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Basic Information on gpcomb
Purpose: Combine multiple polarization calibration solutions.
GPCOMB combines the leakage tables and xyphase solutions from
multiple calibrators. The routine is intended to be used when
attempting high-precision circular polarization observations at
the ATCA. Because leakages and xyphases are treated as invariant
during circular polarization calibration, a more accurate
calibration may be obtained by averaging several solutions from
several "leakage calibrators".
GPCOMB will probably be less useful for linear polarization
observations, because linear polarization observations are
usually limited by the xygain amplitudes, not the leakages
If the calibration solutions you are comparing had the circular
polarization zero-point determined from different observations
of 1934-638 (eg. on different days), then there may be an
xy-phase offset hidden in the bandpass, and so averaging the
leakages and xyphases would probably be a bad idea. Maybe
try using the same bandpass for both...
And finally, if you have consistent systematic errors in your
solutions (eg. you haven't used xyref,polref in gpcal), then no
amount of averaging is going to help.
For an overview of high-precision circular polarization
calibration with the ATCA, see
Rayner, "Circular Polarization User's Guide", ATNF Technical
Document Series, 2000, 39.3/102,
For thorough treatment of the issues, see
Sault, Hamaker and Bregman, "Understanding radio polarimetry
II. Instrumental calibration of an interferometer array", A&AS,
1996, v117, pp149-159.
The visibility data-set to which the average leakages and
xyphases will be written. If omitted, the averaged
leakage values are still reported to screen.
Existing calibration tables are not applied to vis ie. the
resultant calibration and leakage tables in vis are REPLACED by
those from the cals. This is what you would usually want to
do. If not, apply the appropriate calibration first with uvaver.
The corrected dataset does retain the original gain
amplitude and the antenna-based component of the gain phase.
The data-sets containing the nominally correct polarization
calibration. No default. May include vis.
Normal uv selection. Only antenna-based selection is supported.
If an existing leakage/xyphase solution exists for a de-selected
antenna in vis, the value will be preserved. Otherwise,
it will be set to zero.
Task enrichment parameters. Several can be given,
separated by commas. Minimum match is used.
"noxy" Do not solve for, or apply, the average XY phase.
"nopol" Do not solve for, or apply, average leakages.
Generated by email@example.com on 21 Jun 2016