JWST ETC Strategies

The JWST Exposure Time Calculator (ETC) reports the results of calculations performed using a specified strategy that includes information about location and size of the extraction aperture, wavelength of interest, and choice of regions for background subtraction.

The JWST ETC enables exposure time calculations for a variety of instrument modes, including direct imaging, slit spectroscopy, slitless spectroscopy, integral field unit (IFU) spectroscopy, and coronagraphic imaging. The signal-to-noise ratio is computed using extraction strategies that are specific to the different modes. After the user has selected the scene, backgrounds, instrument setup, and detector setup, as described in the article Creating a JWST ETC Calculation, the next step is to define the strategy to be used for computing the signal-to-noise. The Strategy* tab, shown below, provides choices for the extraction strategy, background subtraction, size and position of the background region, and the wavelength of interest/slice for spectroscopic calculations.

Figure 1. Location of the strategy tab in the ETC web application

The strategies are set using the Strategy tab on the Calculations tab page.

* Bold italics style indicates words that are also parameters or buttons in software tools (like the APT and ETC). Similarly, a bold style represents menu items and panels.

List of articles

  1. JWST ETC Imaging Aperture Photometry Strategy: Information on the strategy used for MIRI, NIRCam, and NIRISS imaging calculations, as well as NIRSpec IFU Verification Imaging calculations.
  2. JWST ETC Aperture Spectral Extraction Strategy: Details of the extraction strategy available for slitted mode calculations, such as MIRI LRS Slit and NIRSpec Fixed Slit.
  3. JWST ETC MSA Full Shutter Extraction Strategy: Information specific to the extraction strategy for NIRSpec MSA calculations.
  4. JWST ETC IFU Nod In Scene and IFU Nod Off Scene Strategy: A description of the two strategies available for MIRI MRS and NIRSpec IFU calculations.
  5. JWST ETC SOSS Spectral Extraction Strategy: Specific information on the extraction strategy for NIRISS SOSS calculations.
  6. JWST ETC Coronagraphy Strategy: Information on the strategy used for MIRI and NIRCam coronagraphic imaging calculations.
  7. JWST ETC MSA Aperture Photometry Strategy: Details on the extraction strategy for the NIRSpec MOS Verification Imaging mode.
  8. JWST ETC MSA Shutter Photometry Strategy: Details on the extraction strategy for the NIRSpec MOS Confirmation Imaging mode.

For additional instrument/mode specific ETC strategies please refer to NIRISS AMI Recommended Strategies, NIRISS Imaging Recommended Strategies and  NIRISS WFSS Recommended Strategies articles.

Latest updates

  • Updated for ETC v1.5.

  • Updated for ETC v1.3.
Originally published