[daip] [!5764]: aips - SNSMO with mode "VLMB" sometimes breaks the relationship between phase(per IF) and delay

[Eric Greisen]

Eric Greisen updated #5764
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              Status: Closed (was: Open)
                 Due: - Cleared - (was: 05 March 2015 05:18 PM)

SNSMO with mode "VLMB" sometimes breaks the relationship between phase(per IF) and delay
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           Ticket ID: 5764
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/5764
           Full Name: Michael Bietenholz
               Email: mbieten at yorku.ca
             Creator: User
          Department: AIPS Data Processing
       Staff (Owner): Eric Greisen
                Type: Issue
              Status: Closed
            Priority: Default
      Template Group: Default
             Created: 11 November 2014 03:35 PM
             Updated: 03 March 2015 06:29 PM



If you do not smooth delay and mbdly then the correction of phases
by delay replicates what FRING did to the phases in the first place.
If you do smooth delay, then you correct phases by the smoothed delay
and then in VLMB average up all phases (which now contain some delay correction
due to the difference between the smoothed delay and the one
FRING used).  Then the average is smoothed phases are re-corrected by
the smoothed delay - but the average phase was not right to start with.
If smoothing of delay makes big changes then this can be a serious thing.
VLDE does the right thing - phases in IFs 2-N are the phase in IF 1 plus a
delay correcion.  VLDE smooths the delays and phases of IF 1 and then
recomputes the phases of IFs 2-N as P(1) + Dnu(i)*D(1).  I hesitated to
remove or replace VLMB since it has been there a long time but I think it
is wrong.

Eric




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