[daip] [!5297]: aips - list fringes snr

[Eric Greisen]

Eric Greisen updated #5297
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                 Due: - Cleared - (was: 29 October 2014 05:30 PM)

list fringes snr
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           Ticket ID: 5297
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/5297
           Full Name: Gisela Ortiz
               Email: g.ortiz at crya.unam.mx
             Creator: User
          Department: AIPS Data Processing
       Staff (Owner): Eric Greisen
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template Group: Default
             Created: 01 August 2014 06:24 PM
             Updated: 27 October 2014 07:09 PM
      Resolution Due: 04 November 2014 05:30 PM (7d 22h 20m)



Your interpretation of the output from is correct.  However, one
does have to be careful interpreting it.  Normally VLBA data
have multiple spectral channels and even IFs.  The rms is the
rms in the single-channel values, not in some average over
time and channel.  POSSM will show the scan average profile
and that will contain time averaged amplitudes and phases.
Note that phase is what you should look at - of the spectrum
of phase is not randomly scattered from -180 to +180, then
you are seeing fringes in the scan average spectrum.  The
expected amplitude in the absence of any signal is still one
sigma, so don't be fooled by the presence of amplitude.

I do not know how you are looking at "fringe rate" which is the
rate of change of the phase with time.  The correlator takes out
almost all of this leaving only a residual phase.  If that is changing
with time then scan averages might well reduce the average
signal even to nearly zero despite strong signals.

In summary, your SNR = 0.26 means that the noise in one time
sample in one spectral channel is 4 times the signal.  Fortunately
you get to average channels and times.

Eric Greisen
 



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