[daip] [!4536]: AIPS - SNSMO in VLMB mode sometimes breaks the relationship between phase(per IF) and delay

[Michael Bietenholz]

Michael Bietenholz updated #4536
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              Status: Open (was: Closed)

SNSMO in VLMB mode sometimes breaks the relationship between phase(per IF) and delay
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           Ticket ID: 4536
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/4536
           Full Name: Michael Bietenholz
               Email: mbieten at yorku.ca
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): Eric Greisen
                Type: Issue
              Status: Open
            Priority: Default
      Template Group: Default
             Created: 19 February 2014 06:58 PM
             Updated: 31 October 2015 10:12 AM



SNSMO seemed to work, but as of 2015oct30,  something still doesn't work right with coherent smoothing of multiple IFs in SNSMO for VLMB and VLDE.  SNSMO still seems to break the coherency both across IFs and between R and L.

The phase-difference between two IFs (for SN tables from FRING w/ APARM(5)=1) should just be equal to Delay*[freq_diff].  This is true for the solutions from FRING, but no longer true after SNSMO.  SNSMO also introduces R-L phase differences where there were none.

I attach some plots made with SNPLT of SN tables before and after SNSMO with VLDE and VLMB.  In both cases I used SAMPTY 'GAUS'; DOBLANK 0; REFANT 4;
BPARM 3 3 3 3 3 1 1 1 1 1; BIF 1; EIF 8; INVER 8 in SNSMO.

RL_phase.jpg:  R-L diff in SN-table phase vs. time, all plotted from +180 to -180degs
 yellow: pre-smooth, R+L SN-table phases track very well
 green:  VLDE smooth (GAU; FWHM=1hr): R-L phase-wraps introduced
 pink:   VLMB smooth (GAU; FWHM=1hr):  "     "              "

delay+phase_pre_smooth.jpg:
  green:  phase diff IF1-IF8, from -180 to +180degs
  yellow: delay, range = +-2.232nanosecs
  =>  delay tracks IF1-IF8 phase diff (they are opposite
     signs, so should be "mirror image")

delay+phase_VLDE.jpg: 
  as above, but after VLDE smoothing: phase differences
  between IF1 and IF8 no longer correspond to delay

delay+phase_VLMB.jpg: 
  same thing for VLMB

I attach a TASAV with the relevant SN tables:
SN 8:  before smoothing
SN 9:  SNSMO VLDE
SN 10: SNSMO VLMB


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