JWST ETC Target Acquisition Strategy

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The JWST Exposure Time Calculator (ETC) calculates the signal-to-noise ratio (SNR) for target acquisition (TA) modes of all JWST instruments using the unique Target Acquisition strategy. The user specifies only the source, with all other parameters fixed due to the nature of TA calculations.

Words in bold are GUI menus/
panels or data software packages; 
bold italics are buttons in GUI
tools or package parameters.

 The following parameter is provided for Target Acquisition:

Aperture centered on source: The user has the option to choose which source in the scene to use for the TA calculation.

No other editable parameters are presented to the user on the Strategy tab due to the nature of TA calculations. The same process is used to compute the SNR for TA calculations with all instruments, which involves computing 2 "difference images," one between the first group and the middle group and the other between the middle group and the last group of the integration ramp. The Instrument Setup tab presents more editable parameters for TA calculations with MIRI, NIRCam, NIRISS, and NIRSpec.

Figure 1. Layout of the strategy tab for ETC target acquisition calculations

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