NIRISS Detector Subarrays

JWST NIRISS detector subarrays are designed to support imaging and spectroscopy observations of targets with a wide range of brightnesses. Smaller subarrays are configured to avoid the risk of saturation and offer high time resolution for bright target observations.

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See also: NIRISS Detector Readout

NIRISS offers 4 observing modes, including imaging and spectroscopy, that enables a variety of science observations (e.g., exoplanet transits, high redshift galaxies, high resolution imaging of stellar sources, AGNs, etc.). The NIRISS detector is configured for full frame and subarray readout to enable observations of science targets with a wide range in brightnesses. 

Full frame readout

In full frame readout, the entire NIRISS detector array is read out through 4 parallel output channels, each reading a 512 × 2048 pixel region with its own readout amplifier. Full frame readout is the only supported readout for the NIRISS WFSS and NIRSS imaging observing modes.

Subarray readout

See also: NIRISS Bright Limits

NIRISS detector subarrays are read out faster and permit shorter integration times, thereby extending the dynamic range of NIRISS to bright sources. Subarrays also enable observations at high cadence which is particularly useful for science targets that require high time resolution (e.g., exoplanet transits, eclipsing binaries). All subarrays use single channel readout. The subarrays are essential for the NIRISS SOSS and NIRISS AMI modes.

The frame time for a subarray depends on the size of the subarray. The frame times for the SOSS and AMI observing and target acquisition modes are summarized in Tables 1 and 2, respectively. The subarray sizes are given in (x,y) detector coordinates, where x is the slow read direction and y is the fast read direction. Both observing modes can also be observed with full frame readout.

Single object slitless spectroscopy (SOSS)

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panels & data software packages.

See also: NIRISS Single Object Slitless Spectroscopy, NIRISS Target Acquisition

Table 1. Available NIRISS SOSS subarray modes

Subarray ID

Subarray size

Frame time



2048 × 96


SOSS for bright targets
Samples only 1st order


2048 × 256


SOSS mode default
Samples orders 1–3


64 × 64


SOSS target acquisition

Aperture masking interferometry (AMI)

See also: NIRISS Aperture Masking Interferometry, NIRISS Target Acquisition

Table 2. Available NIRISS AMI subarray modes

Subarray ID

Subarray size

Frame time



80 × 80


AMI mode for bright targets


64 × 64


AMI target acquisition

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