Improvements in MIRI LRS instrument model

[mperrin]

Digging into MIRI LRS for some science, I'm finding parts of the LRS mode model in webbpsf that can be improved / fixed

• Pupil stop is correctly set to the oversized tricontagon for the P750L pupil mask, but ought to be set to that for any imaging filter used with the LRS. (or, strictly speaking, in general, but we don't model the effects of the oversized internal pupil stop for regular imaging mode).

• The SI WFE model and the coordinate rotation appear to be in the wrong order in the optical system. The SI WFE model is in the detector frame, so should be after the rotation. This is true in regular imaging calcs, but for some reason is not true for LRS calcs.

• Need to update pupil shear for this mode using the values from commissioning. See Wright, Sabatke, and Telfer 2022

• Need to understand/double check relative about filter-dependent apparent offsets and how to account for them. In discussion with @skendrew . This may be outside of the scope of webbpsf but relevant for fitting physically-optics-based forward models to data for complex scenes seen via the LRS.

• Wavelength-dependent continuous version of the cruciform convolution kernel needed

• SI field dependent WFE: can we get a better estimate of it near the LRS field point? Extrapolate from MIMF sensing near there?

• Update LRS slit geometry for better consistency with SIAF

[mperrin]

miri_siaf = pysiaf.Siaf('MIRI')
ap_slit = miri_siaf.apertures['MIRIM_SLIT']  # SLIT aperture type, does not have coordinates in det frame defined

slit_width = (ap_slit.XIdlVert4+ap_slit.XIdlVert3)/2 - (ap_slit.XIdlVert1+ap_slit.XIdlVert2)/2
slit_height = (ap_slit.YIdlVert2+ap_slit.YIdlVert3)/2 - (ap_slit.YIdlVert4+ap_slit.YIdlVert1)/2

slit_width, slit_height
> (4.72345, 0.51525)

versus currently in webbpsf:
(<Quantity 4.7 arcsec>, <Quantity 0.51 arcsec>)

[mperrin]

Much, but not all, of the improvement ideas noted in this issue were implemented in #787. The others may remain pending for some future improvement.