tool simulator description

--CASA Developer--

simulator provides a unified interface for simulation of telescope processing. It can create a MeasurementSet from scratch or read in an existing MeasurementSet, it can predict synthesis data onto the (u,v) coordinates or single dish data onto (ra,dec) points, and it can corrupt this data through Gaussian errors, an atmospheric model, or through specific errors residing in (anti-) calibration tables.

#Import simulator:
import simulator as sm

  1. In sm.observe, simulator creates a MeasurementSet and calculates uvw values. You first make a simulator tool, with the name of the MeasurementSet that you wish to construct. Next you use the various parameters to set up the observing details (sourcename, spwname, starttime, stoptime, etc.). Then you call the sm.observe method for each observing scan you wish to make, or sm.observemany to create several scans. You specify the sourcename, spwname, starttime, and stoptime. After this, you have a MeasurementSet that is complete but visibilities=0.
  2. In sm.predict, you fill a MeasurementSet (either one newly created or a pre-existing one, perhaps from a real telescope) with data from a model or componentlist, and then corrupt the measurements (if desired).

Info: sm.predict assumes model image units are Jy/pixel, and in fact will overwrite the brightness units of the image itself!

The ft method of the imager tool can also be used to calculate the model visibility for a model image or componentlist.

To apply errors, first set up the various effects using the relevant simulator methods, and then call sm.corrupt.

Some important details:

  • One call to sm.observe generates one scan (all rows have the same SCAN_NUMBER).
  • The starttime and stoptime parameters specified to sm.observe need not be contiguous and so one can simulate antenna drive times or other gaps.
  • Currently there is no facility to calculate patterns of observing, such as mosaicing, since it is easy to do this via sequences of calls of sm.observe, or simutil.calcpointings, or the simobserve task
  • The heavy duty columns (DATA, FLAG, IMAGING_WEIGHT, etc. are tiled. New tiles are generated for each scan. Thus the TSM files will not get very large.
  • sm.predict(incremental=False) calculates new visibilities and replaces the DATA column,
  • sm.predict(incremental=True) calculates new visibilities, adds them to the DATA column
  • sm.predict for any value of incremental then sets CORRECTED_DATA equal to DATA, and MODEL_DATA to 1

Numerous methods to facilitate dealing with antenna configuration files, geodetic conversions, mosaic pointing files, etc, can also be found in the simutil class.