022286	0.068685	0.027701	0.039115	0.040834	0.048665	0.035978	0.111288	0.052541	0.024169
708.288	0.016631	0.031565	0.021515	0.107611	0.015596	0.051404	0.017754	0.025009	0.028098	0.030286	0.025927	0.078931	0.035089	0.018905
885.36	0.009396	0.023053	0.01332	0.080936	0.011316	0.037807	0.01423	0.017882	0.020321	0.024215	0.018094	0.064139	0.028408	0.011699
1062.432	0.00984	0.016082	0.008898	0.06767	0.009273	0.031754	0.011129	0.014292	0.014158	0.020825	0.014174	0.051971	0.024368	0.008673
1239.504	0.00582	0.014848	0.008599	0.058597	0.005292	0.026527	0.008026	0.011552	0.0108	0.015552	0.010313	0.044002	0.016293	0.007313
1416.576	0.006392	0.01378	0.003147	0.050338	0.006203	0.024131	0.001806	0.008925	0.008713	0.014692	0.007939	0.03745	0.016612	0.004375
1593.648	0.003686	0.008991	0.002982	0.043606	0.002584	0.022399	0.009896	0.008839	0.007807	0.011118	0.006973	0.03421	0.013128	0.005231
1770.72	0.003665	0.006856	0.006162	0.038372	0.002049	0.017933	0.005152	0.004193	0.006178	0.011545	0.005599	0.027749	0.009889	0.002241

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Roman/WFI TVAC2 Nominal Operation (89.5 K) exponential decay fits to persistence measurements as a function of time for each SCA. The median persistence (e^-/s over the dark current) was fit to an exponential function with this form: a*e^-bx+d*e^-ex+c, where x is the time in the decay curve and a, b, c, d, and e are fit coefficients provided in this file.

SCU	a	b	c	d	e
1	0.0630975242491005	0.00223961641358588	0.0025742933824052	0.746862190043635	0.011286859153504
2	0.113667333605889	0.00208090919789521	0.00529851744032986	1.63240804741764	0.012290801561742
3	0.127692713448231	0.0028105284087841	0.002995637210518	1.79386542406018	0.0148971770132734
4	0.317245856240149	0.0020385294263819	0.0313180347386418	3.84258893619047	0.0119526816052686
5	0.0399074220360969	0.0010724842266948	-0.00399342219621827	0.818575758396395	0.0100903092011291
6	0.171722202455368	0.00229210782641212	0.0165894251978556	2.23092490376614	0.0138939156373566
7	0.0903847550202783	0.00265170572847035	0.00464743580396528	1.24816990075988	0.0137579427881678
8	0.120784603994506	0.00245260186948826	0.00484601419324385	2.08785922359341	0.0153109677593873
9	0.116569528810883	0.00226588275130876	0.00414036289741852	1.52550646007652	0.0124780793195191
10	0.168943431158506	0.00288223884036085	0.0108454245616368	4.10029537346811	0.0188524408598509
11	0.0819994803715525	0.00184109607970523	0.00230678758276112	1.17683690959174	0.0110023229183419
12	0.219784999387394	0.00185549271970522	0.0213015004890999	3.04482947488278	0.0116175577250163
13	0.097603576989658	0.00163228812268123	0.00539309058027533	1.26391264016757	0.0104807084599246
14	0.0493188990667302	0.00151680485718246	-0.000556202364831174	0.852045139438995	0.0101491228354148
15	0.0554350616724502	0.00227001770532573	0.00342068217961765	0.880160085914408	0.0110268563640265
16	0.0847549639343177	0.00193252760814128	0.00346770668447426	1.20674682246829	0.0118640541303733
17	0.062650881955819	0.00163596315647808	0.000329354246793926	1.27435292812059	0.011155677866177
18	0.175415985545229	0.00182390269280901	0.0163324746934558	2.39421963631299	0.0134505500033584

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WFI Quantum Efficiency

Roman/WFI Detector Characterization Lab measurements of the median quantum efficiency (QE) versus wavelength (linearly interpolated) for each SCA.

For the measured quantum efficiency of each SCA versus wavelength (measured every 10 nm), please see this machine-readable table.

Short and Long Wavelength Quantum Efficiencies

Wavelength Range	Mean Quantum Efficiency	Median Quantum Efficiency
wavelengths < 900 nm	0.694	0.718
900 <= wavelengths <= 2200 nm	0.887	0.888

The mean and median quantum efficiencies for all WFI SCAs for wavelengths < 900 nm and also 900 <= wavelengths <= 2200 nm.

Short and Long Wavelength Cutoffs

Wavelengths between which the quantum efficiency >=50% for each Sensor Control Unit (SCU).

SCU	Short (nm)	Long (nm)
1	560	2480
2	530	2480
3	530	2490
4	530	2480
5	530	2520
6	520	2480
7	530	2510
8	530	2470
9	530	2480
10	530	2440
11	530	2520
12	530	2500
13	520	2450
14	530	2480
15	530	2480
16	520	2470
17	530	2460
18	570	2470
Median	530	2480

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WFI Number of Pixels that Meet Requirements

Roman/WFI TVAC2 Nominal Operation (89.5 K) pixel operability statistics. For each SCA this includes the number of pixels deemed inoperable, which do not meet requirements ("bad pixels"), and the percentage of pixels deemed operable that do meet requirements ("good pixels") for each SCA. The performance metrics that can contribute to a pixel being inoperable are dark current, total noise, linearity, persistence, QE, flat field response, gain, and electrical connectivity.

NOTE: SCU/SCA 4/21115 has a significantly lower operable pixel fraction due to an extended region of the detector with persistence that is somewhat larger than the requirement.

SCU	SCA	Number of Bad Pixels	Percentage Good Pixels (%)
1	22081	374528	97.76
2	21815	107330	99.36
3	21946	175996	98.95
4	21115	2548467	84.75
5	21816	114616	99.31
6	20663	130840	99.22
7	22069	236249	98.59
8	21641	129869	99.22
9	21813	98921	99.41
10	22078	258521	98.45
11	21947	132721	99.21
12	20829	85538	99.49
13	22067	315293	98.11
14	21814	116282	99.3
15	21645	87095	99.48
16	21643	93282	99.44
17	21319	94341	99.44
18	20833	135371	99.19
All Detectors (MPA)	-	-	98.26

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Version History

Release Number	Date	High-level Release Notes
v1.3	August 13, 2025	Add version numbering language and fix jitter.
v1.2	June 30, 2025	Added WFI Technical Overview page
v1.1	January 29, 2025	Added WFI FPS information and measurements from TVAC2
v1.0	August 28, 2024	Initial release of Roman Technical Information

Please note: these release notes are at a very high level. For all of the details and changes for each release, please visit our Roman Technical Information GitHub release page.