RFI Flagging in the Imaging Pipeline

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RFI Flagging in the Imaging Pipeline
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Some Typical RFI
SB64 of L2009_14319 No flagging or squashing
SB64 of L2009_14319 Averaged in frequency, but
no flagging
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Flagging in DPPP

• Four flaggers currently implemented in DPPP
• Complex Median and Complex Median 2 Flaggers
• Frequency Flagger
• MAD (Median Absolute Deviation) Flagger
• To date, best results achieved using the MAD
  Flagger
• First, run on unsquashed data with a wide
  frequency window and small time window
• Next, run repeatedly on squashed data with a wide
  time window

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LBA Data after MADFlagger
After
Before
SB64 of L2009_14319
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HBA Data after MADFlagger
135 Mhz HBA data of Cygnus A (L2009_16007)
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Flagger of André Offringa

• Not yet part of DPPP
• Run with command rficonsole ltinput.msgt
• Default parameters appear to work well
• Requires about the same time to run as the
  MADFlagger
• But, has two main advantages over the MADFlagger
• Uses a more sophisticated fit to visibilities
• Flags neighboring point that dont meet flagging
  criteria on their own but do when summed

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LBA Data after rficonsole
Before
After
rficonsole
MADFlagger
SB64 of L2009_14319
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Broad-band, Long-duration RFI
MADFlagger ? 4
Offringas flagger
SB72 of L2009_14319
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Future

• Flagger developed by Bas van der Tol
• Should be useful in identifying low-level RFI
  that affects more than one antenna
• Presently in testing and development
• Need strategy to deal with comb RFI and
  broad-band, long-duration RFI
• Need a thorough characterization of typical RFI