All JWST detectors integrate using the MULTIACCUM readout, which consists of up-the-ramp sampling that utilizes a combination frames, groups, integrations, and exposures to arrive at a total exposure time.
How MULTIACCUM readouts Work
The MULTIACCUM readout is the standardized readout sampling for all JWST detectors. In MULTIACCUM readout, the array is read out non-destructively at intervals defined by the parameters described below during the exposure. Multiple non-destructive "frames" can be averaged by the onboard flight software into a "group" and transferred to the solid state recorder for downlinking to the ground. The ground-based data processing software can then correct bias drifts using the reference pixels and use “up-the-ramp” processing algorithms to reject cosmic rays. The MULTIACCUM approach is quite flexible since it allows for a large range of readout patterns, while permitting teams to subselect a relatively small set of optimal patterns for observations in flight. Figure 1 illustrates the components of each MULTIACCUM exposure:
For MIRI, users will have some degree of freedom in choosing these parameters. For NIRSpec, NIRCam, and NIRISS, users will select a patterns from a menu of available exposure options that are optimized for different types of targets.
Ressler, M. E. et al. 2015, PASP, 127, 675