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VLBI Phase Correction with Effelsberg WVR

VLBI Phase Correction with Effelsberg WVR. A. Roy U. Teuber H. Rottmann R. Keller. Troposphere Seen by VLBI at 86 GHz. The Scanning 18-26 GHz WVR for Effelsberg. March 16th, 2004. The Scanning 18-26 GHz WVR for Effelsberg. Front-end opened. Typical Water Line Spectrum.

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VLBI Phase Correction with Effelsberg WVR

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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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