[daip] [!9168]: AIPS - clcal introducing amplitude / gain errors

[Amy Mioduszewski]

Amy Mioduszewski updated #9168
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                 Due: - Cleared - (was: 20 October 2016 06:59 PM)
      Resolution Due: 26 October 2016 05:18 PM (was: 26 October 2016 11:18 AM)

clcal introducing amplitude / gain errors
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           Ticket ID: 9168
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/9168
           Full Name: Alexandra Truebenbach
               Email: alexandra.truebenbach at colorado.edu
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): Amy Mioduszewski
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template Group: Default
             Created: 18 October 2016 11:18 AM
             Updated: 18 October 2016 01:35 PM
      Resolution Due: 26 October 2016 05:18 PM (8d 3h 42m)



Hi Alexandra,

There seem to be a couple of effects here.  If the higher and lower amplitude are different sources, then that is OK if the higher amplitude one is expected to be a much brighter source.  The other issue is it seems like there are some bad interpolation between sources, generally amplitude calibration should only be applied to the source it was taken for and there should be no interpolation between sources.  VLBAMP (and VLBACALA) both use INTERPOL='SELF' in CLCAL so the interpolation between sources should not happen, however sometimes Tsys isn't assigned to the correct source. 

Which brings me to the last point, these changes of gain are most likely from the Tsys (TY) table, so you should plot the Tsys table with SNPLT (INEXT='TY'; OPTYPE='TSYS') and see what it looks like, it should be mostly smoothly changing, unless there is a change in source.  If you want to see if you have misassigned Tsys, plot each source separately and see if there are big jumps on an individual source.  You can edit Tsys with either SNEDT, which is an interactive editer, or TYSMO which allows you to clip or smooth the TY table.   It is possible that the problem is in the GC (gain) table, but this extremely unlikely. 


Amy Mioduszewski
NRAO

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