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2.4.1 simulator - Tool

Tool for simulation
Requires:

Synopsis

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 specific errors residing in (anti-) calibration tables. In the observing phase, simulator tries to act like a (simple) telescope. You first make a simulator tool, with the name of the MeasurementSet that you wish to construct. Next you use the various set* methods to set up 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 windoow 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 (mostly for the cognoscenti):

• 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 simulate 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 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.

simulator changes some columns to the MeasurementSet to store results of processing. The following columns in the MS are particularly important:

DATA

The original observed visibilities are in a column called DATA. These are normally not altered by any processing in CASA. However, this simulation program does overwrite these values.

CORRECTED_DATA

During a calibration process, as carried out by e.g. calibrater, the visibilities may be corrected for calibration effects. This corrected visibilities are stored in a column CORRECTED_DATA which is created on demand.

MODEL_DATA

During various phases of processing, the visibilities as predicted from some model are required. These model visibilities are stored in a column MODEL_DATA. The ft function of the imager tool should be used to calculate the model visibility for a model image or componentmodels.

Standard tools such as the table module and the ms can be used to access and possibly change these (and all other) columns.

simulator is a tool that performs simulation of synthesis data, including (optionally) creation of a MeasurementSet, prediction of model data, and corruption by various physical effects.

Methods

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 specific errors residing in (anti-) calibration tables. In the observing phase, simulator tries to act like a (simple) telescope. You first make a simulator tool, with the name of the MeasurementSet that you wish to construct. Next you use the various set* methods to set up 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 windoow 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 (mostly for the cognoscenti):

• 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 simulate 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 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.

simulator changes some columns to the MeasurementSet to store results of processing. The following columns in the MS are particularly important:

DATA

The original observed visibilities are in a column called DATA. These are normally not altered by any processing in CASA. However, this simulation program does overwrite these values.

CORRECTED_DATA

During a calibration process, as carried out by e.g. calibrater, the visibilities may be corrected for calibration effects. This corrected visibilities are stored in a column CORRECTED_DATA which is created on demand.

MODEL_DATA

During various phases of processing, the visibilities as predicted from some model are required. These model visibilities are stored in a column MODEL_DATA. The ft function of the imager tool should be used to calculate the model visibility for a model image or componentmodels.

Standard tools such as the table module and the ms can be used to access and possibly change these (and all other) columns.

simulator is a tool that performs simulation of synthesis data, including (optionally) creation of a MeasurementSet, prediction of model data, and corruption by various physical effects.

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Copyright © 2007 Associated Universities Inc., Washington, D.C.

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