NIRISS Detector Overview

The JWST NIRISS instrument is equipped with a Hawaii-2RG detector, a single 2048 × 2048 pixel sensor chip array (SCA), providing a 2.2′ × 2.2′ field of view. It has an average pixel scale of 0.066"/pixel

Manufactured by Teledyne Imaging Sensors, the NIRISS detector is made of HgCdTe with a specific composition tuned to provide a wavelength cutoff at approximately 5 μm. Detector readout is controlled by a SIDECAR (System for Image Digitization, Enhancement, Control, and Retrieval) ASIC (Application Specific Integrated Circuit) that sets the bias voltages and performs the analog-to-digital conversion of the pixel voltages.

The detector has a 4-pixel wide border of reference pixels which do not respond to light, but are sampled and digitized in the same way as the photosensitive pixels. These reference pixels can be used to monitor and remove low frequency bias drifts on a frame-to-frame basis. The full array of sensitive pixels is 2040 × 2040.

The pixel size of the NIRISS detector is 18 × 18 μm which offers an average plate scale of 0.0653"/pixel × 0.0658"/pixel which varies slightly across the detector and from filter to filter. The full well capacity of the detector is approximately 105 e. Properties of the NIRISS detector are summarized in Table 1. A photo of the detector is shown in Figure 1.

Further information about the NIRISS detector properties that are important to consider when planning science observations can be found at the following articles:

Table 1. NIRISS detector properties


SCA size

2048 × 2048 pixels

Pixel size

18 × 18 μm (physical)

Plate scale in X1


Plate scale in Y1


Full well capacity

95,000 to 105,000 e

Quantum efficiency

0.88 from 0.5 μm - 5 μm

Read noise (correlated double sampling)

16.8 e-

Dark signal @ 39K

0.5154 e-/frame


1.61 e/ADU

Reported plate scales are the average value. There is a slight dispersion in plate scale across the detector and from filter-to-filter.

Figure 1. NIRISS HgCdTe detector

© Teledyne Imaging Sensors


Doyon, R. et al., 2012, Proceedings of the SPIE, Vol 8442
The JWST Fine Guidance Sensor (FGS) and Near-Infrared Imager and Slitless Spectrograph (NIRISS)

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    Updated with in-flight performance values
Originally published