Compute coherency matrix
While Anime focuses on generating instrument models, this example is provided as a "passive" example for the user to run on their local machines. This function cannot be used if WSClean is not installed. Usage of external sofware will soon be replaced by native computation of source coherency matrices written in Julia.
The Radio Interferometer Measurement Equation (RIME)[HBS][OMS] lies at the heart of modelling interferometric observations. A generic discrete RIME can be written as
\[\mathbf{V}_{pq} = G_p \left( \sum_{s} E_{sp}\, \mathbf{X}_{spq}\, E_{sq}^H \right) G_q^H,\]
where the summation is carried out over all the sources $s$, and $\boldsymbol{E}_{sp}$ and $\boldsymbol{G}_p$ denote generic direction-dependent effects (DDEs) and direction-independent effects (DIEs) respectively. Each term is a $2\times2$ Jones matrix that describes any linear transformation acting on the incoming wave, and $H$ is the Hermitian conjugate. $X_{spq}$ is the source coherency matrix given by
\[X_{spq} = \mathrm{B} e^{-2\pi i (u_{pq}l + v_{pq}m + w_{pq}(n-1))}; \mathbf{u}_{pq} = \mathbf{u}_p - \mathbf{u}_q\]
where $\mathrm{B}$ is the brightness matrix, $l$, $m$, $n$ are direction cosines, and $\mathbf{u}_{pq}$ are the baseline $uvw$ coordinates.
While computing instrument models is the main aim of Anime we also provide a way to compute source coherency matrices by calling the external program WSClean:
using Anime
msname = "eht.ms" # path to existing Measurement Set
skymodel = "grmhdpol" # path to existing sky model; samples are available in the `inputs/` directory in the source code
polarized = true
channelgroups = 1
oversamplingfactor = 8191
run_wsclean(msname, skymodel, polarized, channelgroups, oversamplingfactor)References
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