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Effelsberg WVR for VLBI Phase Correction: Performance & Future Enhancements

This study focuses on the phase correction using the Effelsberg Water Vapor Radiometer (WVR) for VLBI observations. It details the requirements for phase correction, opacity measurements, and calibration accuracy. Results show improved coherence and signal-to-noise ratio after correction. Future enhancements include cloud removal and hardware improvements for better efficiency and accuracy.

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Effelsberg WVR for VLBI Phase Correction: Performance & Future Enhancements

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  1. VLBI Phase Correction with Effelsberg WVR A. Roy U. Teuber H. Rottmann R. Keller

  2. Troposphere Seen by VLBI at 86 GHz

  3. The Scanning 18-26 GHz WVR for Effelsberg March 16th, 2004

  4. The Scanning 18-26 GHz WVR for Effelsberg Front-end opened

  5. Typical Water Line Spectrum

  6. WVR Performance Requirements Phase Correction Aim: coherence = 0.9 requires   / 20 (0.18 mm rms) after correction Need: thermal noise  14 mK in 3 s Measured: 12 mK Need: gain stability 3.9 x 10-4 in 300 s Measured: 2.7 x 10-4 Opacity Measurement Aim: correct visibility amplitude to 1 % (1 ) Need: thermal noise  2.7 K Measured: 12 mK Need: absolute calibration  14 % (1 ) Measured: 5 %

  7. WVR Path Data from 3 mm VLBI, April 2004

  8. VLBI Phase Correction Demo NRAO 150 Pico Veleta - Effelsberg 86 GHz VLBI 2004 April 17 No phase correction VLBI phase WVR phase EB phase correction path 3.4 mm Coherence function before & after EB+PV phase correction ● Path rms reduced 1.0 mm to 0.34 mm ● Coherent SNR rose 2.1 x 420 s

  9. VLBI Phase Correction Demo NRAO 150 Pico Veleta - Effelsberg 86 GHz VLBI 2004 April 17 Before phase correction at EB VLBI phase WVR phase After phase correction at EB path 3.4 mm Coherence function before & after ● Path rms reduced 0.85 mm to 0.57 mm ● Coherent SNR rose 1.7 x 420 s

  10. VLBI Phase Correction Demo NRAO 150 Pico Veleta - Effelsberg 86 GHz VLBI 2004 April 17 Before phase correction at EB VLBI phase WVR phase After phase correction at EB path 3.4 mm Coherence function before & after ● Path rms saturated at 0.95 mm ● Coherent SNR decrease 7.5 x 420 s

  11. VLBI Phase Correction Demo Coherence function after phase correction at EB divided by CF before phase correction NRAO 150 Pico Veleta - Effelsberg 86 GHz VLBI 2004 April 17 ● Coherence improves for most scans

  12. Cloud Removal EB WVR path time series Keep VLBI scan times only Subtract linear rate ● Cloud contamination shows up as large scatter in the path lengths NRAO 150 86 GHz VLBI 2004 April 17

  13. Validation of Opacity Measurement

  14. Absolute Calibration for Astrometry & Geodesy

  15. WVR Comparison at Effelsberg July 12th, 2005

  16. Conclusion ● Effelsberg has a WVR ● Phase correction of 3 mm VLBI improves coherence ● Opacity measurements are reliable ●Absolute calibration agrees within 5 % with GPS and radiosonde ●Ready for friendly users Future ●Connect to EVN calibration pipeline and streamline AIPS import ● Improve cloud separation & line fitting algorithm ● Hardware: improve temperature stabilization reduce spillover with new feed? improve integration time efficiency better beam overlap: move to prime focus receiver boxes http://www.mpifr-bonn.mpg.de/staff/aroy/wvr.html

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