Proposal Tools

The tools to craft a JWST proposal include:

  • The Exposure Time Calculator (ETC): it calculates the detailed performance of the observatory by modeling astronomical scenes consisting of single or multiple point and extended sources. It offers full support for all of the JWST observing modes.
  • The Space Telescope Image and Spectroscopy Simulator (STIPS): it is used to simulate JWST observations of large astronomical fields.
  • The PSF Simulation Tool (WebbPSF): it is used to simulate detailed point spread functions for all the JWST instruments.
  • The JWST project has several Target Visibility Tools (including the General Target Visibility Tool, the Coronagraphic Visibility Tool, and the JWST Backgrounds Tool) to assess target visibilities.
  • The Astronomer’s Proposal Tool (APT): it is used to write, validate and submit proposals for both the Hubble Space Telescope and the James Webb Space Telescope.
  • A simulated data sets for NIRCam, NIRISS, NIRSpec, and MIRI

Pseudocolor image of the central region of a globular cluster viewed in the Z087, J129, and F184 filters of the WFIRST Wide Field Imager, as simulated using STIPS.

The STIPS (Space Telescope Image Product Simulator) software produces simulated imaging data for complex wide-area astronomical scenes, based on user inputs, instrument models and library catalogues for a range of stellar and/or galactic populations. It was originally developed for the JWST mission, but now has been extended to include WFIRST functionality as well. The current JWST version produces images covering the MIRI detector, either one or both NIRCam Long detectors, and either one, four, or all eight NIRCam Short detectors. STIPS includes the most current information about the telescope sensitivity, spectral elements, and detector properties; it uses the PSF model generated by WebbPSF for JWST, and it calls the appropriate Pandeia/JWST ETC modules to compute instrumental throughput and count rates. STIPS is based on a Python module and a web interface that provides a straightforward way of creating observation simulations. In its current implementation, it runs server-side and allows users to submit simulations and view/retrieve the results (More on STIPS).

The WebbPSF computes PSFs from a supplied library of optical path difference (OPD) files consistent with the JWST optical error budget, including wavefront errors in the Optical Telescope Element (OTE) and in each instrument. 10 independent statistical realizations are provided for each. Using these, WebbPSF computes observed PSFs assuming Fraunhofer (far-field) propagation. WebbPSF provides:

    • PSF simulations for direct imaging and coronagraphic modes, and for non-redundant aperture masking on NIRISS.
    • Improved instrument properties such as normalized filter throughputs for NIRCam, NIRspec, and NIRISS, and detector pixel scales and orientations for all instruments.
    • Arbitrary oversampling of output PSFs
    • Quick calculations using optimized matrix Fourier transforms, the fast semi-analytic coronagraphy algorithm, and the FFTW3 library (optional).
    • Built-in functions for PSF evaluation such as producing radial profile plots, measuring encircled energy curves, FWHMs, etc.
    • A greatly improved graphical user interface.
    • An easy-to-use scripting interface for integration with other tools.

Limitations: The spectroscopy modes of NIRSpec and MIRI are not yet supported. Detector imperfections are likewise not included. The current OPD models do not support field-dependent wavefront error across the instrument FOVs. Future versions of WebbPSF and related software packages will address these issues.

Simulated observations have been created for each of the instruments listed below as a way to familiarize investigators with JWST data products. These high fidelity simulations were developed by JWST instrument team members, including instrument scientists at STScI and ESA. Simulation data for MIRI and NIRSpec remains available through an FTP hosted by ESA. Data files that were used to generate the simulated observations, such as catalogs of sources, SEDs, background, etc., are also provided where available. Most data are organized and formatted in substantially the same way as they would from a genuine observing program for various observing modes. Data files may be retrieved individually or, in some cases, in bulk from the linked pages listed below:

  • MIRI data simulations (at ESA) include an Integral Field observation with the Medium Resolution Spectrograph (MRS), a Low Resolution Spectrograph (LRS) observation, and an imaging observation (voir MIRISim)
  • NIRCam data
  • NIRISS data simulations include the following science modes: Imaging, Wide-Field Slitless Spectroscopy (WFSS), Single Object Slitless Spectroscopy (SOSS) and Aperture-Masking Interferometry (AMI).
  • NIRSpec data simulations (at ESA) include observations using the Multi-Object Spectroscopy (MOS) mode and Integral Field Spectroscopy (IFU) mode.
  • Note: The format and organization of most of the data and metadata in the FITS files offered here is the same as that expected for Level-1b products.

    APT is an integrated toolset consisting of editors for filling out proposal information, an Orbit Planner for determining feasibility of the observations, a Visit Planner for determining schedulability, diagnostic and reporting tools, a Bright Object Tool for performing bright object checks, and eventually an integrated tool which will be based on Aladin for viewing exposure specifications overlaid on FITS images.

    An important tool when elaborating a proposal is the Field of Regard of the JWST: the Figure illustrates the great coverage of the telescope (more on the Coordinate System and Field of Regard).

    The JWST project provides two quick-look target visibility tools to help in pre-planning observations, and for determining their feasibility, prior to entering them in APT: the General Target Visibility Tool (GTVT) predicts visibility windows and position angles for all instruments (GTV), and the Coronagraphic Visibility Tool (CVT) provides target visibility information for the NIRCam and MIRI coronagraphic modes (CVT). The JWST APT Visit Planner (VP) includes other aspects of schedulability beyond just visibility, including the availability of guide stars at relevant position angles, and any special requirements levied on the observations in APT. APT is the final arbiter of schedulability.

    The APT version 25.4.3  and its associated documentation have been formally released on February 20, 2018 by the Space Telescope Science Institut (STScI). It can be downloaded from

    What’s New can be found here, and tutorials can be watched on Training Videos.

    Version 25.4.2 had to be used to support JWST Early Release Science (ERS) and Guaranteed Time Observers (GTO) (and also HST Cycle 25 Phase I) submissions. This version can also be used for GO observations, but users are recommended to use the 25.4.3 one.

    Version 1.2 of the JWST ETC has also been released on December 2017 ETC login. As a note, when you log in to the 1.2 ETC, your old workbooks will be marked « Out of Date »:

    • When you load them, they will open in Read-Only mode: this ensures that your previous results are not overwritten and remain available to you for reference.
    • If you copy an out of date workbook, and load the copy, all its calculations will be automatically updated for you with the current version of the software.
    • For more information, see ETC Releases and Out-of-Date Workbooks.

    In addition, JWST ETC version 1.2 features faster performance, accuracy improvements, usability enhancements, and more.

    Exemple of output from the ETC (here the signal-to-noise ratio).

    The version 1.2.2 of the ETC has been released on March 19, 2018. This patch includes accuracy-related changes for several modes, as well as critical performance and robustness improvements.

    Important Note: When you log in to the 1.2.2 ETC, your old workbooks will be marked « Out of Date »: they will open in Read-Only mode: this ensures that your previous results are not overwritten and remain available to you for reference. If you copy an out of date workbook, and load the copy, all its calculations will be automatically updated for you with the current version of the software.

    Accuracy Improvements:
  • Calculations now treat « number of exposures » as « number of dithers ». This correctly decreases the residual flat field error for dithered observations.
  • Major accuracy improvements have been achieved for NIRCam and MIRI Coronagraphy modes, MIRI Coronagraphic Target Acquisition, and NIRISS long-wavelength Imaging and TA modes, by using a redesigned and better-sampled PSF Library.
  • MIRI:

  • MIRI Four Quadrant Phase Masks now include the effect of the quadrant boundaries on off-centered PSFs.
  • The MIRI Lyot Coronagraphic Mask is now more appropriately sampled (positions of the pre-calculated PSFs).
  • MIRI Coronagraphic Target Acquisition no longer erroneously has the coronagraph stops in the pupil plane.
  • NIRCam:

  • NIRCam Coronagraphy bar masks are now more appropriately sampled (positions of the pre-calculated PSFs).

  • NIRISS Imaging in long-wavelength filters now include the pupil mask, leading to a ~16% reduction in flux. This affects the F277W filters and longer wavelengths, for Imaging and Target Acquisition modes.
  • New Features:
  • NIRSpec IFU and MIRI MRS modes now report saturations from both « Nod » positions independently.
  • Coronagraphy modes now report saturations from both Science Scene and PSF subtraction source separatedly.
  • The Coronagraphy Strategy has been enhanced by providing a total of four options under « PSF Subtraction ».
  • « Optimal (PSF Autoscaling) » will automatically scale the PSF subtraction source to the flux of the central source before subtraction. This matches the ETC 1.2 behavior for « Optimal » subtraction.
  • « Optimal (No PSF Autoscaling) » with no scaling of the PSF subtraction source. This matches the ETC 1.1.1 and earlier behavior for « Optimal » subtraction.
  • « Unsubtracted Science Scene » displays only the science scene, with only the coronagraphic mask suppressing the central source.
  • « PSF Subtraction Source only » displays the PSF subtraction source by itself, under the coronagraphic mask.
  • Under the hood:
  • ETC 1.2.2 is installed on more powerful hardware, to better support heavy load as the deadlines for proposal submissions approach.
  • Improvements have been made to database handling and resource management.
  • Additional logging and monitoring has been added to facilitate problem investigation.

    Note that the old workbooks from previous ETC versions are locked to facilitate comparisons..

  • When you load them, they will open in read-only mode. This ensures that your previous results are not overwritten and remain available to you for reference.
  • When you copy an out-of-date workbook and load the copy, all of its calculations will be automatically updated for you with the current version of the software.
  • See the Release Notes for details, and be sure to review the Known Issues for this release (and the previous ones).

    Several JWST community oriented products and tools had been launched at the January 2017 AAS meeting and provided the following links to the main elements:

    • JDOX:
    • ETC:
    • ERS CfP:
    • JWST Help Desk:
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