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Timing calibration and spectral cleaning of LOFAR time series data
Radboud University Nijmegen, The Netherlands.
Vrije Universiteit Brussel, Belgium.
Radboud University Nijmegen, The Netherlands.
Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands ; Netherlands Institute for Radio Astronomy, The Netherlands ; Max Planck Institute for Radio Astronomy, Germany.
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2016 (English)Manuscript (preprint) (Other (popular science, discussion, etc.))
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Text
Abstract [en]

We describe a method for spectral cleaning and timing calibration of short voltage time series data from individual radio interferometer receivers. It makes use of the phase differences in Fast Fourier Transform (FFT) spectra across antenna pairs. For strong, localized terrestrial sources these are stable over time, while being approximately uniform-random for a sum over many sources or for noise. Using only milliseconds-long datasets, the method finds the strongest interfering transmitters, a first-order solution for relative timing calibrations, and faulty data channels. No knowledge of gain response or quiescent noise levels of the receivers is required. With relatively small data volumes, this approach is suitable for use in an online system monitoring setup for interferometric arrays. We have applied the method to our cosmic-ray data collection, a collection of measurements of short pulses from extensive air showers, recorded by the LOFAR radio telescope. Per air shower, we have collected 2 ms of raw time series data for each receiver. The spectral cleaning has a calculated optimal sensitivity corresponding to a power signal-to-noise ratio of 0.08 (or -11 dB) in a spectral window of 25 kHz, for 2 ms of data in 48 antennas. This is well sufficient for our application. Timing calibration across individual antenna pairs has been performed at 0.4 ns precision; for calibration of signal clocks across stations of 48 antennas the precision is 0.1 ns. Monitoring differences in timing calibration per antenna pair over the course of the period 2011 to 2015 shows a precision of 0.08 ns, which is useful for monitoring and correcting drifts in signal path synchronizations. A cross-check method for timing calibration is presented, using a pulse transmitter carried by a drone flying over the array. Timing precision is similar, 0.3 ns.

Place, publisher, year, edition, pages
2016.
Keyword [en]
Astrophysics - Instrumentation and Methods for Astrophysics
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
URN: urn:nbn:se:lnu:diva-51520DOI: 10.1051/0004-6361/201527809OAI: oai:DiVA.org:lnu-51520DiVA: diva2:915284
Available from: 2016-03-29 Created: 2016-03-29 Last updated: 2017-03-31

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Thoudam, Satyendra
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CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf