<div dir="ltr"><div><div><div><div><div><div>I've been contemplating pretty much what Barry suggests, with some<br></div>additional attention paid to what the R-L phase might do. The <br>practical point of a reference 'antenna' is two-fold: enforce<br>
interpolatable continuity among solutions as a function of time<br></div><div>(i.e., the presumption made when choosing the calibrator cadence),<br></div>_and_ (for polarimetry) enforce some sense of R-L phase stability<br>
</div><div>(a presumption we are fond of, and which is probably reasonable, <br>but which we have not really quantified from a commissioning point <br>of view, to my knowledge). <br><br></div>Relying on any single antenna (for all subbands for whole<br>
observations) will often be problematic (flagging), and a single<br>antenna probably isn't the formally best R-L reference, in general. <br>The upshot is probably that a traditional referencing with a specific<br>antenna is applied at a specific time (to establish a definite frame), <br>
and then minimum median deviation (over time) and median R-L stability<br></div><div>(over fields) over the _ensemble_ of available antennas is enforced. This is<br>a stronger and less vulnerable realization of the presumptions<br>
we want to make. Use of medians in this enforcement will render <br>any minority of misbehaving antennas (including phase jumps, and<br>also other more-subtle pathologies like differential phase drifts) <br>(a) irrelevant to the referencing operation itself, and (b) more <br>
plainly obvious for flagging or exclusion purposes.<br><br></div><div>For the R-L part of all of this, external factors like the ionosphere<br></div><div>have to be accounted for separately, of course.<br><br>-George<br>
<br></div><div><br></div></div></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Wed, Apr 24, 2013 at 8:57 AM, Barry Clark <span dir="ltr"><<a href="mailto:bclark@nrao.edu" target="_blank">bclark@nrao.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Perhaps the better long term solution is to get rid of the concept of<br>
reference antenna for pipeline purposes. Phase solutions are<br>
intrinsically floating (that is, the matrix is singular). Assuming<br>
one antenna has phase zero is one way of supplying the extra bit of<br>
information to make the solution possible; more particularly, assuming<br>
one antenna doesn't have phase jumps is one way to tie two phase<br>
solutions together. For lots of antennas, a better way is to say<br>
that the mean change for all antennas is zero. (Probably one would<br>
want to use one of the robust means.)<br>
<div class="HOEnZb"><div class="h5"><br>
On 04/24/2013 07:31 AM, Claire Chandler wrote:<br>
> We are working on this from the pipeline side, but at the same time, such<br>
> things need to be fixed from the technical sided as well. The pipeline is<br>
> part of end-to-end operations now. It really does try to do something<br>
> sensible in picking a refant -- it is based on location in the array and<br>
> the amount of unflagged data (to avoid picking an antenna that is shadowed<br>
> or missing a receiver). But it cannot test for phase jumps. I don't<br>
> think using the same on as Telcal is always going to work either. We are<br>
> working on providing a list of antennas that it should NOT use.<br>
><br>
> Claire<br>
><br>
> On Wed, 24 Apr 2013, Michael Rupen wrote:<br>
><br>
>> In general it would be nice if the pipeline were smarter about choosing<br>
>> reference antennas. ea14 should of course be fixed, but one bad antenna<br>
>> should not produce such a "ripple effect" downstream.<br>
>><br>
>> The intelligent choice of a ref.ant. is not entirely trivial.<br>
>> An interim solution might be to use the same antenna we use as a reference<br>
>> for TelCal, which we tend to keep a careful eye on operationally.<br>
>> This has the benefit of matching the reference used for phased array<br>
>> work. That reference antenna at the moment is ea12, but might more<br>
>> usefully be described as the antenna on pad E8 -- one of the three<br>
>> antennas which is never moved when we change configurations, and central<br>
>> enough when it matters (i.e., for the more extended configurations).<br>
>><br>
>> There is no obvious place in the SDM proper at the moment to store the<br>
>> suggested reference antenna. We might consider adding an element to the<br>
>> ExecBlock Table to handle this:<br>
>><br>
>> Optional:<br>
>> numRefAntenna int<br>
>> refAntenna[Nrefant], Tag[Nrefant]<br>
>> description: "default reference antennas for calibration, in order<br>
>> of preference"<br>
>><br>
>> We actually do send such suggestions to TelCal at the moment, so recording<br>
>> that information (esp. useful for phased-array data) would seem reasonable.<br>
>><br>
>> Michael<br>
>><br>
>>> Hi All,<br>
>>><br>
>>> We are seeing phase jumps on EA14 and right now the pipeline is choosing<br>
>>> EA14 as a reference antenna so, when there is a phase jump, the pipeline<br>
>>> output is not usable.<br>
>>><br>
>>> Is there anyway someone can go out to EA14 on Maintenance day tomorrow to<br>
>>> see if this can be fixed?<br>
>>><br>
>>> Thanks,<br>
>>> Deb<br>
>>><br>
>>><br>
>>><br>
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