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

[Eric Greisen]

Eric Greisen updated #16728
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       Staff (Owner): Eric Greisen (was: -- Unassigned --)

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): Eric Greisen
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template group: Default
             Created: 06 August 2020 11:49 AM
             Updated: 13 August 2020 02:44 PM
           Reply due: 17 August 2020 01:12 PM (3d 22h 28m)
      Resolution due: 02 May 2023 05:00 PM (992d 2h 15m)

I think I am confused by what Is plotted in the plots you sent.  I had assumed that the "bad" one (with horns at +- 45 and 135) was every single time stamp and every single channel individually.  That would be rather noisy in phase if the sources are fairly weak even if SPW averaged data are well detected.  The AIPS task UVHIM will make a histogram image - you can try with real/imag and amp/phase axes.  A rectangle in real/imag is what I would expect if the noise is the same in both real and imag (as it should be).  RFLAG looks for specific signatures in the data (or at least the CASA version used to).  If your calibrators are not point sources then some of the phase variation may also be due to their structure.  Try SPFLG to look at your data in detail also.  Are there systematic oddities or occasional unflagged RFI?
Just some random thoughts...
Eric Greisen


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