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