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Do we need WVRs for geodetic VLBI?

Do we need WVRs for geodetic VLBI?. Joerg Wresnik (1) , Johannes Boehm (1) , Harald Schuh (1) , Arthur Niell (2). (1) Institute of Geodesy and Geophysics (IGG), TU Vienna, Austria (2) MIT Haystack Observatory, MA, USA. Workshop on Measurement of Atmospheric Water Vapour:

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Do we need WVRs for geodetic VLBI?

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  1. Do we need WVRs for geodetic VLBI? Joerg Wresnik (1), Johannes Boehm (1), Harald Schuh (1), Arthur Niell (2) (1) Institute of Geodesy and Geophysics (IGG), TU Vienna, Austria (2) MIT Haystack Observatory, MA, USA Workshop on Measurement of Atmospheric Water Vapour: Theory, Techniques, Astronomical and Geodetic Applications Wettzell / Hoellenstein (Germany), October 9-11, 2006

  2. VLBI 2010 Working Group 3 of IVS (2004-2005) Tasks: Current and Future Requirements for Geodetic VLBI Systems Goals: • accuracy of 1mm site position & of 1mm/year velocity • continuous measurements for EOP • rapid generation & distribution of IVS products Design a new VLBI observing system based on small antennas with 1mm accuracy - number, location and configuration of antennas System studies and simulations

  3. Monte Carlo simulation wzd & clocks are stochastic processes simulate for station 1 and 2 τ 90-e atmosphere 1 clocks 2

  4. Simulation of wzd and clock parameters Simulate the wet zenith delay random walk variances of: 0.1 psec²/s 0.7 psec²/s

  5. Simulation of wzd and clock parameters Simulate the clocks • random walk • Allan standard deviation of: 2∙10-15@15min • 1∙10-14@50min

  6. Simulation of wzd and clock parameters Simulate observation errors • white noise: 4 psec • 8 psec • 16 psec

  7. Simulation of wzd and clock parameters simulation of 25 identical 24 hour sessions simulate wzd 25 times for each station generate white noise 25 times for each station 0.1 psec**2/sec 0.7 psec**2/sec 4 psec simulate clocks 25 times for each station 8 psec 16 psec 2e-15@15min 1e-14@50min What are the effects of wzd and clocks? Does a “4psec antenna” improve the results?

  8. Obs. Schedule: fast antennas The schedule was created by Anthony Searle and Bill Petrachenko

  9. Obs. Schedule: high observation density • 16 stations • 120 baselines • 100 scans/hour/station • Antenna specification • using 16 antennas with the same size as • Algonquin but with faster slewing rates • azimuth max slewing rate of 18 deg/s • azimuth max acceleration of 3.6 deg/s² • elevation max slewing rate of 4.5 deg/s • elevation max acceleration of 0.9 deg/s² • data rate of 48 Gb/s. 5760 scans 116308 observations • Scan length • 5 sec every 30 sec • Source catalogue • 50 sources

  10. Baseline lengths repeatability wet zenith delay 0.1 psec**2/sec 0.7 psec**2/sec clocks 2e-15@15min (ASD) 0.0036 psec**2/sec (PSD) white noise 4 psec 16 psec • if the PSD of wet zenith delay is 0.7 psec**2/sec, 4 psec antennas give the same result as 16 psec antennas by PSD of wet zenithdelay of 0.1 psec**2/s • the wet zenith delay is the limiting factor

  11. Conclusions and outlook Largest PSD values for wet zenith delay – lowest PSD values for clocks: • PSD of wet zenith delays dominates the baseline length repeatability • hardly any difference between ‘4, 8 and 16 psec antennas' WVR could improve geodetic VLBI Next steps Simulation for wzd • station dependence • elevation and azimuth dependence

  12. Thanks for your attention

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