Pointing-offset Simulation

These scripts simulate MID pointing offset observations for 5-point (or more) scans and prepare the simulation data for Pointing-Offset Pipeline.

  • The users could define the radio source and observational time.

  • The observation is for MID-AA0.5 telescope layout over a range of hour angles.

  • Dask is used to distribute the processing over several workers.

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

The core simulation functions reside in RASCIL. The RASCIL driver script in this repository is /src/mid_simulation.py. This can be run directly using the command line arguments listed below, or bash scripts, which have been provided in the pointing_offset directory. The bash scripts allow for looping over observational duration and source coordinate (RA and DEC). Before using the scripts, the users could modify observatory location, point source coordinate, integration time, time chunk, and so on.

Note that the simulation has four steps:

  1. Calculate 5-point pointing directions (RA/DEC) according to the given offset values, source RA, source DEC, and observation time.

  2. Generate Gaussian Voltage Pattern FITS files.

  3. Simulate pointing offset data (MeasurementSet format) using mid_simulation.py and generate relevant HDF files.

  4. Add SOURCE OFFSET and relevant tables in the MS files.

The simulation can be run in any PC servers. According to the number of channels, the amount of memory is quite important for the simulation. According to the current simulation results, the size of voltage pattern files (real or imagined part) of 8, 256, 1024, and 16384 channels is about 268 MB, 859 MB, 3.43 GB, and 549 GB, respectively.

MeasurementSets (MS), FITS, and HDF5 files save the results. Currently, MS files are generated to store actual and nominal data and their differences. HDF5 files include primary beam components and actual, nominal, and source gaintable files. In the simulation, nominal files mean the expected values and actual data means the expected + pointing offset values. The Voltage Pattern (VP) files are stored in FITS format.

The FITS file can be viewed using the casaviewer or carta <https://cartavis.org/> `_. The MS file can be viewed using the `casaviewer as well.

If the user wants to run on a local machine, make sure to setup the below environment variables:

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

The default for these variables is set as common directories on the HPC.

Script Descriptions


  • Calculate RA and DEC according to the 5-point observation requirements. AstroPy is used in the position calculation.

  • Output data files are used in the simulation.


  • A point source is simulated, and the relevant voltage pattern is applied before the Fourier transform.

  • Simulates observations with SKA1-MID AA0.5.

  • stokesIQUV, Band B2


  • A shell script to run the simulation.

For more details, see: https://confluence.skatelescope.org/display/SE/Pointing+Offset+Simulation+Using+SKA-SIM-MID