Calibration Smoothing (smoothcal)

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4.5.4 Calibration Smoothing (smoothcal)

The smoothcal task will smooth calibration solutions (most usefully G or T) over a longer time interval to reduce noise and outliers. The inputs are:

#  smoothcal :: Smooth calibration solution(s) derived from one or more sources:

vis          =         ’’   #  Name of input visibility file
tablein      =         ’’   #  Input calibration table
caltable     =         ’’   #  Output calibration table
field        =         ’’   #  Field name list
smoothtype   =   ’median’   #  Smoothing filter to use
smoothtime   =       60.0   #  Smoothing time (sec)
async        =      False   #  if True run in the background, prompt is freed

The smoothing will use the smoothtime and smoothtype parameters to determine the new data points which will replace the previous points on the same time sampling grid as for the tablein solutions. The currently supported smoothtype options:

’mean’ — use the mean of the points within the window defined by smoothtime (a “boxcar” average),
’median’ — use the median of the points within the window defined by smoothtime (most useful when many points lie in the interval).

Note that smoothtime defines the width of the time window that is used for the smoothing.

ALERT: Note that smoothcal currently smooths by field and spw, and thus you cannot smooth solutions from different sources or bands together into one solution.

Figure 4.8: The ’amp’ of gain solutions for NGC4826 before (top) and after (bottom) smoothing with a 7200 sec smoothtime and smoothtype=’mean’. Note that the first solution is in a different spw and on a different source, and is not smoothed together with the subsequent solutions.

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An example using the smoothcal task to smooth an existing table:

smoothcal(’n4826_16apr.ms’,
       tablein=’n4826_16apr.gcal’,
       caltable=’n4826_16apr.smoothcal’,
       smoothtime=7200.,
       smoothtype=’mean’)

# Plot up before and after tables
plotcal(’n4826_16apr.gcal’,’’,’amp’,antenna=’1’,subplot=211)
plotcal(’n4826_16apr.smoothcal’,’’,’amp’,antenna=’1’,subplot=212)

This example uses 2 hours (7200 sec) for the smoothing time and smoothtype=’mean’. The plotcal results are shown in Figure 4.8.

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