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). Subarrays are not supported by the NIRISS imaging mode.
Step-by-step APT instructions
|PageWithExcerpt||MIRI Imaging Template APT Guide|
Main Article: NIRISS Filters
See Also: NIRISS Detector Readout Patterns
- 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 coadded per group. Used for producing a lower data rate for longer integrations of faint targets. For NIRISS imaging, the number of groups per integration should be 25 or less (even though APT nominally allows values up to 400) to avoid issues with cosmic ray hits.
- 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 should be selected.