The algorithms for CALWEBB_AMI3, the 3rd stage of the JWST calibration pipeline for NIRISS Aperture Masking Interferometry (AMI), are described. These algorithms process the data from calibrated slope images to fringe parameters.
The CALWEBB_AMI3 module is the 3rd stage in the calibration pipeline for the NIRISS Aperture Masking Interferometry (AMI) data. The inputs to this stage are the calibrated slope images (CALWEBB_IMAGE2 output) and the output is fringe parameters. The steps are listed in Figure 1 with the flow from the top to the bottom.
Unless otherwise stated, the algorithms described are the baseline version.
See also: AMI Processing (more detailed software module documentation)
Assemble reference PSFs
The available list of reference PSFs is generated. These reference PSFs consist of reference stars specifically observed for the target.
Calculate fringe parameters
The closure phases and visibilities for each reference PSF and target are calculated. As part of this calculation, the centers of the reference and target PSFs are determined (iteratively).
Average fringe parameters
Averaging the fringe parameters taken over multiple exposures improves the signal-to-noise of the measurements. The averaging is done for both the target and reference PSF observations.
Final fringe parameters
The reference PSF closure phases are subtracted from the target closure phases. The target visibilities are divided by the reference PSF visibilities. These two calculations are done matched by dither position.