[daip] [!16728]: AIPS - Help Explaining Phase Calibrator Plots

[Gregory Walsh]

Help Explaining Phase Calibrator Plots
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           Ticket ID: 16728
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/16728
                Name: Gregory Walsh
       Email address: gwalsh4758 at gmail.com
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): -- Unassigned --
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template group: Default
             Created: 06 August 2020 06:49 PM
             Updated: 13 August 2020 08:12 PM
           Reply due: 17 August 2020 08:12 PM (4d 0h 0m)
      Resolution due: 03 May 2023 12:00 AM (992d 3h 47m)

Hi Eric,

Sorry for taking a while to respond. Had some computer issues that I 
needed to fix over the past few days.

The real vs. imaginary plots are not what I expected to see; they form a 
rectangle which is centered <0 for the real axis (which seems good), and 
at 0 for the imaginary (again, seems good). The shape is kind of 
throwing me for a loop.

For the most part the diagnostics I've looked at, such as amplitude vs. 
uv distance, don't look unreasonable. I examine the gain phase solutions 
for each phase calibrator when I calibrate the data in AIPS and, besides 
very sparsely, the phase solutions are flat and don't seem to be 
clustered around +/- 45, 135. Overall, I don't think this is a serious 
issue (we're still getting results) but it is very strange.

On your point about the individual channels, pretty much every single 
phase calibrator (2 per target) for every observation (about 130) in 
each frequency band (C-band and S/X dichroic receiver) looks like this 
when I examine the phase vs. amplitude plot.  This issue seems too 
pervasive and consistent to just be from individual channel noise 
scattering, though I do agree this would cause an issue.

If it is from scattering in individual channels, automated flagging 
routines should remove these spurious data points, correct? Do you think 
re-calibrating the data after flagging these points would improve the 
issue? It could be that I am being led astray in my diagnostics by the 
fact that these points have already been removed.

Thank you,

Greg




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