Improved model for MIRI cruciform artifact, part 1

[mperrin]

Summary:

This PR implements an improved model for the cruciform artifact seen in MIRI, in particular modeling the shifts of the cruciform lines as a function of position. This is motivated by comparisons with actual MIRI ePSFs by Libralato et al. 2024.

The key changes are

• switching from applying 2 x 1D convolution kernels to applying a single 2D convolution kernel
• Implementing a simple linear parameterization for shifts of the X and Y bright lines, derived from measured MIRI ePSFs in F560W.

Example plots showing the outputs and comparing to data are included below.

This is intended as the first PR of at least two for improving the MIRI ePSFs (broken up for complexity and to keep the reviews more manageable / bite-sized). A next step would add in models for the 'peaks' in the cruciform, as predicted by Gaspar et al, and as observed in MIRI LRS ePSFs.

A few additional pieces

There's also a little helper function for displaying the cruciform models, which is not used in calculations but helps visualize what's going on:

As you can see in the above, this PR also adds a model for the diffuse radial halo part of the "cruciform". See Figure 12 of Gaspar et al. 2021. This is a small but nonzero portion of the cruciform physics which we previously have neglected; this portion of the model is harder to base in empirical data given SNR of available ePSFs, but it seems

Example outputs and comparisons with data

Comparisons: F560W

• Data: miri_epsfs_F560W_measured.pdf
• Without this PR (current webbpsf): miri_epsfs_F560W_sim_released.pdf
• With this PR: miri_epsfs_F560W_sim_new.pdf

Comparisons: F770W

• Data: miri_epsfs_F770W_measured.pdf
• Without this PR: miri_epsfs_F770W_sim_released.pdf_
• With this PR: miri_epsfs_F770W_sim_new.pdf

[pep8speaks]

Hello @mperrin, Thank you for updating !

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Comment last updated at 2024-05-17 14:57:33 UTC

[mperrin]

FYI to @merope82 and @mlibralato - here's an update to improve cruciform artifact models in webbpsf.

[obi-wan76]

This looks good to me. I did a comparison at different wavelengths with some PSF subtraction and, even close to the center of the detector, there is a better residual at lower wavelengths.