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 3.2 (JWST), 3.1 (Roman).

Next Planned Release

The next 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.

Version 3.2 is only for JWST and includes the following changes since 3.0:

JETC-1867JWST, RomanThe imagingapphot strategy can now optionally use "pixel" as the unit, in which case aperture_size defines the width of a square extraction box, and the sky_annulus defines the outer and hole regions of a square sky region with a square hole in it. 
JETC-3638RomanThe Pandeia engine now supports unevenly sampled MA tables. The new configuration-detector options are "ma_table_name", which must be the valid name of an MA Table;"nresultants", which must be an integer between the table's defined minimum number of allowed resultants and the maximum defined resultant number; "nexp", which continues to define the number of dithers/exposures of a given readout; and "subarray", for which the only current option is "full". 
JETC-1559JWST, RomanThe order in which Extinction and Normalization are applied to spectra can now be changed via a keyword, "extinction_first", in the spectra portion of the source definition. The default, true, is the original behavior.
JETC-4064JWST, RomanFlux through apertures smaller than a pixel (which is not recommended) were inaccurately measured.
JETC-4100JWSTNIRSpec spectroscopic SNR and extracted flux have been underestimated by up to 30%, this has been corrected.

Version 4 will be released for both missions and contain all of these changes plus additional functionality to be worked.

What support is available?

Questions about the Pandeia engine for Webb may be directed to the JWST help desk; for Roman, email 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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