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 1.5.2.
- Get the latest engine release software, installable with pip
- See the installation instructions (or these Webb-specific ones)
- Get the optional data files that support certain target spectra manipulations
- Get the required mission-specific items:
| Webb | Roman |
|---|---|
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Next Planned Release
The next planned release is 1.6, expected in March 2021.
The following changes are expected to be included:
| Ticket | Mission | Release Note | Known Issue |
| JETC-1488 | All | Accuracy: Thermal, zodiacal, stray light, and (extra-)galactic background flux is now correctly sampled for all calculations. The effect will be most prominent with very-low-resolution input spectra, around the wavelengths of prominent galactic emission features. It will not affect overall background flux. | |
| JETC-626 | All | Bug fix: The temperatures, and therefore spectra, of the g2v and g5v phoenix model SEDs used to be the same (5750K); they are now 5800K (g2v) and 5700K (g5v). | |
| JETC-365 | JWST | New Mode: NIRSpec Bright Object Time Series (nirspec bots). The NIRSpec fixed_slit mode has been separated into two modes in order to provide accurate signal-to-noise estimates for NIRSpec time series observations. bots calculations do not include flat field noise and will thus report slightly higher SNR. Calculations using bots mode can only use the s1600a1 aperture and its specific subarrays; fixed_slit can no longer use the bots-only sub512s subarray | |
| JETC-1471 | JWST | Accuracy: Exposure times for NIRCam Grism Time Series (nircam ssgrism) noutputs=1 subarrays have been updated and should now match APT exactly. SNR values may increase by up to 1.5%. | |
| JETC-716 | JWST | New: The Pandeia Engine now supports use of the f277w filter in niriss soss mode. Use without the f277w filter now requires the 'clear' filter, rather than None. | |
| JETC-1470 | JWST | New: the nircam fullp subarray is now available for NIRCam imaging modes, for consistency with APT templates. | |
| JETC-1375 | JWST | New Mode: MIRI Imaging Time Series Observations (imaging_ts). It is similar to miri imaging, but like other time series modes flat field noise has been disabled, and SNR will be higher than miri imaging. |
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.
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.
