RFI Flagging in the Imaging Pipeline

1. RFI Flagging in the Imaging Pipeline

2. Some Typical RFI SB64 of L2009_14319: No flagging or squashing SB64 of L2009_14319: Averaged in frequency, but no flagging

3. 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

4. LBA Data after MADFlagger Before After SB64 of L2009_14319

5. HBA Data after MADFlagger 135 Mhz HBA data of Cygnus A (L2009_16007)

6. 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

7. LBA Data after rficonsole MADFlagger Before rficonsole After SB64 of L2009_14319

8. Broad-band, Long-duration RFI MADFlagger  4 Offringa’s flagger SB72 of L2009_14319

9. 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