Description

apply calibrations solutions(s) to data

Summary

The applycal task reads the specified gain calibration tables, applies them to the (raw) MS DATA column (with the specified selection), and writes the calibrated data into the CORRECTED_DATA column, where imaging or other analysis can find it for further processing. All supplied calibration is applied in one step, according to the Measurement Equation. The existing contents of the CORRECTED_DATA (for the specified selection) will be overwritten.  

The applycal task shares the input dataset ('vis'), data selection and (prior) calibration parameters with the solving tasks; detailed information about setting these parameters can be found the section on "Solving for Calibration". Several parameters unique to applycal are described below.

In the traditional interface (docallib=False), all calibration tables (both temporal, frequency, polarization calibrations) are specified in the gaintable parameter. The calibration values associated with a restricted list of fields can also be selected for each table in gainfield. As of CASA v4.2, docallib=True provides specification of an ensemble of calibration tables and directives via a cal library file.

After running applycal, the corrected data may be selected, partially (and optionally) averaged, and copied to a new MS using mstransform (formerly split). This may be desirable to reduce the size of the dataset for further processing, if circumstances (e.g., field-of-view) permit. Alternatively, the corrected data may be imaged directly from the original MS.

Calibrated data may be examined in plotms and visstat.

 

Weight calibration: calwt

Unlike the solving tasks, calibration of the weights is optional in applycal, and is controlled using the calwt parameter. If calwt=True, the weights will be calibrated by all specified caltables that change the data's scale (phase-like caltables have no effect on the weights). The calwt parameter may also be specified as a list of Booleans, enabling control of which caltables calibrate the weights. In general, it is advisable to calibrate the weights, as this should ensure achieving the full natural sensitivity of the observation. Information about weight calibration conventions can be found here.

Calibration application modes: applymode

The applycal task supports different modes of application via the applymode parameter:

  • 'calflag' will apply all flags from a calibration table to the MS and apply the calibration itself to the remaining visibilities (and weights, as per calwt). This is the default.
  • 'trial' will only report on the calibration table flags but not manipulate the data or weights.
  • 'flagonly' applies the flags but not the calibration itself, leaving the data and weights untouched.
  • 'calonly' will apply the calibration to data and weights, but leave the flags untouched.

For the flag-aware options, if 'strict' is appended (e.g., 'calflagstrict' or 'flagonlystrict'), applycal will flag all selected data for spws that have no solutions available in any one of the caltables, instead of allowing the to pass uncorrected and unflagged. 

Flag control: flagbackup

Since the MS stores only one copy of the flags (in the FLAG column), saving flags prior to applycal is often desirable. Use flagbackup=True for this. The pre-applycal flags will be stored in a separate CASA table named for the MS, with a '.flagversions' suffix. See the flagmanager task to recover old flag versions and otherwise manage the flag information.