Extend

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3.4.2.9 Extend

mode                =   ’extend’        #  Flagging mode (list/manual/clip/shadow/quack/
                                        #   elevation/tfcrop/rflag/extend/unflag/summary
                                        #   )
...
     ntime          =     ’scan’        #  Time-range to use for each chunk (in seconds
                                        #   or minutes)
     combinescans   =      False        #  Accumulate data across scans.
     extendpols     =       True        #  If any correlation is flagged, flag all
                                        #   correlations
     growtime       =       90.0        #  Flag all ’ntime’ integrations if more than X%
                                        #   of the timerange is flagged (0-100)
     growfreq       =       90.0        #  Flag all selected channels if more than X% of
                                        #   the frequency range is flagged(0-100)
     growaround     =      False        #  Flag data based on surrounding flags
     flagneartime   =      False        #  Flag one timestep before and after a flagged
                                        #   one (True/False)
     flagnearfreq   =      False        #  Flag one channel before and after a flagged
                                        #   one (True/False)

The extend mode may be most useful after running the tfcrop or rflag autoflagging procedures. Sometimes, these algorithms leave small islands of unflagged data behind, data that are surrounded by flagged visibilities in the time-frequency space. Although the algorithm may deem these visibilities as good ones, they are frequently affected by low-level RFI that spills from the adjacent, flagged points and one may wish to clean those up.

ntime specifies the time ranges over which to clean up, e.g. ’1.5min’ or ’scan’ which checks on all data within a scan. To span time ranges larger than scans, one can set combinescans to True.

extendpols=True would extend all flags to all polarization products when at least one of them is flagged.

growtime flags the entire time range for a flagged channel, when a certain fraction of flagged time intervals is exceeded.

growfreq is similar but extends the flags in frequency when a given fraction of channels is already flagged.

growaround checks for flagged data points in the time-frequency domain that neighbor a datum. The threshold is four data points. If more surrounding points are flagged, the central datum will be flagged, too.

flagneartime flags adjacent data points along the time axis, around a flagged datum

flagnearfreq flags neighboring channels.

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