National Radio
Astronomy Observatory

2.4 simulator - Module

Module for simulation of telescope data

Description

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 or through specified errors reading in (anti-) calibration tables.

In the observing phase, simulator tries to act like a (simple) telescope. You first open the name of the MeasurementSet that you wish to construct. Next you use the various set* methods to setup the observing (sources, spectral windows, etc). Each such setup should be given a unique name that will be used in the next step. Then you call the observe method for each observing scan you wish to make. Here you specify the source name, spectral window name, and observing times. After this, you have a MeasurementSet that is complete but empty. In the next phase, you fill the MeasurementSet with data from a model and then corrupt the measurements (if desired). To fill it in with a model, use the predict method. Finally, to apply errors, first set up the various effects using the relevant set* methods and then call corrupt.

Some important points:

• One call to observe generates one scan (all rows have the same SCAN_NUMBER).
• The start and stop times specified to observe need not be contiguous and so one can siulate antenna drive times.
• Currently there is no facility for patterns of observing, such as mosaicing, since it is easy to do this via sequences of calls of observe.

The following columns of the MeasurementSet are particularly important:

• DATA The original observed visibilities are in a column called DATA. These are normally not altered by any processing in CASA. simulator does write this column when it creates observations.
• CORRECTED_DATA During a calibration process, the visibilities may be corrected for calibration effects. These corrected visibilities are stored in CORRECTED_DATA which is created upon demand.
• MODEL_DATA During various phases of processing, the visibilities as predicted from some model are required. These model visibilities are stored in the column MODEL_DATA. The ’ft’ task can be used to calculate the model visibilitiy for a model image.

The available tool in this module is:

• Simulator - tool for simulation

More information about CASA may be found at the CASA web page

Copyright © 2016 Associated Universities Inc., Washington, D.C.

This code is available under the terms of the GNU General Public Lincense