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CIRA-Pulsars-and-Transients-Group / vcsbeam

Beamforms MWA-VCS data
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psrfits made by vcsbeam is affected more by RFI compared with vcstools #65

Open mengyaoxue opened 2 days ago

mengyaoxue commented 2 days ago

When I beamform toward the same pointing position using the same (legacy) data, the psrfits data products made by vcstools have higher quality compared with the psrfits made by vcsbeam (pulsars detections have higher presto sigma folded with the same ephemeris). According to the example below, it seems that vcsbeam is affected more by RFI compared with vcstools. Not sure if that is because of the definition of 'scale' in https://github.com/CIRA-Pulsars-and-Transients-Group/vcsbeam/blob/6fcc7e461053538ae79cb8fc648b6da59f52e89d/src/form_beam.cpp#L437 compare

robotopia commented 2 days ago

I think you are correct, @mengyaoxue . There is definitely a difference between the way the output values are clipped and scaled in VCSTools vs VCSBeam. If memory serves, in VCSTools, the max and min are set differently, possibly based on the standard deviation of the values (within a 1-second time frame), and as a result, abnormally large values get clipped. VCSBeam's output is "closer to the truth", which unfortunately means (impulsive) RFI is also more "truthfully" represented.

It might be worth adding an extra option to the beamformer to let the user decide on which strategy should be used for setting the max and min. It would be an easy way to mitigate strong RFI, but should only be used if the pulsar signal itself would not also get clipped. The max and min decision is made on a per (fine) channel basis.