[evlatests] Progress on WIDAR Imaging Woes

[Barry Clark]

So, just looking at this channel on baseline 18-28 as a function of time
should show distinct amplitude states.  We should be able to see this
easily at various stages of processing.  It would even be pretty easy
to toss together a test program using Allen Faris's bdf reader to see
it in the bdf.

Rick Perley wrote:
[snip]
> 
>     2b) Plotting the real vs. the imaginary parts yields more remarkable 
> results.  The differentials fill two rings in the complex plane, 
> corresponding to the two different amplitudes noted above.  Plotting 
> individual baselines in the complex plane shows that each the 
> indidividual data points from each scan cluster at a particular location 
> in the two rings, but each scan's cluster is in a different place.  That 
> is, the error either changes slowly in time, or from scan to scan.  
> (There are five scans at each offset position, separated by about 12 
> minutes).    For some of the shorter baselines, the 'clusters' clearly 
> move around the ring in a orderly fashion.    It is interesting that for 
> baseline 25 x 28, the clusters are oriented vertically --- that is, the 
> real part of the error is zero, the imaginary part is found in one of 
> four different places -- equal to the true amplitude, or its negated 
> value, or double the true amplitude, or its negated value. 
> 
>     I believe that these characteristics are sufficient to explain all 
> the imaging characteristics that we have seen, at all bands.  What has 
> not yet been discovered is how this problem is generated.  George has 
> confirmed that CASA sees the same effects.  He has already shown that by 
> removing all data from these two antennas, the images are vastly 
> improved, and background sources are properly showing up. 
> 
>    
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