MIRI Sensitivity

The sensitivity model for JWST's Mid-Infrared Instrument (MIRI) incorporates ground testing measurements to model parameters such as background, photon conversion efficiency, encircled energy, and detector performance.

JWST sensitivity update

Preliminary results from observatory commissioning indicate that system throughput is higher than pre-mission expectations, by amounts that vary with wavelength. Until detailed results are available and updated in Pandeia, results calculated by the ETC and JIST tools will underestimate S/N. An announcement will be made when the tools are updated.

On this page

The performance of JWST has been measured directly at both the component and system level using the fully assembled MIRI flight model in a flight-like radiative environment with a well-characterized radiometric source (Glasse et al. 2015). The results of the JWST throughput measurements have been integrated into a sensitivity model that includes the following components: (1) background, (2) photon conversion efficiency (PCE), (3) encircled energy, and (4) detector performance (Pontoppidan 2016).

Users should ultimately use the Exposure Time Calculator (ETC) for all sensitivity calculations.

The values in the table and plots below were obtained from ETC 1.5.1.


The tables and figures below show point source sensitivity values for a 10 ksec (10,000 s) observation to S/N = 10.

Table 1. Minimum detectable flux densities for a S/N = 10 in 10 ksec for MIRI imaging filters assuming FULL array, assuming an unresolved point source.

FilterLow Background Detection
Limit (μJy)

Figure 1. Expected point source sensitivity for the various MIRI instrument modes

MIRI point source sensitivity plot for the medium-resolution spectrometer (MRS), low-resolution spectrometer (LRS), and imager (in circles) configurations. Values plotted represent the minimum detectable signal  corresponding to S/N = 10,  in 10,000 seconds on-source integration time. For spectroscopic modes the numbers represent continuum sensitivities, with S/N calculated per spectral pixel.


Glasse, A., et al., 2015, PASP, 127, 686 
The Mid-Infrared Instrument for the James Webb Space Telescope, IX: Predicted Sensitivity

Pontoppidan, K. 2016, Proc of SPIE, 9910, 16
Pandeia: a multi-mission exposure time calculator for JWST and WFIRST 

Latest updates

  • Updated plots and tables with values from ETCv1.5.1

    Updated plots with values from ETCv1.5

  • Updated Sensitivity graph to reflect current values used

  • Updated Imager sensitivity table to reflect currently used values in ETC.
Originally published