hifa_polcal

hifa_polcal(vis=None, minpacov=None, solint_chavg=None, vs_stats=None, vs_thresh=None) → PolcalResults[source]

Perform per-session polarization calibration for ALMA.

Derives the instrumental polarization calibrations using the polarization calibrators. This task is called once per session (which for ALMA polarization observations is typically 2-3 execution blocks).

The WebLog displays the following tables:

  • Session information: MeasurementSets, polarization calibrator, and reference antenna per session.

  • Residual polarization of the calibrator after calibration (per spw and averaged over all spws).

  • Derived polarization of the calibrator (per spw and averaged over all spws).

And the following plots per session for the polarization calibrator:

  • Amplitude vs. parallactic angle per spw

  • Gain amplitude polarization ratio vs. scan

  • Cross-hand phase vs. channel

  • D-term solution gain vs. channel per spw for all antennas

  • Gain ratio RMS vs. scan

  • X,Y amplitude vs. antenna per spw

  • X/Y amplitude gain ratio vs. antenna per spw

  • Real vs. imaginary component of the calibrated polarization calibrator (XX, YY, XY, YX)

WebLog QA for hifa_polcal

Example of the WebLog QA for the hifa_polcal stage.

Parameters:

  • vis --

    The list of input MeasurementSets. Defaults to the list of MeasurementSets specified in the pipeline context.

    Example: ['M32A.ms', 'M32B.ms']

  • minpacov --

    Minimum Parallactic Angle Coverage (degrees) required for Q, U estimation in task polfromgain. This enables avoiding pathological cases of antennas with insufficient parallactic angle coverage which can yield spurious source polarization solutions or cause polfromgain to fail to find any solutions.

    Default: 30.0

  • solint_chavg --

    Channel averaging to include in solint for gaincal steps producing cross-hand delay, cross-hand phase, and leakage (D-terms) solutions.

    Default: '5MHz'

  • vs_stats --

    List of visstat statistics to use for diagnostic comparison between the concatenated session MS and individual MSes in that session after applying polarization calibration tables.

    Default: ['min','max','mean']

  • vs_thresh --

    Threshold to use in diagnostic comparison of visstat statistics; relative differences larger than this threshold are reported in the CASA log.

    Default: 1e-3

Notes

Four QA scores are computed:

  • Residual polarization: QA = 0.5 (yellow) if residual polarization > 0.1%; QA = 1.0 otherwise.

  • Gain ratio RMS: QA = 0.6 (yellow) if gain ratio RMS after calibration > 2%; QA = 1.0 otherwise.

  • D-terms: QA = 0.75 (blue) if D-terms 0.10-0.15; QA = 0.55 (yellow) if > 0.15; QA = 1.0 otherwise.

  • Gain ratio: QA = 0.65 (yellow) if any antenna/spw gain ratio outside 0.9-1.10; QA = 1.0 otherwise.

Only used in polarization recipes.

Returns:

The results object for the pipeline task is returned.

Examples

  1. Compute the polarization calibrations:

>>> hifa_polcal()