Continuum imaging

These scripts simulate MID continuum imaging observations of multiple point sources.

The sky model is constructed from Oxford S3-SEX catalog. These are unpolarised point sources.

The observation is by MID or MEERKAT+ over a range of hour angles.

The visibility is calculated by Direct Fourier transform after application of the gaintable for each source.

Dask is used to distribute the processing over a number of workers.

Processing can be divided into chunks of time (default 1800s).

The core simulation functions reside in RASCIL. The RASCIL driver script for simulation in this repository is direction_dependent/src/mid_simulation.py. This driver scripts can be run directly using the command line arguments listed below. Canonical bash scripts have been provided in continuum_imaging/scripts. The scripts will need to be altered for location of the various files needed. We recommend use of the bash scripts at first.

These simulations typically requiring a cluster to run. In Cambridge They work well on the P3 cluster using 16 nodes of 128GB each.

There are types of output: MeasurementSets and Images. Each are calculated for actual, nominal, and difference. The time consumed in the calculation of the MeasurementSets is small compared to the time in writing the MeasurementSet and the time to make the images. Images may be calculated using the dist_imager.

The fits images can be viewed using the casaviewer or carta. The MeasurementSets can be viewed using casaviewer.

If you are running on your own machine, make sure you have the below environment variables set up:

SSMROOT : location where the ska-sim-mid repository is SSMRESOURCES : location of the resources e.g. beam models SSMRESULTS: location of results folder

Effects simulated

Nominal

A set of point sources is simulated and the relevant nominal voltage pattern for each end of interferometer is applied before Fourier transform. The nominal pattern is constructed from a tapered symmetric illumination pattern, with the diameter of the SKA dishes.
stokesIQUV, band B2

Heterogenous

A set of point sources is simulated and the relevant voltage pattern for each end of interferometer is applied before Fourier transform.
Simulates observations with all SKA and MEERKAT dishes (on state) and all SKA dishes (off state).
stokesIQUV, band B2

Heterogenous_meerkat+

A set of point sources is simulated and the relevant voltage pattern for each end of interferometer is applied before Fourier transform.
Simulates observations with MEERKAT+ configuration, all SKA and MEERKAT dishes (on state) and all SKA dishes (off state).
stokesIQUV, band B2

Ionosphere

A set of point sources is simulated and the phases calculated using a thin screen model for the ionosphere. The screen has units of meters of Total Electron Content. The phase is evaluated at places in the screen where the line of sight from source to a dish pierces the screen.
Simulates observations with ionospheric screens on and off.
This requires the screens to be calculated first or downloaded: see ../screens/README.md
stokesI, band B1LOW

Polarisation

Simulates observations with SKA and EMSS calculated primary beam models with cross pol (on) and no cross pol set to zero (off)
Polarisation stokesIQUV, linear, band B2

Surface sag

Simulates observations with sagging dish (on) and nominal dish (off).
Models of the voltage pattern are available at +15, +45, +90 deg elevation.
We interpolate between those to 5 degrees.
Stokes I, band B2

For more details see: https://confluence.skatelescope.org/display/SE/Dish+deformation+simulations

Troposphere

Simulates observations with tropospheric screens on and off.
This requires the screens to be calculated first or downloaded: see ../screens/README.md
stokesI, bands B2 and B5
A set of point sources is simulated and the phases calculated using a thin screen model for the atmosphere. The phase is evaluated at places in the screen where the line of sight from source to dish pierces the screen. The screen has units of meters of delay.

Wind pointing

Simulates observations with wind buffeting of dishes (on) and without (off)
Stokes I, bands B2 and B5

For more details see: https://confluence.skatelescope.org/display/SE/MID+pointing+error+simulations

Simulate SKA-MID direction dependent errors

usage: mid_simulation.py [-h] [--rmax RMAX] [--image_sampling IMAGE_SAMPLING]
                         [--configuration CONFIGURATION]
                         [--antennas [ANTENNAS ...]] [--source SOURCE]
                         [--ra RA] [--declination DECLINATION] [--band BAND]
                         [--nchan NCHAN] [--channel_width CHANNEL_WIDTH]
                         [--integration_time INTEGRATION_TIME]
                         [--time_range TIME_RANGE TIME_RANGE]
                         [--time_step TIME_STEP] [--make_images MAKE_IMAGES]
                         [--only_actual ONLY_ACTUAL] [--apply_pb APPLY_PB]
                         [--pbtype PBTYPE] [--seed SEED]
                         [--flux_limit FLUX_LIMIT] [--npixel NPIXEL]
                         [--cellsize CELLSIZE] [--weighting WEIGHTING]
                         [--robustness ROBUSTNESS] [--results RESULTS]
                         [--elevation_sampling ELEVATION_SAMPLING] [--r0 R0]
                         [--height HEIGHT] [--screen SCREEN]
                         [--isoplanatic ISOPLANATIC] [--time_chunk TIME_CHUNK]
                         [--channel_start CHANNEL_START] [--mode MODE]
                         [--duration DURATION]
                         [--wind_conditions WIND_CONDITIONS]
                         [--global_pe GLOBAL_PE GLOBAL_PE]
                         [--static_pe STATIC_PE STATIC_PE]
                         [--dynamic_pe DYNAMIC_PE]
                         [--pointing_directory POINTING_DIRECTORY]
                         [--vp_directory VP_DIRECTORY]
                         [--vp_support VP_SUPPORT] [--use_dask USE_DASK]
                         [--write_gt WRITE_GT] [--write_pt WRITE_PT]
                         [--imaging_dft_kernel IMAGING_DFT_KERNEL]
                         [--add_noise ADD_NOISE] [--ra_s RA_S] [--dec_s DEC_S]
                         [--vp_real_file VP_REAL_FILE]
                         [--vp_imag_file VP_IMAG_FILE] [--obs_time OBS_TIME]

Named Arguments

--rmax

Maximum distance of dish from centre (m)

Default: 200000.0

--image_sampling

Number of points per synthesized beam

Default: 3.0

--configuration

MID Configuration: MID | MEERKAT+

Default: “MID”

--antennas

Antenna names to include (default is all)

--source

Type of source: s3sky or point or double

Default: “s3sky”

--ra

Right ascension of phase centre (degrees)

Default: 0.0

--declination

Declination of phase centre (degrees)

Default: -40.0

--band

Band B1LOW | B1 | B2 | B5 | Ku

Default: “B2”

--nchan

Number of frequency channels

Default: 1

--channel_width

Channel bandwidth (Hz) (default is to calculate from band frequency)

--integration_time

Integration time (s)

Default: 180

--time_range

Time range in hour angle

Default: [-4.0, 4.0]

--time_step

Time step (unit: second of time)

--make_images

Make the images?

Default: “True”

--only_actual

Only make the actual data?

Default: “False”

--apply_pb

Apply the primary beam in modes troposphere and ionosphere?

Default: “True”

--pbtype

Primary beam model: MID_B1 MID_B1LOW MID_B2 MID_Ku MEERKAT_B1 MEERKAT_B2 MEERKAT_Ku

Default: “MID_B2”

--seed

Random number seed

Default: 18051955

--flux_limit

Lower flux limit (Jy)

Default: 0.01

--npixel

Number of pixels in the resulting image

Default: 512

--cellsize

Cellsize in radians (will calculate if set to None)

--weighting

Type of weighting (natural, uniform or robust)

Default: “uniform”

--robustness

Robustness for robust weighting

Default: 0.0

--results

Directory for results

Default: “./”

--elevation_sampling

Sampling in elevation for surface (deg)

Default: 1.0

--r0

R0 (meters)

Default: 5000.0

--height

Height of layer (meters)

Default: 300000.0

--screen

Location of atmospheric phase screen data

Default: “/home/docs/checkouts/readthedocs.org/user_builds/ska-telescope-ska-sim-mid/envs/latest/lib/python3.10/site-packages/rascil/processing_components/../../data/models/test_mpc_screen.fits”

--isoplanatic

Are the phase screens to be treated as isoplanatic?

Default: “False”

--time_chunk

Time for a chunk (s)

Default: 3600.0

--channel_start

First channel of interest if interested in some frequency range. Use with –nchan

--mode

Default: “none”

--duration

Type of duration: long or medium or short. Set to custom when using options –integration_time and –time_range (or–time_step)

Default: “long”

--wind_conditions

SKA definition of wind conditions: precision, standard or degraded

Default: “precision”

--global_pe

Global pointing error (absolute values)

Default: [0.0, 0.0]

--static_pe

Multipliers for static errors

Default: [0.0, 0.0]

--dynamic_pe

Multiplier for dynamic errors

Default: 1.0

--pointing_directory

Location of wind PSD pointing files

Default: “/home/docs/checkouts/readthedocs.org/user_builds/ska-telescope-ska-sim-mid/envs/latest/lib/python3.10/site-packages/rascil/processing_components/../../data/models”

--vp_directory

Location of voltage pattern files

--vp_support

Number of pixels in voltage pattern images

--use_dask

Use dask processing?

Default: “True”

--write_gt

Write gaintable files as HDF

Default: “False”

--write_pt

Write pointing table files as HDF

Default: “False”

--imaging_dft_kernel

DFT kernel: cpu_looped | cpu_numba | gpu_raw

--add_noise

Add noises to visibilities

Default: “False”

--ra_s

Right ascension of phase centre (degrees)

Default: -999.99

--dec_s

Declination of phase centre (degrees)

Default: 999.99

--vp_real_file

Voltage pattern real part file name

--vp_imag_file

Voltage pattern imagine part file name

--obs_time

Observation start time