1 / 11

RFI Flagging in the LOFAR Imaging Pipeline

RFI Flagging in the LOFAR Imaging Pipeline. David Rafferty and the Flagging Team. Some Typical RFI. LBA data (SB64 of L2009_14319): No flagging or squashing. HBA data (SB48 of L2009_16167): No flagging or squashing. Current Flagging Scheme.

loring
Download Presentation

RFI Flagging in the LOFAR Imaging Pipeline

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. RFI Flagging in the LOFAR Imaging Pipeline David Rafferty and the Flagging Team

  2. Some Typical RFI LBA data (SB64 of L2009_14319): No flagging or squashing HBA data (SB48 of L2009_16167): No flagging or squashing

  3. Current Flagging Scheme • To date, best results achieved using the MAD (Median Absolute Deviation) Flagger: • First, run on unsquashed data with a medium frequency window and small time window • Next, run repeatedly on squashed data with a wide time window to catch broad-band RFI • Runs in ~ ½ real time for 20-station data (e.g., 1 hour for a 2-hour dataset)

  4. LBA Data after MADFlagger SB57 of L2009_14319 SB72 of L2009_14319

  5. HBA Data after MADFlagger SB38 of L2009_16167

  6. NDPPP • New version of DPPP by Ger van Diepen • Many improvements and new features, but those most relevant to RFI flagging include: • Significantly faster than IDPPP • Ability to flag on any combination of polarizations • New PreFlagger allows flagging of individual channels, baselines, etc. • Many more flagging strategies are now practical

  7. Example NDPPP Run • 2 passes on unsquashed data using XX and YY only: • Freq. window = 101 channels, time window = 1 • Freq. window = 1, time window = 101 time slots • 1 pass on squashed data using all polarizations with wide time window • Runs in ~ ¼ real time for 20-station data (e.g., 30 min on a 2-hour dataset), IDPPP requires > real time

  8. Example NDPPP Run on HBA Data SB50 of L2009_16167

  9. Example NDPPP Run on HBA Data SB50 of L2009_16167

  10. Flagger of André Offringa • Not yet part of DPPP • Run with command “rficonsole <input.ms>” • “Best” strategy appears to work very well • Runs at 1/2 real time for 20-station data • 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

  11. Summary • NDPPP allows for many more practical flagging schemes – these need testing • Need strategy to deal with broad-band, long-duration RFI (i.e., wider than ~ half the flagging window) • Need a thorough characterization of the typical RFI seen in LBA and HBA • Further extend DPPP flagging capabilities

More Related