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Basic Information on closure
Purpose: Plot closure quantities
Categories: uv analysis, plotting
CLOSURE is a Miriad task that plots closure quantities: the
closure phase ("triple phase"), closure amplitude ("quad
amplitude"), and two less well known quantities - the triple
amplitude and quad phase.
These are defined as
Closure (triple) phase: arg( V12*V23*conjg(V13) )
Closure (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
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
Standard visibility linetype. See the help line for more
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
Task enrichment parameters. Several parameters can be given,
separated by commas. Minimum match is supported. Possible
amplitude Plot the amplitude quantity (the default is to plot
quad Plot the quad quantity (the default is to plot the
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.
log Make a log file closure_log.txt.
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
nocal Do not perform gain calibration.
nopol Do not perform polarisation calibration on the data.
nopass Do not perform bandpass calibration on the data.
Revision: 1.8, 2013/08/30 01:49:21 UTC
Generated by email@example.com on 21 Jun 2016