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MIRISim is provided on a best-effort basis, and intended to allow MIRI users to gain experience with the data produced by the instrument, how MIRI data are reduced by the JWST Pipeline, and help with observation feasibility studies. It is not a sensitivity calculator, and users planning observations are required to use the JWST Exposure Time Calculator (ETC). See the JWST Observation Planning page for more information about JWST planning tools.

Installation Instructions

MIRISim is released 'as is' as part of the MIRISim - MIRICLE data analysis package, available on the MIRISim Software Installation page. More details can be found in the user guide linked below.

MIRISim Mailing List

To receive updates on MIRISim releases, please sign up to our mailing list at the following page:

When signing up (by clicking the link above), your browser will likely warn you that 'This connection is not private'. You will be sent an email request to confirm your subscription. The only personal information we request is your name and email address (to send emails to). The mailing list is moderated: only moderators can send emails to the list. Announcements are expected to be in-frequent.

Release Notes, Guide Notebooks & Known Issues

The current release is 2.4.0, and the release notes, known issues, and Jupyter notebooks with guides can be found here

Major releases (e.g. 1.1.0 or 2.0.0) will be announced via the mailing list, minor updates (e.g. patch releases, 1.0.1) will not be announced.

User Guide

The MIRISim user guide is available in PDF format on the 2.4.0 release page.

Example Setups

Presented below are a number of Jupyter Notebooks designed to help understand how to create MIRI simulations with MIRISim:

These Jupyter notebooks create scenes and do simple simulations for each othe light paths through MIRISim. These notebooks must be started from a terminal which is in the mirisim anaconda environment. These Jupyter notebooks are provided to help understand how to setup a scene for MIRISim, whether in an input file (e.g. scene.ini), or interactively in python.
  • Inputs_to_SkySim.ipynb gives a listing of all possible target types, and how to specify the groupings of parameters required for the spatial or spectral definitions
  • Make_FITScube_from_scene.ipynb gives an example of how to create a scene with a galaxy, and output it to a fits file
  • Creating_a_scene.ipynb shows how to create a specified scene in both .ini formatting, and inside python

Data Format

MIRIsim generates data files which emulate uncalibrated JWST exposures, otherwise known as "level 1b ramp data" (the file formats are described in the JWST documentation). Each 4-D level 1b FITS file includes the following FITS extensions:
  • Primary extension - FITS header only
  • SCI extension - detector data, with axes
    • Detector column
    • Detector row
    • Frame number (sampled up the ramp)
    • Integration number
  • PIXELDQ extension - data quality of pixel data, with axes
    • Detector column
    • Detector row
The PIXELDQ extension does not exist in genuine raw JWST data, but is used by MIRISim to flag known bad pixels and non-science areas of the detector.

More in-depth information about the miri data models can be found here in the miri datamodels pdf, while more information about generalised miri tools can be found here in the miri tools pdf.

Reporting Bugs

The MIRI team does not have a help desk, and is provided on a best-effort, 'as-is' basis. However if there are bugs in the MIRISim code, please email them to We don't promise to respond to all emails, but will take reported bugs into consideration in the MIRISim development plan. Answers to frequently asked questions may be found below.

Frequently Asked Questions

  • Which light paths does MIRISim simulate?
    • The Low Resolution Spectrograph (LRS), Medium Resolution Spectrograph (MRS) and Imgager main field. MIRISim does not simulate Coronographic observations
  • What is the ASDF extension contained in the output file?
    • This extension is managed by the JWST software and contains information which cannot easily be saved in pure FITS format. In the MIRISim case, the ASDF extension contains a copy of the world coordinates information already contained in the FITS header. The ASDF extension will be used by the JWST pipeline software. See the JWST documentation for more information on the data format.
  • How do I setup a target with an SED from pysynphot family XYZ?

MIRISim Development Plan

An non-exhaustive list of the MIRISim development plan includes bug fixes along with:
  • Incorporating updated MIRI team calibration data products (CDPs) as they become available.

MIRISim Developers

MIRISim is being developed by the MIRI European Consortium, with significant contributors at the UK Astronomy Technology Center (UK ATC); CEA Service d\x92Astrophysique, Saclay, France; Dublin Institute for Advanced Studies (DIAS); and the Max Planck Institute fur Astronomie (MPIA).

The miri software tools have been developed by the MIRI EC team as part of the JWST/MIRI consortium, which includes the following organisations: Ames Research Center, USA; Netherlands Foundation for Research in Astronomy; CEA Service d\x92Astrophysique, Saclay, France; Centre Spatial de Liege, Belgium; Consejo Superior de Investigacones Cientificas, Spain; Danish Space Research Institute; Dublin Institute for Advanced Studies, Ireland; EADS Astrium, Ltd., European Space Agency, Netherlands; UK; Institute d\x92Astrophysique Spatiale, France; Instituto Nacional de Tecnica Aerospacial, Spain; Institute of Astronomy, Zurich, Switzerland; Jet Propulsion Laboratory, USA; Laboratoire d\x92Astrophysique de Marseille (LAM), France; Lockheed Advanced Technology Center, USA; Max-Planck-Insitut fur Astronomie (MPIA), Heidelberg, Germany; Observatoire de Paris, France; Observatory of Geneva, Switzerland; Paul Scherrer Institut, Switzerland; Physikalishes Institut, Bern, Switzerland; Raytheon Vision Systems, USA; Rutherford Appleton Laboratory (RAL), UK; Space Telescope Science Institute, USA; Toegepast Natuurwetenschappelijk Onderzoek (TNOTPD), Netherlands; UK Astronomy Technology Centre (UKATC); University College, London, UK; University of Amsterdam, Netherlands; University of Arizona, USA; University of Cardiff, UK; University of Cologne, Germany; University of Groningen, Netherlands; University of Leicester, UK; University of Leiden, Netherlands; University of Leuven, Belgium; University of Stockholm, Sweden, Utah State University USA.
Topic attachments
I Attachment Action Size Date Who Comment
Creating_a_scene.ipynbipynb Creating_a_scene.ipynb manage 12 K 08 Oct 2020 - 15:28 PamelaKlaassen Scene Generation (python 3)
Galaxy_example_make_skycube.ipynbipynb Galaxy_example_make_skycube.ipynb manage 10 K 02 Feb 2018 - 17:32 PamelaKlaassen Create a FITS cube from SkySim?
Inputs_to_SkySim.ipynbipynb Inputs_to_SkySim.ipynb manage 34 K 08 Oct 2020 - 15:28 PamelaKlaassen SkySim? Inputs (python 3)
MIRISim.pdfpdf MIRISim.pdf manage 2 MB 25 Oct 2018 - 07:42 PamelaKlaassen MIRISim User Guide
MIRISim_IMA_walkthrough.ipynbipynb MIRISim_IMA_walkthrough.ipynb manage 75 K 08 Oct 2020 - 15:27 PamelaKlaassen Imager Walkthrough
MIRISim_LRS-slit_walkthrough.ipynbipynb MIRISim_LRS-slit_walkthrough.ipynb manage 83 K 08 Oct 2020 - 15:28 PamelaKlaassen LRS (Slit) Walkthrough
MIRISim_LRS-slitless_walkthrough.ipynbipynb MIRISim_LRS-slitless_walkthrough.ipynb manage 65 K 08 Oct 2020 - 15:29 PamelaKlaassen LRS (Slitless) walkthrough
MIRISim_MRS_walkthrough.ipynbipynb MIRISim_MRS_walkthrough.ipynb manage 115 K 08 Oct 2020 - 15:29 PamelaKlaassen MRS walkthrough
Make_FITScube_from_scene.ipynbipynb Make_FITScube_from_scene.ipynb manage 9 K 15 Nov 2018 - 08:41 PamelaKlaassen Make a FITS cube from a Scene (Python 3)
miri_datamodels.pdfpdf miri_datamodels.pdf manage 388 K 29 Oct 2018 - 10:51 StevenBeard MIRI_datamodels (29 October 2018)
miri_tools.pdfpdf miri_tools.pdf manage 152 K 29 Oct 2018 - 10:51 StevenBeard miri_tools (29 October 2018)
Topic revision: r4 - 01 Apr 2021, VincentGeers
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