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The first year of VERA geodetic experiments

The first year of VERA geodetic experiments. J IKE Takaaki, T AMURA Yoshiaki, M AMABE Seiji, and NAOJ VERA Group VERA Observatory, National Astronomical Observatory of Japan IVS GM 2006. abstract.

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The first year of VERA geodetic experiments

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  1. The first year of VERA geodetic experiments JIKE Takaaki, TAMURA Yoshiaki, MAMABE Seiji, and NAOJ VERA Group VERA Observatory, National Astronomical Observatory of Japan IVS GM 2006

  2. abstract • Main objective of VERA geodetic VLBI experiments is to monitor the motion and stability of VERA array for precise astrometry. • We started the semi-regular geodetic VLBI experiments one year ago. • We use the 1-Gbit recording system, FX-Correrator and CALC3/MSOLV software package. • From 20 experiments, we obtained the long-term averaged coordinates of VERA antenna reference points. • We also monitored the positions of VERA stations by using GPS and compared the two results.

  3. Purposes of the VERA Geodetic VLBI Experiments • VERA aims the revelation of the structure and dynamics of our Galaxy by measuring 3-D positions and motions of Galactic compact radio objects with 10 micro arc-seconds level accuracy. • To achieve such a highly accurate measurement, the geodetic VLBI observation is crucial in VERA project. • Monitoring of both the positions and their stability with high accuracy (<2mm) is the main purpose of the VERA geodetic VLBI experiments.

  4. Results of baseline lengths obtained from 04/Dec/2004 experiment The four antennas (Mizusawa, Iriki, Ogasawara and Ishigaki ) constitute the VERA network. The longest baseline is that of Mizusawa-Ishigaki, and its length is about 2300km.

  5. Three kinds of geodetic experiments in VERA Project We hold • 1. Participation to JADE(*) by GSI for connecting VERA network with the international VLBI network. • VERA internal geodetic experiment on the semi-regular basis. • Continuous GPS Observation at VERA stations for interpolating VLBI geodetic solutions and for confirming rapid variations, • (for example. co-seismic, post-seismic, etc. ) • Also, local tie vector between VLBI and GPS points are measured. • * ”JApanese Dynamic Earth observation by VLBI”

  6. Specifications of the observation, correlation & analysis system (*) Mainly caused by the interference of artificial radio waves. Antenna, I/F & back-end are shared with the VERA astrometrical observation system.

  7. Result of VERA internal geodetic VLBI experiments maintenance We started the geodetic VLBI experiment in November 2004. These experiments are held twice a month, exclusive of antenna maintenance period、 and succeed this year. The newest experiment was carried out on 07/Jan./2006. The experiments on the above graph have finished the process of the analysis.

  8. Setting of a priori physical models and estimated parameters CALC3 and MSOLV play the same role as CALC and SOLVE respectively. CALC3 Physical Models Setting ------ Celestial Ref. Frame: icrf2000 Terrestrial Ref. Frame : itrf2000 EOP(nutation, wobble, UT1): IERS C04 (daily) Zenith Atm. Pass Delay: Saastamoinen (1972) Atmosphere Mapping Function: nhmf Ocean Tide Loading: GOTIC2, naotide99b …. Etc. MSOLV Parameters Setting ------ Clock Offset and Rate： Polynomial fitting in arbitrary epochs at each station. Zenith Atmosphere Pass Delay ： at every 1 hour & at each station. Site Coordinates: XYZ at the mean epoch of the observations. • The coordinates of Mizusawa are fixed to the GSI global solution 2005 by JADE. • The coordinates of Iriki, Ogasawara and Ishigaki are estimated.

  9. Results of the analyses Iriki: X=-3521719.5926+/-0.0017m, Vx=-0.0353+/-0.0042m/y Y= 4132174.6818+/-0.0019m, Vy= 0.0023+/-0.0047m/y Z= 3336994.2426+/-0.0017m, Vz=-0.0153+/-0.0045m/y Ogasawara: X=-4491068.8212+/-0.0020m, Vx= 0.0227+/-0.0052m/y Y= 3481544.7934+/-0.0016m, Vy= 0.0133+/-0.0041m/y Z= 2887399.5814+/-0.0016m, Vz= 0.0105+/-0.0042m/y Ishigaki: X=-3263994.7279+/-0.0017m, Vx=-0.0482/+-0.0042m/y Y= 4808056.2854+/-0.0020m, Vy= 0.0206+/-0.0049m/y X= 2619949.2291+/-0.0017m, Vz=-0.0492+/-0.0041m/y Typical error ellipsoid obtained from 1 experiment. (scale=mm) We obtained long term averaged coordinates and rates of Iriki, Ogasawara and Ishigaki antenna reference points at the epoch of 2005.0 from 20 experiments data with about 2mm errors. Size of a typical error ellipsoid obtained from 1 experiment is about +/-2mm in the direction of East-West and North-South, and about +/-7 mm in the vertical direction.

  10. Comparison of baseline lengths between VLBI and GPS These are linear-fitting solutions of the baseline lengths measured by VLBI and GPS. Differences of baseline length between VLBI and GPS are about 2cm in maximum. Differences of rates between VLBI and GPS are also a few mm/yr in almost baselines. S.D. of VLBI is smaller than that of GPS in all baselines.

  11. Time series of baseline lengths obtained from VLBI and GPS Time series of the data used to linear-fitting • Length of the baselines including Ogasawara have systematic differences of 1-2cm between VLBI and GPS. It might be due to an insufficient accuracy of Ogasawara local tie vector. • By the way, L2 band receiver of Iriki GPS is not in good condition in this period. • We detected similar changes in most of results of VLBI and GPS. Motions of some baselines have non-linear signature ------ seasonal?, or acceleration? Reason of these variations have not been revealed yet.

  12. Daily results of Ogasawara-Ishigaki baseline length by GPS. This variation is seemed to harmonizes with VLBI’s. More experiments for a long term ( several years ) are needed to obtain definite conclusion about the variation of baseline lengths.

  13. Summary • VERA project started the semi-regular geodetic VLBI experiment in Nov. 2004. • 20 experiments are carried out for 1 years. • We obtained long-term averaged coordinates of VERA antenna reference point with about 2mm precision. • We detected variations of baseline lengths with about 3-5mm S.D. from 1 year VLBI data. GPS data also harmonized with these variations.

  14. There are three special notes. A summary of specification of VERA internal geodetic VLBI experiments. • 1-Gbit recording system is used regularly. • We adopt the Mitaka FX Correlator for correlation processing. • We use CALC3/MSOLV software package to estimate the geodetic parameters.

  15. In a scientific manner, -------- • Improvement and verification of geophysical models ( ex., plate motion, ocean tide loading, non-tidal ocean loading, etc. ) are considerable. • To improve the accuracy of phase-referencing astrometric results, we have to apply the most accurate geophysical models. Synthetic result of 21 wave elements (M2, S2, K1, O1, N2, P1, K2, Q1, M1, J1, OO1, 2N2, MU2, NU2, L2, T2, MTM, MF, MM, SSA & SA). Ocean tide loading deformation at Ogasawara Station predicted by GOTIC2 & NAO99b

  16. Purposes of the VERA Geodetic VLBI Experiments VERA aims the reveal the structure and dynamics of our Galaxy by measuring 3-D positions and motions of Galactic compact radio objects with 10 micro arc-seconds level accuracy.

  17. Specifications of Operation, Correlation and Analysis system VERA Back-end System VERA AOC Room MSOLV S/X Front-end The Mitaka FX Correlator VERA antenna & GPS

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