This note records the validation scope for the synthetic-emission extensions in mod_thermal_emission.

Compatibility baseline

The default &emissionlist behavior remains unchanged:

radiation_transfer='thin'
ray_method='auto'
dat_resolution_mode='nominal'
emission_model='auto'
output_tau=.false.
output_absorption_fraction=.false.
instrument_postprocess=.false.
radio_frequency=17.d9
radio_beam_fwhm=0.d0
radio_beam_pixel_size=0.d0

Existing convert_type='SI...' and WI... inputs continue to use the historical paths. EUV images use ray_method='auto' by default: Cartesian dat-resolution EUV uses the native Cartesian ray tracer, spherical EUV uses the native spherical ray/mesh-intersection path, and unsupported combinations fall back to legacy. Set ray_method='legacy' to force the old projector.

Current product matrix

The current implementation is intended to keep the historical workflow (convert_type plus &emissionlist) while adding explicit transfer and ray choices for Cartesian post-processing.

Product	Legacy instrument grid	Cartesian dat-resolution	Cartesian cart arbitrary LOS	Thick transfer	Post-process to observational grid	Spherical
EUV AIA/IRIS/EIS image	yes, thin	yes, axis-aligned thin/thick	yes, thin/thick	yes, H/He absorption	yes, AIA-style PSF for Cartesian native EUV images	legacy thin plus native spherical thin/thick EUV instrument-grid and dat-resolution
SXR image	yes, thin	yes, axis-aligned thin	no	no	no native post-process	legacy thin instrument-grid only
White light	spherical legacy	no	no	no	legacy LASCO-like PSF	yes, primary supported path
radio_ff	limited through EUV image path	yes	yes, thin/thick	yes	yes, independent Gaussian radio beam	no native support
pseudo_current	limited through EUV image path	yes	yes, thin only	no	no	no native support

Practical recommendations:

For cold-material EUV absorption in Cartesian data, use radiation_transfer='thick'; for non-axis-aligned views, also use ray_method='cart'.
For dat-resolution data with non-uniform output spacing, use VTU output. VTI is allowed only when the emitted image-plane grid is uniform.
For radio quick-look products, the current radio_ff path is sufficient for multi-view brightness-temperature images. Use radio_beam_fwhm only when an observational beam is needed.
For spherical data, use the legacy instrument-resolution projection for optically thin SXR and white light. For native EUV ray tracing, use ray_method='spherical' with radiation_transfer='thin' or 'thick'; both instrument-resolution and dat-resolution EUV images are supported.

Local demo guards

The radiation-synthesis examples documented here are intended as local demo and developer guards. They are not wired into the top-level autotest/CI suites by default, because the full 3D convert cases are heavier than the regular regression matrix.

3D demo case

The Cartesian demo case is tests/demo4/RadiationSynthesis_3D. It builds a small TDm/prominence AMR cube and keeps two thick EUV reference views:

axis-aligned optically thick AIA 171 image with tau and absorption_fraction, using convert_171_thick.par.
oblique native Cartesian optically thick AIA 171 image with tau and absorption_fraction, using convert_171_cart_dda_thick_oblique.par.

Run the 3D Cartesian demo manually with:

make -C tests/demo4/RadiationSynthesis_3D -f test.make

The generated VTI files are intended for visual inspection in ParaView rather than as bit-for-bit regression baselines.

Performance baseline

The current performance-sensitive paths are:

axis-aligned thick transfer, which streams LOS layers in small batches instead of allocating a full Npix * Nlos column buffer.
cart, which preselects block footprints on the image plane and routes per-pixel ray segments to owner MPI ranks before sorting. It emits lightweight profile counters for ray tests, ray hits, segment counts, MPI exchange volume, and sorting work in the per-conversion logs.

For quick performance comparisons, use the same TDm/prominence demo case and record wall time for the retained reference conversions:

convert_171_thick.par
convert_171_cart_dda_thick_oblique.par

The most useful next profile points are ray-box intersection counts, collected segment counts, MPI_ALLTOALLV volume, and same-pixel segment sorting time.

Spherical-coordinate support

The legacy spherical path is the historical instrument-resolution projector. It initializes a LOS/image-plane basis from LOS_theta, LOS_phi, and image_rotate, sub-samples spherical cells in r/theta/phi, maps each sub-sample to the image plane, and distributes the contribution through the instrument PSF. A native ray/mesh-intersection path is also available for EUV images with ray_method='spherical'.

Supported today:

optically thin EUV instrument-resolution images on spherical grids.
native spherical thin and thick EUV images with ray_method='spherical' and radiation_transfer='thin' or 'thick'; both instrument-resolution and dat-resolution image grids are supported.
spherical thick EUV diagnostic maps tau and absorption_fraction.
optically thin SXR instrument-resolution images on spherical grids.
LASCO-like white-light B and pB images on spherical grids.
EUV spectra on spherical grids through the legacy instrument-resolution spectral path.
occultation/opaque-inner-region handling through R_opt_thick for EUV/SXR visibility checks and the white-light occultor parameters for LASCO products.

Not supported yet:

spherical .dat-resolution SXR images.
cart on spherical data.
instrument_postprocess on spherical data.
radio_ff or pseudo_current as validated spherical products.
spherical for SXR, white light, radio, pseudo-current, polar-axis crossing domains, or phi-wrapping domains.

The native spherical path constructs ray intersections with spherical grid faces, sorts path points by LOS distance, and in thick EUV mode reuses the j/kappa transfer layer for strict front-to-back integration. It still rejects polar-axis crossing, phi-wrapping, and non-EUV products.

The spherical demo case is tests/demo4/RadiationSynthesisSphericalTDm_3D. It builds a lightweight spherical TDm/prominence-style AMR shell and keeps two native spherical thick EUV reference views:

top-down thick AIA 171, using convert_171_sph_native_topdown_thick.par.
45-degree top-corner thick AIA 171, using convert_171_sph_native_corner45_top_thick.par.

Run the spherical demo manually with:

make -C tests/demo4/RadiationSynthesisSphericalTDm_3D -f test.make

The generated VTI files contain AIA171_thick, tau, and absorption_fraction and are intended for ParaView inspection.

Remaining known scope limits

cart currently requires Cartesian slab dat-resolution grids.
Dat-resolution VTI output is restricted to uniform image-plane spacing; use VTU for non-uniform image grids.
spherical currently supports only spherical EUV images. In dat-resolution mode it outputs AIA intensity, plus optional tau and absorption_fraction in thick mode; Doppler and instrument post-processing are not yet defined for this path.
The old names cart_dda and sph_intersection are accepted as aliases for cart and spherical.
pseudo_current is optically thin only.
radio_ff is a first thermal free-free implementation with a compact Gaunt-factor approximation, brightness-temperature output, and optional Gaussian beam post-processing.