[evlatests] [Ecsv] Summary of Polarization Meeting

[Sanjay Bhatnagar]

On Fri, Jul 16, 2010 at 3:12 PM, George Moellenbrock <gmoellen at nrao.edu> wrote:
>
>> An importance point is that, for the VLA, it is very
>> unlikely that the *absolute* Ds can be derived as a matter of course
>> from ordinary observations -- by construction, all antennas view the
>> sources at the same parallactic angle, making impossible, or at least
>> highly unlikely, a robust method for extracting the absolute Ds.  By
>> necessity, all 'Ds' determined from standard interferometry are
>> referenced to a standard -- either a global mean (CASA, MIRIAD), or a
>> particular antenna (AIPS).
>
> Well, I'd hope to say "tricky" rather than "unlikely".  _Polarized_
> calibrators are required (unpolarized calibrators provide only the
> additional DDI term in the parallel hands, which cannot be
> completely decoupled from the gain calibration if the mean departure from
> polarization purity is non-zero), and quite probably some iteration with

Devising a joint solver for G and D-Jones is not hard (the LeakyCal
algorithm is basically that) and with certain very reasonable
assumptions, even this decoupling is possible.

That said, for the purpose of applying the corrections, this
de-coupling is not really required.

Sanjay

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