VLBI experiment vt14a

The goal of the expriment

Determine positions of two new stations ASKAP-07 and WARKWORT that never before paricipated in a geodetic-style VLBI experiments. More datails can be found here.

Main Result

Position at epoch 2010.05.07: 
    ASKAP-07    
             X -2556743707 -+ 193 mm            
             Y  5097440315 -+ 326 mm            
             Z -2847749657 -+ 223 mm

             Error ellipse:

             U Comp        -+ 424 mm
             E Comp        -+ 109 mm
             N Comp        -+  75 mm

    WARKWORT 
             X -5115325540 -+ 141 mm 
             Y   477844424 -+  71 mm             
             Z -3767193985 -+ 122 mm

             Error ellipse:

             U Comp        -+ 184 mm
             E Comp        -+  64 mm
             N Comp        -+  41 mm

Other results

ATCA participated as a phased array. To our surprise, position of the ATCA phase reference center was not ATCA-104 as we anticipated, but a point with pad CATN5 that according to L. Petrov, C. Phillips, A. Bertarini, A. Deller, S. Pogrebenko, A. Mujunen, "The use of the Long Baseline Array in Australia for precise geodesy and absolute astrometry", Publications of the Astronomical Society of Australia, 26(1), 75-84, 2009. DOI: 10.1071/AS08030 has the following offset wrt ATCA-104: -30.612 m east and 76.531 m north. 
    ATCAPN5  
             X -4751639558 -+ 134 mm
             Y  2791700335 -+  83 mm
             Z -3200491045 -+ 107 mm

             Error ellipse:

             U Comp       -269 -+ 182 mm
             E Comp       -105 -+  38 mm
             N Comp        -34 -+  40 mm
Position of ATCAPN5 turned out within of 2.5 σ with respect to the position of CATN5 pad. This provides a check of accuracy of ASKAP-07 and WARKWORT stations.

Listing of the stand-alone solution at LL polarization can be found here.

Final solution was made in a global mode using all available VLBI observations plus vt14a. RR and LL band group delay were processed separately, i.e. were averaged incoherently. Troposphere path delay was computed by numerical integration of the 4D refractivity field from the MERRA numerical weather model. Ionosphere contribution was computed using ionosphere TEC maps from CODE.

Problems

  1. Polarization leakage. I made an attempt to make RR+LL combined fringe fitting solution. This helped to improve SNR at many baselines, but made more harm at another baselines, for example at baselines with WARKWORT.

  2. Autocorrelation

  3. Non-linear shape of cross-spectrum

  4. Instable phase at ASKAP-07. Fringe phase at baselines with ASKAP-07 was instable: fringe phase at ASKAP-07/PARKES, compare with fringe phase at HOBART26/PARKES.

  5. Bizarre jitter in cross-spectrum at baselines with ATCAPN5 at RR.

    6. I have no clue what is the cause of the amplitude jitter. My first guess was that there is a harmonic process with the frequency close to the Nyquist. Refringing with higher spectral resolution should show it cleanly. Instead, increasing the frequency resolution by a factor of 8 showed another jitter, which does not look like as a noise process. This is ATCAPN5 specific and it appears only at RCP.

  6. Clock break at HOBART26 at -21.2 ns at 01:36.

  7. Huge quadratic term in clock function at ASKAP-07, that changed around 01:00 as it seen from this plot. Does ASKAP-07 have a good H-maser? Clock function of WARKWORT does not show anomalies.

Conclusion

In general, I consider this experiment as successful. Error bar of position of new stations is 5–10 cm for horizontal coordinates and 20–40 cm. It is about what one might expect from a 6 hours, 1 channel, L-band experiment with two new stations.
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This page was prepared by Leonid Petrov ()
Last update: 2010.09.27_22:17:32