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Deep wide field VLBI imaging - “The need for speed”

Deep wide field VLBI imaging - “The need for speed”. Harro Verkouter Joint Institute for VLBI in Europe. Information content. VLBI datasets contain much more information than is extracted. Information content. Usually a field of 50x50 synthesized beams is imaged

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Deep wide field VLBI imaging - “The need for speed”

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  1. Deep wide field VLBI imaging-“The need for speed” Harro Verkouter Joint Institute for VLBI in Europe

  2. Information content • VLBI datasets contain much more information than is extracted need for speed [URSI XXVII GA - Maastricht]

  3. Information content • Usually a field of 50x50 synthesized beams is imaged • Still only 0.1% of information! • Typically corresponds with a field-of-view of 1” x 1” • Primary beam of Effelsbergis  6’ (@18cm) need for speed [URSI XXVII GA - Maastricht]

  4. Field of view limitations • Pre-correlation • Sensitivity need for speed [URSI XXVII GA - Maastricht]

  5. need for speed [URSI XXVII GA - Maastricht]

  6. Field of view limitations • Pre-correlation • Sensitivity • Post-correlation • Time smearing • Spectral resolution need for speed [URSI XXVII GA - Maastricht]

  7. need for speed [URSI XXVII GA - Maastricht]

  8. Field of view limitations(2) • VLBI datasets >> connected element array datasets • Almost obsessive need for averaging to make datasets manageable • Time smearing/spectral smearing scale with baseline length! need for speed [URSI XXVII GA - Maastricht]

  9. What can we do about it? • Pre-correlation: • EVN: actively support development for more sensitivy, e.g. PCEVN, MarkV. • EVN: 12hrs @512Mbit  10Jy/beam • Post-correlation: a lot more! • Decrease correlator integration time • Increase spectral resolution Need enhanced output data rate! need for speed [URSI XXVII GA - Maastricht]

  10. And there’s more… Once the data is correlated, is that it? • ‘re-correlate’ by mathematics; produce multiple phasecentres • Experiment with the data: apply algorithms at will • Helps with near real time space VLBI • Apply filters before exporting to user need for speed [URSI XXVII GA - Maastricht]

  11. And there’s more (2) Applicability of the algorithms is limited by the aforementioned time- and bandwidth smearing Need enhanced output datarate! need for speed [URSI XXVII GA - Maastricht]

  12. Requirements Want to map out considerable fraction of Ef primary beam (6’ @18cm): • Field-of-view of 1’x1’ needs • Integration time 0.25s • 62kHz channelwidth  2k channels for 64MHz bandwidth • Integration time ~ 1/ • Channelwidth of 62kHz remains need for speed [URSI XXVII GA - Maastricht]

  13. need for speed [URSI XXVII GA - Maastricht]

  14. need for speed [URSI XXVII GA - Maastricht]

  15. EVN MkIV Correlator limits • Integration time • Cycle time of 0.015s (actually, 1/64th of a second) • Spectral resolution • 131072 complex lags per readout = 65536 spectral points per readout • Divided over 32 products leads to 2048 spectral channels per product need for speed [URSI XXVII GA - Maastricht]

  16. Datarate • Each lag occupies 5 bytes of data (4 data+1 overhead) • Hence, ¼ million lags at 64 readouts/second equals 16Mlags/second • Which works out to be 160MByte/s need for speed [URSI XXVII GA - Maastricht]

  17. The EVN MkIV Correlator need for speed [URSI XXVII GA - Maastricht]

  18. The PCInt project • Short for Post Correlator Integrator • We want to capture the full output of the EVN MkIV correlator to disk • Need to replace output datapath Steve ParsleyMarcel LooseHarro Verkouter need for speed [URSI XXVII GA - Maastricht]

  19. The PCInt project (2) • High speed readout of the correlator was already prepared • Via DSP powered serial port • Need hardware and software to enable this • Receiving end of serial port • Gbit ethernet for transfer from correlator rack to datacollection host • Fast disk subsystem in order to support 160MByte/s (parallel RAID arrays in a Storage Area Network) need for speed [URSI XXVII GA - Maastricht]

  20. RT System Correlator Board (x8) VME High Speed Serial C40 COMM PCI Ethernet Card 100TX 1000FX (x8) SBC (x2) Correlator rack (x4) Switch CCC DDD (xn) Fibre Channel EEE (xk) FC Switch Raid Array (xm) Current situation need for speed [URSI XXVII GA - Maastricht]

  21. RT System Correlator Board (x8) VME High Speed Serial C40 COMM PCI Ethernet Card 100TX 1000FX (x8) SBC (x2) Correlator rack (x4) Switch CCC DDD (xn) Fibre Channel EEE (xk) FC Switch Raid Array (xm) Phase 0 need for speed [URSI XXVII GA - Maastricht]

  22. RT System Correlator Board (x8) VME High Speed Serial C40 COMM PCI Ethernet Card 100TX 1000FX (x8) SBC (x2) Correlator rack (x4) Switch CCC DDD (xn) Fibre Channel EEE (xk) FC Switch Raid Array (xm) Phase 1 need for speed [URSI XXVII GA - Maastricht]

  23. RT System Correlator Board (x8) VME High Speed Serial C40 COMM PCI Ethernet Card 100TX 1000FX (x8) SBC (x2) Correlator rack (x4) Switch CCC DDD (xn) Fibre Channel EEE (xk) FC Switch Raid Array (xm) Phase 2 need for speed [URSI XXVII GA - Maastricht]

  24. need for speed [URSI XXVII GA - Maastricht]

  25. Post-processing issues • Data volume = huge1hour @160MByte/s equals560GBytes of data • Use a cluster of nodes • Need automated processing • Use a processing pipeline need for speed [URSI XXVII GA - Maastricht]

  26. Processing pipeline • Correlated data is saved to disk • Apply automatically • Normalization correction • Flagging • Produce dataset with requested phasecentre(s) for user • Can also apply filtering • Export to FITS need for speed [URSI XXVII GA - Maastricht]

  27. Processing pipeline (2) Use AIPS++ • JIVE data quality assessment is already done using AIPS++ • AIPS++ supports parallel processing • Export of data to user is also already done using AIPS++ need for speed [URSI XXVII GA - Maastricht]

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