Imaging Performance

MIRI, NIRISS, and NIRCam imaging have different sensitivity, saturation, and spatial resolution characteristics.


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Main articles: NIRCam Imaging, NIRISS Imaging, MIRI Imaging 

Imaging detector characteristics are summarized here, including sensitivity, saturation, and spatial resolution. See the instrument-specific pages for details (links below).



Imaging sensitivities

Main articles: NIRCam Imaging Sensitivity, NIRISS Sensitivity, MIRI Sensitivity
See also: NIRCam Detector Readout PatternsMIRI Detector Readout OverviewNIRISS Detector Readout PatternsJWST ETC

The sensitivity of each JWST imaging filter is summarized in Figure 1.  The JWST Exposure Time Calculator (ETC) was used to estimate the signal to noise (S/N), with readout patterns chosen to reach approximately 10 ks in each instrument and using a benchmark background, as described on the JWST Background Model article.  More details about each instrument's sensitivity can be found in the following articles:

Figure 1. JWST imaging sensitivity

The S/N = 10 detection limits of JWST's imaging instruments in 10 ks, shown for every available filter. The horizontal error bars represent the width of the filter. Sources are assumed to have a flat spectrum in nJy and a benchmark background, as described on the JWST Background Model article. Please use the JWST Exposure Time Calculator (ETC) to calculate sensitivity estimates for your specific proposed observations.


Imaging saturation limits

The bright source limits for each imaging mode (including time-series and high-contrast imaging) are found at the following articles:


Imaging spatial resolution

The FWHM of the point spread function (PSF) for each instrument can be found at the links listed below. The pixel scales for the images are 0.031″/pix for NIRCam's short wavelength channel, 0.063″/pix for NIRCam's long wavelength channel, 0.066″/pix for NIRISS, and 0.11″/pix for MIRI.  The NIRCam detectors achieve Nyquist sampling (FWHM > 2 pixels) at λ > 2 μm in the short wavelength channel and at λ > 3.4 μm in the long wavelength channel. NIRISS is Nyquist sampled at λ > 4 μm, and MIRI is Nyquist sampled for all filters except F560W. More information is available in these articles:


Table 1. Information on imaging spatial resolution


PSF FWHM

(pix)

Plate scaleNyquist sampled
NIRCam

0.987–2.341 (SW)

1.340–2.574 (LW)

0.031 (SW)

0.063 (LW)

>2 μm (SW)

>4 μm (LW)

NIRISS2 pix @ 3.4 μm0.066>3.4 μm 
MIRI1.00–7.450.11>6 μm 




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