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Simulating MID direction dependent gain effects

SPO-1057

SIM team

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ska-mid-simulations

  • SKA gitlab repository
  • Small number of scripts based on RASCIL
  • Generates MeasurementSets with error on, error off, and difference visibilities
  • Uses Dask for distributed processing, SLURM available for job management
  • Results available on Google Cloud Platform

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Steps in simulation

  • Make a fake sky of point sources or find sources in CLEAN image
  • Loop over all sources
    • Calculate relative az, el of each point source as a function of time
    • Calculate effective voltage pattern in Dish coordinate system Jones matrix image as gaintable
    • Apply gaintable to visibility
  • Sum visibility over all sources and all times
  • Distribute processing using Dask

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SKA and MeerKAT polarised beams: real

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SKA and MeerKAT polarised beams: imaginary

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Effects

  • Hetergeneous dishes
  • Elevation-dependent dishes
  • Troposphere and ionosphere
  • Polarisation leakage
  • Wind-induced pointing
  • Random pointing

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Example driver script

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Ionosphere

  • 350 MHz Band B1 Mid observations
  • Difference visibility

Sorted by baseline

Sorted by baseline length (m)

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Heterogeneous array

  • SKA1 and MeerKAT dishes differ in diameter, illumination
  • On - off visibility for polarisations XX, XY, YX, YY

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Difference Stokes I

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Difference Stokes Q

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Difference Stokes U

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Difference Stokes V

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Polarisation leakage

  • X, Y electric fields leak into each other
  • e.g. Stokes I leaks into Q, U, V images
  • AND Voltage pattern rotates on sky with parallactic angle
  • Can we correct if we know the voltage beam well enough?

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I = (XX+YY)/2

Q = (XX-YY)/2

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Adding new effect

  • Create function to generate on, off gaintables
  • Call function from ska-mid-simulations:src/mid_simulation.py
  • Add implementation to RASCIL
  • Rsexecute = wrapped Dask