Content-type: text/html Manpage of closure


Section: User Commands (1)
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uv analysis, plotting  


CLOSURE is a Miriad task which plots some closure quantities. The these include the closure phase (the "triple phase"), the closure amplitude (the "quad amplitude"), and two less well known quantities -- the triple amplitude and quad phase.

These are gefined as

  Closure phase     (triple phase):   arg( V12*V23*conjg(V13) )
  Closure amplitude (quad amplitude): abs( (V12*V34)/(V14*conjg(V34)) )
  Triple amplitude:                   abs( V12*V23*conjg(V13) )**0.3333
  Quad phase:                         arg( (V12*V34)/(V14*conjg(V34)) )

The closure phase, quad phase and closure amplitude should be independent of antenna-based errors, and for a point source should have values of zero phase or unit amplitude. The triple amplitude is independent of antenna-based phase errors (but not amplitude errors), and for a point source is a measure of the flux density.

The task works by averaging the quantites that are the argument of the abs or arg function. These are always averaged over the selected frequency channels and over the parallel-hand polarizations. Optionally the averaging can also be done over time and over the different closure paths.

CLOSURE also prints (and optionally plots) the theoretical error (as a result of thermal noise) of the quantities. Note this assumes a point source model, and that the signal-to-noise ratio is appreciable (at least 10) in each averaged product.  


The input visibility datasets. Several datasets can be given.
Standard visibility selection. See help on "select" for more information.
Standard visibility linetype. See the help "line" for more information.
Normal Stokes/polaization selection. The default is to process all parallel-hand polarisations.
PGPLOT plotting device. The default is no plotting device (the program merely prints out some statistics).
The number of plots per page in x and y. The default depends on the number of plots.
The y range of the plots. The default is to autoscale.
Time averaging interval. The default is no time averaging of the triple correlations.
Task enrichment parameters. Several parameters can be given, separated by commas. Minimum match is supported. Possible options are:
  amplitude Plot the amplitude quantity (the default is to plot phase).
  quad      Plot the quad quantity (the default is to plot the
            triple quantity).
  avall     Average all quantities from different triangles
            together. Note the theoretical error estimates are
            incorrect when using options=avall.
  notriple  Plot data from all quantities on a single plot.
  rms       Plot theoretical error bars on the points. The error
            bars are +/- sigma.
The following give control over calibration to be applied to the visibility data before the triple correlations are formed. Note that applying phase calibrations does not affect the closure phase!
  nocal     Do not perform gain calibration.
  nopol     Do not perform polarisation calibration on the data.
  nopass    Do not perform bandpass calibration on the data.




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Time: 18:35:38 GMT, July 05, 2011