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 1.7.

Next Planned Release

The next release of the Pandeia Engine will be after JWST commissioning.

The next release will require Python 3.8+, as a result of Astropy 5.0

In the next release:

Known IssuesMission
JETC-1957JWST, RomanThe engine accepts non-integer values for groups, integrations, and exposures , even though these are unphysical.
JETC-2093JWST RomanUsers can now specify "pixel" as an option for extraction units.
JETC-2109JWSTSetting a reference_wavelength to None will now choose a similar wavelength to the "Update to Midpoint" button in the web interface
JETC-2354JWST Roman

New normalization bandpasses: johnson_u, johnson_b, johnson_r, cousins_r, galex_fuv, galex_nuv. None of the new normalization bandpasses are within the wavelength range of JWST. 

JETC-2358JWST RomanThe next release will not support versions of Python older than 3.8

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.  

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.

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