This article provides instructions for filling out the JWST NIRISS imaging template.
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 currently supported to be used in parallel when NIRCam Imaging is used as the prime science mode. Other prime+parallel combinations involving NIRISS imaging in parallel will be considered for implementation in Cycle 2.
The user will have control over the following parameters: 1) filters, and 2) read-out pattern and exposure time (via number of groups and integrations). Note: though the NIRISS Imaging APT template currently offers subarray options, only full-frame readout is supported by the NIRISS imaging mode. The subarray options will be removed in a future APT release.
Step-by-step APT instructions
- FILTER: F090W, 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 NISRAPID read out.
- NIS: four frames are averaged per group. Used for producing a lower data rate for longer integrations of faint targets.
- NO. OF GROUPS: the 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).
- NO. OF INTEGRATIONS: the number of integrations during an exposure, where an integration is the time between detector resets.
The Exposure Time Calculator (ETC) should be used to determine the combination of NO. OF GROUPS and NO. OF INTEGRATIONS necessary to achieve the required signal-to-noise. Individual integrations longer than 1000 seconds 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.