NIRISS Imaging APT Template

Instructions for filling out the JWST NIRISS imaging template, using the Astronomers' Proposal Tool (APT), are provided in this article.

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See also: NIRISS Imaging, JWST Parallel Observations, NIRISS Imaging Recommended Strategies, APT Coordinated Parallel Observations

Imaging is one of 4 modes on the Near Infrared Imager and Slitless Spectrograph (NIRISS), offering image capability over the wavelength range from 0.8 to 5.0 μm. This mode is offered as a prime observing mode and as a coordinated parallel observing mode when NIRCam imaging or NIRCam wide field slitless spectroscopy (WFSS) is used as the prime science mode. 

The user will have control over the following parameters: (1) Dithers, (2) Filters, and (2) Readout Pattern and exposure time (via Groups/Int and Integrations/Exp). 

Step-by-step APT instructions are provided below.

Generic parameters

Words in bold are GUI menus/
panels or data software packages; 
bold italics are buttons in GUI
tools or package parameters.

The following parameters are generic to all templates, and are not discussed in this article: observation Number, observation Labelobservations CommentsTarget name, ETC Wkbk. Calc ID (in the Filters dialog box), Mosaic Properties, and Special Requirements.

NIRISS Imaging tab


Choose the NIRISS imaging dither pattern. The dither offsets are large enough to ensure that a compact source does not fall on the same pixel twice, but not so large as to be affected by distortion across the detector.


  • Image Dithers: number of steps, where the first step corresponds to initial pointing; allowed values are 2, 3, 4, 6, 8, 12, 16
  • Pattern Size: amplitude of dither step; allowed values are SMALL (≈0.3"), MEDIUM (≈0.6")and LARGE (≈1.2")


See also: NIRISS FiltersNIRISS Detector Readout PatternsUnderstanding JWST Exposure Times


  • FiltersF090W, F115W, F140M, F150W, F158M, F200W, F277W, F356W, F380M, F430M, F444W, F480M 
  • Readout Pattern
    • NISRAPID: all frames are read and stored. Generally this can be used if the number of frames per integration is small and data volume is not an issue. There is a limit of 30 on the number of groups per ramp in the NISRAPID read out, though a limit of 25 is recommended to mitigate the effects of cosmic ray hits.
    • NIS: four frames are averaged per group. Used for producing a lower data rate for longer integrations of faint targets. 
  • Groups/Intthe number of groups during an integration, equal to the number of frames read per integration (for NISRAPID), or the number of frames read out divided by 4 (for NIS).
  • Integrations/Expthe number of integrations during an exposure, where an integration is the time between detector resets. 
  • ETC Wkbk. Calc ID: the accompanying ETC workbook ID number for the calculation (optional).

The Exposure Time Calculator (ETC) should be used to determine the combination of Groups/Int and Integrations/Exp necessary to achieve the required signal-to-noise ratio. Individual integrations longer than 1,000 s are discouraged because of the effect of cosmic ray hits on the detector. For long exposures, a suitable number of integrations and a number of groups less than or equal to 25 is suggested.

Latest updates
    Updated to support imaging as a prime observing mode.

    Updated parameter headings to be consistent with APT v. 27.0

    Removed note that though subarray options are offered in the APT template, only full-frame readout is supported in imaging mode. As of APT v. 26.1, subarray options are no longer offered in the NIRISS imaging template.
Originally published