National Radio
Astronomy Observatory

4.2.3 The Calibration of VLA data in CASA

CASA supports the calibration of VLA data that is imported from the Archive through the importvla task. See § 2.2.3 for more information.

ALERT: Data taken both before and after the Modcomp turn-off in late June 2007 will be handled automatically by importvla. You do not need to set special parameters to do so, and it will obey the scaling specified by applytsys.

You can also import VLA data in UVFITS format with the importuvfits task (§ 2.2.4.1). However, in this case, you must be careful during calibration in that some prior or previous calibrations (see below) may or may not have been done in AIPS and applied (or not) before export.

For example, the default settings of AIPS FILLM will apply VLA gaincurve and approximate (weather-based) atmospheric optical depth corrections when it generates the extension table CL 1. If the data is exported immediately using FITTP, then this table is included in the UVFITS file. However, CASA is not able to read or use the AIPS SN or CL tables, so that prior calibration information is lost and must be applied during calibration here (ie. using gaincurve=True and setting the opacity parameter).

On the other hand, if you apply calibration in AIPS by using the SPLIT or SPLAT tasks to apply the CL tables before exporting with FITTP, then this calibration will be in the data itself. In this case, you do not want to re-apply these calibrations when processing in CASA.

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

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