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THE FIRST RESULTS OF VLBI OBSERVATIONS AT THE SVETLOE OBSERVATORY IN THE FRAMEWORK OF THE IVS OBSERVING PROGRAMS
A. FINKELSTEIN, V. GRATCHEV, A. IPATOV, Z. MALKIN, I. RAHIMOV, E. SKURIKHINA, S. SMOLENTSEV Institute of Applied Astronomy nab. Kutuzova 10, St. Petersburg 191187, Russia e-mail: amf@quasar.ipa.nw.ru

ABSTRACT. In this paper results of the first 10 geodetic VLBI sessions observed at the Svetloe
Radio Astronomical Observatory (SvRAO) of the Institute of Applied Astronomy (IAA) since March 2003 in the framework of the IVS observing programs after installation of Mark 3A terminal in cooperation with NASA. Analysis of observations has been performed at the IAA using OCCAM/GROSS software. The processing of the observations allowed us to determine with high accuracy both the coordinates of the SvRAO and Earth orientation parameters. It is also shown that including Svetloe observatory in the IVS network yields essential improvement of the accuracy of determination of the EOP. Obtained results show high quality of both observations and analysis made at the IAA.

1. INTRODUCTION
Svetloe Radio Astronomical Observatory (SvRAO) was founded by the Institute of Applied Astronomy of the Russian Academy of Sciences (IAA RAS) as the first station of the Russian VLBI network QUASAR. It is located near Svetloe village in the Karelian Neck about 100 km towards North of St.Petersburg, and is primarily intended for regular VLBI observations in the framework of domestic and international programs on astrometry, geodynamics and space geodesy (Finkelstein, 2001). Until the end of 2002 SvRAO was equipped with only terminal, Canadian S2, with Data Acquisition System developed at the IAA. Using this terminal, SvRAO participated in a number of VLBI programs in collaboration with other VLBI stations in China, Canada and Australia, also with the second IAA VLBI station, Zelenchukskaya, located in the North Caucasus. In 2002, according to the Agreement between the RAS and NASA, Mark 3A terminal was installed at SvRAO, and since 2003 the observatory started regular VLBI observations in the framework of the IVS (International VLBI Service for Geodesy and Astrometry) astrometry and geodynamics programs. Starting in the regular IVS programs is a result of nearly 15 years of efforts by the IAA, and this is a ma jor milestone for us.

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2. VLBI EQUIPMENT OF THE SVRAO
The basic instrument of the SvRAO is a new generation fully steerable radio telescope with homology backup structure. Quasi-paraboloid main dish has diameter of 32 m and focal length of 11.4 m, and the secondary mirror is an asymmetrical modified hyperboloid with the diameter of 4 m. Radio telescope has two operational slewing velocities: fast (azimuth speed 1.5 /s , elevation speed 0.8 /s) and slow (azimuth speed 1.5 /s, elevation speed 0.8 /s). Cable system provides azimuth range ±270 of North direction and elevation range (-5 -- +90 ). The radio telescope is equipped with 5 low-noise cooled receivers with HEMT amplifiers for wavelengths 1.35, 3.5, 6.0, 13 and 18/21 cm for observations in the left and right circular polarizations (Ipatov et al., 1994). To provide the low noise temperature of the "radio telescope -- radiometer" system not higher than 50­70 K some input lines of all bandwidth have to be cooled at 20 K. The micro-cryogenic closed circle refrigerators are used for the cooling of low noise amplifiers of all ranges at 20 K. To be able to switch frequency band and provide multi-band observations quasi simultaneously, the input horns for different wavelengths are located above the circle of 3-meter diameter and the fast switching is achieved by turning of the secondary mirror at certain angle around the radio telescope axis. To maintain simultaneous receiving at the S and X bands in both orthogonal polarizations (to eliminate ionosphere effects), which is essential for realization of astrometric, geodynamical and geodetic programs, the special combined horn has been constructed. The working ranges of intermediate frequencies of these cryo electronic radiometers are 130­480 MHz and 130­890 MHz for X and S bands correspondingly. The noise temperature at the input of cryostat is 15 K and total noise temperatures of "radio telescope -- radiometer" system are not higher 50 K for S band and 70 K for X band at the elevations above 20 . The signal from the radiometer output is transmitted along the phase stable coaxial lines connecting the focal cabin of radio telescope with 14-channel Mark 3A terminal located at the laboratory building. The registration is fulfilled on the magnetic tapes with the use of 24-track tape recorder Honeywell. One tape is provided the tape recording of 18-24 hours of observations depending on program. Svetloe VLBI site is provided with a qualitative system of time-frequency synchronization, consisting of 4 H-masers with long-time stability about (3 - 5) â 10-15 . One H-maser operates constantly and each other can be switched on during one hour and will achieve all nominal technical parameters during 24 hours. The synchronization of the local time scale with Universal Time is realized with the use of GPS and GLONASS receivers with the accuracy (30­50) ns. The phase calibration system -- generator of picosecond impulses includes two basic units: pulse generator of harmonics on semiconductor diode and circuit producing 1 MHz reference signal with rectangular wavefront from the harmonic signal with the frequency of 5 MHz provided by the H-maser. The measurement of the delay of 5 MHz reference signal in cable system is provided by phase comparator. Automatic meteorological data system measures atmospheric pressure, direction and velocity of wind, temperature and humidity of air. These data are recorded in log-file of the media. All systems of the radio telescope are united in general complex with the help of central computer with specialized software, permitting the automatic carrying out of observations. The basis of this software is the Mark IV Field System, Version 9.5.17, being the international standard for VLBI (Himwich, 2000). It was added by site-oriented interface for the control of dish, radiometers and radiometric registration. Software for this interface was developed in Linux media with the use of SNAP language fully integrated in FS media for VLBI and single dish modes.

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3. OBSERVATIONS AND RESULTS
The first regular IVS session at Svetloe was observed on March 6, 2003 (Finkelstein et al., 2003). To Sep 1, 2003 Svetloe participated in 14 IVS sessions -- 10 R4 sessions (determination of EOP), 3 TRF sessions (improvement of the terrestrial reference frame), 1 EURO session (investigation of crustal deformations in Europe). Four R4 sessions were not correlated in time because of delay in tape delivering due to customs problems. List of sessions and related statistics are presented in Table 1. Table 1: VLBI sessions observed at Svetloe in March­August 2003. Session code R4061 T2015 R4063 R4065 T2016 R4069 EURO68 T2017 R4073 R4075 R4079 R4081 R4083 R4085 Total Date Mar 6 Mar 18 Mar 20 Apr 3 Apr 8 Apr 29 May 6 May 20 May 29 Jun 12 Jul 10 Jul 24 Aug 7 Aug 21 Number of stations 8 7 8 8 7 8 9 8 8 5 Number of Number of sources scans 36 313 44 348 34 332 44 322 38 231 47 340 53 324 54 542 54 399 43 203 correlated without Svetlo correlated without Svetlo correlated without Svetlo correlated without Svetlo 94 3354 Number of observations 2373 2079 2902 2305 1067 2693 5433 1985 2306 658 e e e e 23801

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Schedule files for these sessions were prepared at the NASA Goddard Space Flight Center (GSFC) for the R4 program, and at the Geodetic Institute of the University of Bonn for the T2 and EURO programs. Correlation of the observations was made at the USNO correlator, except two sessions EURO68 and T2017 which was correlated at the Bonn correlator. The processing factor which is equal to ratio of correlation time to session duration was between 1.0 and 4.2 depending on quality of data and number of stations. The time delay between observations and availability of correlated data was 10­14 days for R4 sessions and 2­4 months for T2 and EURO sessions. During those 10 IVS sessions observed with the participation of SvRAO 23801 observations were obtained, 20596 of them are good, i.e. suitable for scientific analysis. These observations were obtained at 22 VLBI stations, and 113 baselines of length from 99 km (DSS65­YEBES) to 12,496 km (DSS45­YEBES). Station statistics is presented in Table 2. Scientific analysis of observations has been performed at the IAA using OCCAM/GROSS software (Malkin et al., 2000). The analysis was aimed to compute accurate coordinates of Svetloe radio telescope reference point and the EOP, in accordance with the goal of the corresponding IVS programs. A priori coordinates of the Svetloe radio telescope were obtained from the processing of the GPS observations collected at the permanent GPS station SVTL installed at Svetloe, and geodetic survey on the local geodetic network (Smolentsev et al., 2001). Geocentric coordinates of the Svetloe radio telescope reference point obtained at the IAA are presented in Table 3. Coordinates are referred to the ITRF2000 at epoch 2003.30. For this computation coordinates of all stations except Svetloe were fixed to VTRF2003 values with only exception of 3


Table 2: List of participating stations (D ­ distance from Svetloe, Nsess ­number of sessions, Nobs ­ number of observations, Ngood ­ number of good observations, Nav ­ average number of observations per session, Pg ­ percentage of good observations). Station ALGOPARK CRIMEA DSS45 DSS65 FORTLEZA GGAO7108 GILCREEK KASHIM34 KOKEE MATERA MEDICINA NOTO NYALES20 ONSALA60 SESHAN25 SVETLOE TSUKUB32 URUMQI WESTFORD WETTZELL YEBES YLOW7296 Location Canada Ukraine Australia Spain Brazil USA USA, Alaska Japan USA, Hawaii Italy Italy Italy Norway, Spitsbergen Sweden China Russia Japan China USA Germany Spain Canada D 6256 1811 11734 3192 8428 6767 5854 7174 9561 2374 2140 2809 2133 1080 6761 -- 7141 4127 6269 1655 3130 5807 Nsess 6 3 1 1 7 2 5 1 6 9 2 1 6 1 1 10 2 2 1 7 2 1 Nobs 3749 968 505 1269 2359 91 3658 608 2789 6183 2069 1420 5103 1396 569 5671 1321 1116 283 4844 1427 204 Ngood 3412 779 401 1158 2099 47 3446 513 2516 4973 1771 1227 4585 1135 492 4866 1165 823 204 4284 1100 196 Nav 569 260 401 1158 300 24 689 513 419 553 886 1227 764 1135 492 487 583 412 204 612 550 196 Pg 91.0 80.5 79.4 91.3 89.0 51.6 94.2 84.4 90.2 80.4 85.6 86.4 89.8 81.3 86.5 85.8 88.2 73.7 72.1 88.4 77.1 96.1

Table 3: Svetloe coordinates at the epoch 2003.30 aligned to ITRF2000. Analysis center IAA VTRF MAO GSFC X, m 2730173.850 ±1 .850 ±3 .838 ±2 .849 ±1 Y, m 1562442.667 ±1 .668 ±2 .670 ±1 .666 ±1 Z, m 5529969.064 ±2 .071 ±6 .070 ±3 .063 ±2

coordinates of the station Gilmore Creek which was corrected for the jump in station position due to the earthquake happened in November 2002 resulted in station displacement of about 6 cm. For comparison, coordinates given in the IVS reference system VTRF2003 (Nothnagel, 2003), and those computed at the Main Astronomical Observatory (MAO), Kiev, Ukraina (Bolotin, 2003) are also given in Table 3. New GSFC estimate of Svetloe coordinates obtained and kindly provided by Daniel MacMillan (personal communication) is also included in the Table. Solutions IAA (present work), MAO and GSFC are obtained from processing of 10­11 observ-

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ing sessions, VTRF solution is obtained by means of Helmert transformation of the GSF2002B solution (Nothnagel, 2003), which, in turn, was computed using observations of only one IVS session at Svetloe. For this reason accuracy of the VTRF coordinates of Svetloe is much worse than for other solutions. However, it is the official IVS reference frame. During the analysis we also computed baseline length for all participated stations. Of course, especially interesting for us were baselines including Svetloe station. They are shown in Table 4. Table 4: Baseline lengths (E ­ formal error, R ­ repeatability). Baseline Svetloe -- ALGOPARK CRIMEA DSS45 DSS65 FORTLEZA GGAO7108 GILCREEK KASHIM34 KOKEE MATERA MEDICINA NOTO NYALES20 ONSALA60 SESHAN25 TSUKUB32 URUMQI WESTFORD WETTZELL YEBES YLOW7296 Number of sessions 6 2 1 1 7 1 5 1 6 9 2 1 6 1 1 2 2 1 7 2 1 Length, m 6255567.6332 1810877.6189 11734020.5530 3192391.5652 8428008.6707 6767247.5654 5853689.1323 7173755.4896 9561115.4135 2373640.0976 2139526.9600 2808545.4754 2133122.9961 1079812.9364 6760938.2673 7140832.1563 4127151.1133 6269171.0929 1654774.8541 3129769.6024 5807450.7252 E, m 0.0022 0.0035 0.0169 0.0034 0.0037 0.1350 0.0021 0.0110 0.0035 0.0011 0.0024 0.0031 0.0011 0.0026 0.0103 0.0043 0.0043 0.0137 0.0010 0.0043 0.0163 R, m 0.0025 0.0049

0.0075 0.0061 0.0061 0.0019 0.0055 0.0016

0.0003 0.0018 0.0006 0.0044

It should be mentioned that in 2003 station Svetloe was included in the IVS network as tagged along station. i.e supplementary to the regular IVS R4 network. Figure 1 show a typical configuration of the R4 network in 2003. One can see that Svetloe is located near other european stations, and thus does not strengthen substantially the network geometry. So, no significant improvement of the results obtained at the R4 network can be expected after inclusion of Svetloe. Nevertheless, we tried to estimate how it influences the accuracy of EOP results (the main goal of the IVS R4 program). Estimates of pole coordinates Xp , Yp , Universal Time U T 1, and nutation angles and were computed both for whole network and for reduced network without Svetloe (Table 5). Obtained results show that inclusion Svetloe in the IVS network yields substantial improvement in quality of results. Hopefully, planned participation of Svetloe observatory in IVS programs as regular station will allow us to realize more substantial progress in the accuracy of determination of EOP and TRF, and make a valuable contribution to other geodesy and astrometry investigations.

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Figure 1: Typical network for IVS R4 experiments.

Table 5: EOP differences with the IERS C04 series (Xp , Yp -- pole coordinates, U T 1 -- Universal Time, Xc , Yc -- celestial pole offset). EOP Xp , µas Yp , µas U T 1, µs Xc , µas Yc , µas All sessions with Svetloe w/o Svetloe bias wrms bias wrms -233 127 -219 151 378 141 402 148 -79 52 -75 53 10 37 -2 69 4 76 -18 95 R4 (EOP) with Svetloe bias wrms -244 74 367 134 -87 16 16 27 -11 60 sessions w/o Svetloe bias wrms -224 92 390 134 -82 20 10 27 -29 74

Table 6: EOP formal errors (Xp , Yp -- pole coordinates, U T 1 -- Universal Time, Xc , Yc -- celestial pole offset), and other statistics (0 -- post-fit rms, Cmax -- maximum correlation between EOP). EOP (Xp ), µas (Yp ), µas (U T 1), µs (Xc ), µas (Yc ), µas 0 , ps Cmax All sessions with Svetloe w/o Svetloe 140 169 120 146 56 73 74 83 79 91 44 47 0.84 0.84 R4 (EOP) sessions with Svetloe w/o Svetloe 110 120 80 83 37 44 60 61 63 65 32 34 0.64 0.71

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4. ACKNOWLEDGMENTS
Authors wish to thank our colleagues Chopo Ma and Ed Himwich (Goddard Space Flight Center), and Brian Corey (Haystack observatory) for fruitful cooperation on VLBI technology and space geodesy being crowned with installation of Mark 3A terminal at the Svetloe observatory and its inclusion in the IVS network. We also grateful to Dan MacMillan (Goddard Space Flight Center) for providing the latest GSFC estimates of Svetloe position.

5. REFERENCES
Bolotin, S., 2003: ftp://cddisa.gsfc.nasa.gov/pub/vlbi/ivsproducts/trf/mao2003a.trf.gz Finkelstein, A. M., 2001: Radiointerferometric Network QUASAR. Science in Russia, No. 5, 20­26. Finkelstein A., A. Ipatov, S. Smolentsev, 2002: Obsevatories in Svetloe and Zelenchukskaya of VLBI Network QUASAR. In: Fourth APSGP Workshop, Eds. H. Cheng, Q. Zhihan, 47­57. Finkelstein, A. M., A. V. Ipatov, S. G. Smolentsev, V. G. Grachev, I. A. Rahimov, Z. M. Malkin, 2003: Highly Accurate Determination of the Coordinates and the Earth's Rotation Parameters Involving the Svetloe VLBI Observatory. Astronomy Letters, 2003, 29, No 10, 667­673. Himwich, E., 2000: Introduction to the Field System for Non-Users. In: IVS 2000 General Meeting Proceedings, Eds. N. Vandenberg, K. Baver, 86­90. Ipatov, A. V., I. A. Ipatova, V. V. Mardyshkin, 1994: In: Progress and Future Observational Possibilities, Eds. T. Sasao, S. Manabe, O. Kameya, M. Iniue, 200. Malkin, Z., A. Voinov, E. Skurikhina, 2000: Software for Geodynamical Researches Used in the LSGER IAA. In: ASP Conf. Ser., 216, Astronomical Data Analysis Software and Systems IX, Eds. N. Manset, C. Veillet, D. Crabtree, 632­635. Nothnagel, A., 2003: VTRF2003: A Conventional VLBI Terrestrial Reference Frame. In: Proc. 16th Working Meeting on European VLBI for Geodesy and Astrometry, Leipzig, Germany, 9­10 May 2003, 195­206. Smolentsev, S., D. Ivanov, Z. Malkin, 2001: Svetloe Radio Astronomical Observatory. In: 2000 IVS Annual Report, Eds. N. R. Vandenberg, K. D. Baver, 123­126.

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