Roman I-Sim - The Roman Image Simulator
The Roman image simulator, or Roman I-Sim , is a Python wrapper of GalSim (Rowe et al. 2015) that has been specifically designed around Roman's Wide Field Instrument (WFI) specifications. Roman I-Sim makes use of the official calibration reference files stored in the Roman Calibration Reference Data System (CRDS) and of WebbPSF point-spread function models to simulate realistic Level-1 (L1) and Level-2 (L2) WFI data products in imaging mode.
Roman I-Sim in a Nutshell
Roman I-Sim can simulate all 18 Sensor Chip Assemblies (SCAs) through all available imaging optical elements. Simulations take advantage of GalSim to precisely render scenes (see the GalSim Documentation for more information), as well as of Roman-specific multi-accumulation tables, to generate uncalibrated resultants (L1) or the corresponding calibrated rate images (L2) as ASDF data products.
Roman I-Sim is the recommended Roman image simulator for high-fidelity, realistic WFI L1 and L2 data products in imaging mode.
Figure of Roman I-Sim Full-frame Galaxy Field
A full-frame view of a level-2 simulated image of a galaxy field is shown on the left as seen through filter F158, made as a collage of 18 individual runs of Roman I-Sim on the 18 SCAs. The encircled region (radius = 500 pixels or 55 arcsec) in SCA 12 is zoomed in and shown on the right. The full white/black dots are bad pixels as marked in the data quality (DQ) array calibration reference file.
Current Version
This documentation is written for Roman I-Sim version 0.7.0 (released on December 6, 2024). The software package can be obtained from the STScI Roman I-Sim Github repository. Up-to-date development documentation of Roman I-Sim and of its methods and functions is available in the Roman I-Sim readthedocs.
When to use Roman I-Sim
Compared to other SOC simulation tools like Pandeia or STIPS , Roman I-Sim is best suited for high-fidelity data products over SCA-size field of views. The software package is able to account for realistic detector effects and noise sources through its read-by-read uncalibrated image generation and the corresponding up-the-ramp calibrated rate output. Roman I-Sim offers comparable results to Pandeia in terms of realism of the simulation, but over much larger field of views. Moreover, the Roman I-Sim outputs are the only simulated products that conform to the Roman datamodel and are suitable for further processing with the STScI Roman pipelines. Roman I-Sim is more CPU demanding than STIPS but it offers a much higher level of fidelity, especially in terms of realistic noise and detector properties.
Acknowledgements
Roman I-Sim is written and maintained by the Roman Science Operations Center (SOC) at STScI.
For additional questions not answered in this article, please contact the Roman Help Desk at STScI.
References
- Rowe, B. T. P., Jarvis, M., Mandelbaum, R., et al. 2015, Astronomy and Computing, 10, 121. doi:10.1016/j.ascom.2015.02.002
- Roman I-Sim on readthedocs: https://romanisim.readthedocs.io/en/latest/
- Roman I-Sim github repository: https://github.com/spacetelescope/romanisim