Splitting out Calibrated uv data (split)

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4.7.1 Splitting out Calibrated uv data (split)

The split task will apply calibration and output a new sub-MS containing a specified list of sources (usually a single source). The inputs are:

#  split :: Create a visibility subset from an existing visibility set:
vis          =         ’’   #  Name of input measurement set
outputvis    =         ’’   #  Name of output measurement set
datacolumn   = ’corrected’  #  Which data column(s) to split out
field        =         ’’   #  Select field using field id(s) or field name(s)
spw          =         ’’   #  Select spectral window/channels
width        =          1   #  Number of channels to average to form one output channel
antenna      =         ’’   #  Select data based on antenna/baseline
timebin      =       ’0s’   #  Value for timeaveraging
timerange    =         ’’   #  Select data based on time range
scan         =         ’’   #  Select data based on scan numbers
array        =         ’’   #  Select (sub)array by array ID number(s)
uvrange      =         ’’   #  Select data based on uv distance range
async        =      False   #  If true the taskname must be started using split(...)

Usually you will run split with datacolumn=’corrected’ as previous operations (e.g. applycal) will have placed the calibrated data in the CORRECTED_DATA column of the MS. This will produce a new MS with this corrected data in its DATA column. The modes available in datacolumn are:

   ’data’, ’model’, ’corrected’,                       # produce MS with single DATA column
   ’data,model’, ’data,corrected’, ’model,corrected’,  # pairs of columns
   ’all’                                               # all columns ’data,model,corrected’

We recommend sticking to the simple single-column modes (e.g. ’data’ or ’corrected’) or ’all’ if all columns are in the MS. Further processing may get confused by mismatched pairs of columns.

For example, to split out 46 channels (5-50) from spw 1 of our NGC5921 calibrated dataset:

split(vis=’ngc5921.usecase.ms’,
      outputvis=’ngc5921.split.ms’,
      field=’2’,                      # Output NGC5921 data (field 2)
      spw=’0:5~50’,                   # Select 46 chans from spw 0
      datacolumn=’corrected’)         # Take the calibrated data column

4.7.1.1 Averaging in split

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