RFI Flagging in the Imaging Pipeline
Some Typical RFISB64 of L2009_14319:No flagging or squashing
SB64 of L2009_14319:Averaged in frequency,
but no flagging
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
LBA Data after MADFlagger
SB64 of L2009_14319
AfterBefore
HBA Data after MADFlagger
135 Mhz HBA data of Cygnus A (L2009_16007)
Flagger of André Offringa
• Not yet part of DPPP– Run with command “rficonsole <input.ms>”
• 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 don’t meet flagging
criteria on their own but do when summed
LBA Data after rficonsole
SB64 of L2009_14319
Before AfterrficonsoleMADFlagger
Broad-band, Long-duration RFI
MADFlagger 4 Offringa’s flagger
SB72 of L2009_14319
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