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The Pandeia engine of the Exposure Time Calculator is released to the community to support users who wish to script their calculations, run more extensive parameter space studies, and have more direct control of their scenes. We also recognize that the community has developed more extensive wrappers and public tools that depend on the Pandeia engine.

This page is intended to facilitate communication with developers in the community with Pandeia engine dependencies.



The latest release of the Pandeia engine is 1.6 3.2 (JWST), 3.1 (Roman).

Warning
titleRoman
Roman users must continue to use v1.6; there is no v1


.6.1 release for Roman.


Next Planned Release

The next planned release is 1.7, expected in late September 2021.

Included in the next release:

Breaking ChangesJETC-1750JWST RomanRefactor: The DetectorSignal, CombinedSignal, and CalculationConfig classes are now defined in signal.py; the DetectorNoise class is defined in noise.py; etc3d.py now contains only calculate_sn, calculate_contrast, and calculate_time.JETC-1837JWST RomanThe det_pars section of the configuration file is now 'detector', and has entries for the distinct different types of detector (for instance, NIRCam sw and lw; where sw corresponds to NRCA1-A4, and lw to NRCA5). The 'aperture_config' configuration now contains a detector keyword to indicate which detector each aperture belongs to.JETC-1663JWST RomanRefactor: ExposureSpec now contains only the functions necessary to compute MultiAccum exposure times; it has child classes for H2RG, H4RG, and SiAs.
The noise-computing methods previously in ExposureSpec have been moved to a new class, Detector (with child classes for H2RG, H4RG, and SiAs detectors) along with the calc_cr_loss method previously in DetectorNoise. The Detector instance for a calculation can be accessed from a DetectorSignal as DetectorSignal.the_detector; exposure parameters in ExposureSpec can now be accessed from DetectorSignal as DetectorSignal.the_detector.exposure_spec
The Roman WFI is now properly identified as an H4RG detector, rather than an H2RG. At present, H4RG is identical to H2RG.

release of the Pandeia Engine will be for the JWST Cycle 4 call for proposals.

We will update this page with the list of new items for the next release as they are worked.

Tickets in the upcoming release include:

KeyMissionDescription
JETC-2897JWST

The NIRSpec "msa" mode ("mos" in the webapp) has been renamed to "mos", internally.

The NIRCam "ssgrism" mode ("lw_tsgrism" in the webapp) has been renamed to "lw_tsgrism".

Though old input dictionaries will continue to function until ETC 5.0, anything using build_default_calc() will need to update to use the new names. 

JETC-3058JWST, RomanThe "total_exposure_time" in the "information" report dictionary now takes into account the number of on-source dithers.
JETC-3056JWSTDuty cycle is now an accurate representation of the fraction of exposure time spent collecting photons.
JETC-4374JWSTNIRCam reference data has been updated based on recent calibrations
JETC-4387JWST, RomanA warning will be triggered if the aperture or sky region/annulus is smaller than a pixel.
JETC-330JWSTNew mode: nircam sw_tsgrism. This is the Dispersed Hartmann Sensor (DHS) spectroscopic mode. There is one available disperser: dhs0; and four apertures corresponding to the number of DHS stripes coadded into the final image: dhs0spec2 uses stripes 4 and 7 and must be paired with subarray sub40stripe1_dhs, dhs0spec4 uses stripes 2, 4, 7, and 8 and must be paired with subarray sub80stripe2_dhs; dhs0spec8 uses stripes 2, 3, 4, 5, 7, 8, 9, 10 and must be paired with either subarray sub160stripe4_dhs or sub256stripe4_dhs. For estimations of saturation, use the dhs0bright aperture (stripe 7) and any of the above subarrays. All wide-band sw filters can be used with sw_tsgrism.

lw_tsgrism now allows the new DHS subarrays (sub40stripe1_dhs, sub80stripe2_dhs, sub160stripe4_dhs, sub256stripe4_dhs) for observations meant to be taken in parallel with sw_tsgrism.
JETC-4273JWSTReference data files for MIRI, NIRCam, NIRISS, and NIRSpec have been updated to the latest on-orbit measurements.
JETC-4162JWSTnirspec ifu now supports the 4 point nod strategy. With this new strategy, "ifunpointnod", the "strategy" "dither" entry of the input dictionary is now a keyword (with "nod4" as the only option) rather than a list of dither positions. However, only nod 1 of the 4-point nod is actually visible in the output 2D images.
JETC-4278JWSTThe entire PSF library has been regenerated with WebbPSF 1.3 and POPPY 1.1.1, with the latest distortion and other detector effects included.
JETC-4387JWST, RomanA warning will be triggered if the aperture or sky region/annulus is smaller than a pixel.
JETC-4416JWST, RomanThe minimum supported Python version is now 3.9
JETC-3759JWST, RomanThe Pandeia Engine is compatible with numpy 2.0

Version 4 will be released for JWST only

Reference ChangesJETC-1821JWST RomanAnswers using analytic spectra may change at below the 1% level, because the exact wavelength values used have changed.Other changesJETC-1758RomanFix: A bug that increased the brightness of sources as seen through the Roman F062, F087, and F158 filters by 100x has been corrected

.

What support is available?

Questions about the Pandeia engine for Webb may be directed to the JWST help desk; for Roman, email help@stsci.edu with Roman and/or WFIRST in the subject line or body. However, due to the complexity of the engine, support will be limited and response times may be longer than for other tools.

We welcome comments and feature requests, and these will be considered along with other ETC work.

What is the Pandeia Engine?

The Pandeia engine uses a pixel-based 3-dimensional approach to perform calculations on small (typically a few arcseconds) 2-dimensional user-created astronomical scenes. It models both the spatial and the wavelength dimensions, using realistic point spread functions (produced using WebbPSF) for each instrument mode. It natively handles correlated read noise, inter-pixel capacitance, and saturation. Since the signal and noise are modeled for individual detector pixels, the ETC is able to replicate many of the steps that observers will perform when calibrating and reducing their JWST data. This simplifies interpretation of the extracted signal-to-noise ratio (SNR) calculated by the ETC.  

Info
While the Pandeia engine includes many effects not typically included in other ETCs, it is not an observation simulator. It does not simulate the full detector, nor does it include 2-dimensional effects such as distortion.

Details on the algorithms used to compute signal and noise on the detector and the strategies used to compute the extracted products can be found in Pontoppidan et al. 2016.