The JWST Exposure Time Calculator (ETC) calculates the signal to noise ratio for NIRCam Imaging mode, allowing users to determine the observing parameters required for their science goals.

NIRCam observes the same 9.7 square arcminute field of view simultaneously in a short-wavelength channel (0.6–2.3 µm) and a long-wavelength channel (2.4–5.0 µm) via a beam splitting dichroic. Twenty-nine NIRCam filters are available for imaging. One filter is selected for each wavelength channel and images with both channels are made simultaneously.

NIRCam Imaging in APT and ETC 

In the APT, there is one NIRCam Imaging template available, which includes both the short-wavelength (Short Filter) and long-wavelength (Long Filter) detector setups in the same observation specification line (see upper panel of Figure 1). In the ETC, these are split into two separate calculations: SW Imaging and LW Imaging (see lower panel of Figure 1). These two calculations must be selected separately from the NIRCam drop down list and there is currently no way to connect the two observations to each other. Users therefore need to be careful that the same Detector Setup parameters are specified for the SW Imaging and LW Imaging calculations in ETC because these values are only specified once in the APT for each filter combination.

To determine the optimal readout patterns, appropriate dither coverage and other observing strategies, please visit the NIRCam Observing Strategies page. For further information when comparing the APT to the ETC, visit the JWST ETC and APT Interface Support page.

Figure 1. APT and ETC comparison for the NIRCam Imaging mode

Top. Specifying a NIRCam Imaging observation in the APT. After selecting the NIRCam Imaging template, the user specifies both a Short Filter and a Long Filter from the respective drop down lists. Other parameters (Subarray, Readout Pattern, Groups/Int, Integrations/Exp) match with those in the ETC image below. Bottom. Specifying NIRCam SW Imaging and NIRCam LW Imaging in the ETC. These calculations must be selected from the NIRCam dropdown menu separately, even though the observations will be made simultaneously by NIRCam and are specified in the same line in the APT.



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