Proceedings of Research Works 1998 250 66 Zdiby 98, tel. 02/685 7375, fax: 02/685 7056, e-mail: odis@vugtk.anet.cz

1. Introduction

2. Geodetic and Geodynamical Projects of the Central European Initiative

The activities within the CEI/C are divided into three subprojects: C1 - "Interconnection of Geodetic Networks", C2 - "GIS/LIS" and C3 - "Geodynamics". The most important international projects currently run in the subproject C3 are CERGOP (Central Europe Regional Geodynamics Project) and UNIGRACE (Unification of Gravity Systems of Central and East European Countries). All activities of the section CEI/C are by the decision of the CEI Earth Science Committee Round Table Session, held in Trieste in December 1994, concentrated in one main project "Geodynamics and Geo- environmental Problems in the Circum Pannonian and Adjacent Regions" (GEOPAR). This complex project comprises also several partial projects of the CEI sections A "Geology" and B AGeophysics@. Such an approach leads to a strong enhancement of the interdisciplinary character of geodetic investigations. The following more detailed description of the projects CERGOP and UNIGRACE gives some insight into the essence of the present international cooperation among Central European countries in geodesy and geodynamics.

2.1 Central Europe Regional Geodynamics Project (CERGOP)

To support the geoscientific research of the region by highly accurate, reliable and homogeneous geodetic measurements, a joint project called Central Europe Regional Geodynamics Project (CERGOP) was launched in 1994. This complex project, which is aimed at investigations of geodynamical effects by geodetic methods, was initiated in 1993 by Hungarian and Polish geodesists, see (Fejes, 1993). The project is being jointly realized by the institutions of Austria, Croatia, the Czech Republic, Germany, Hungary, Italy, Romania, Poland, Slovakia, Slovenia and Ukraine. Bulgaria joined the project in 1996 as an associated country. The project is coordinated by the International Project Working Group (IPWG) which is responsible for the progress and scientific level of the project. Each of eleven participating countries is in the IPWG represented by one delegate.

In the first step the geodetic investigations should mainly be based on GPS technique and to this goal the international Central European GPS Reference Network (CEGRN) was established in 1993 - 94. This network represents the main tool to achieve the project objectives. It consists of 31 stations located on representative geological structures and monumented according to the international standards. The distribution of the CEGRN stations is shown in Figure 1. For the Czech Republic the IGS/EUREF station GOPE (Geodetic Observatory Pecný) and the station Polom (Military Topographic Institute Dobruška) in Orlické hory, which is also the station of the Czech Fundamental Geodynamical Network, were included into CEGRN. Nowadays 11 permanent GPS stations are being operated within CEGRN including some collocation stations (SLR, VLBI).

In the period 1994 - 1997 four CEGRN monitoring GPS campaigns were carried out in about the same time of the year (May, June) to avoid possible seasonal effects. The observational data were transfered via Internet to the CERGOP Data Center in Graz, Austria where they are made available for processing. The processing has been made independently by eight processing centers (Graz-Austria, Penc-Hungary, Warsaw-Poland, Pecný-Czech Republic, Bratislava-Slovakia, Leipzig-Germany, Matera-Italy, Zagreb-Croatia). Most of the processing centers, including the Czech one, used the Bernese software package version 3.5 and later 4.0. The work of the centers was evaluated by the special study group No.4 AStandardization of Data and Processing Centers@ chaired by Graz group. In 1994 - 95 special CERGOP study groups (CSG) were formed to carry out more detailed research in a particular field. Originally 11 CSGs were setup and 9 of them have remained active to the present time:

• CSG 2 CERGOP Site Quality Monitoring (P.Lévai, Hungary)
• CSG 3 CERGOP Reference Frame (J. Rogowski, Poland)
• CSG 4 Standardization of Data and Processing Centers (G. Stangl, Austria)
• CSG 5 Permanent and Epoch GPS CERGOP Stations (J. ledzi ski, Poland)
• CSG 6 CEGRN and Height Determination (J. Šimek, Czech Republic)
• CSG 7 CERGOP Gravity Network (M. Barlik, Poland)
• CSG 8 Geotectonic Analysis of the Region of Central Europe (P. Vysko il, Czech Republic)
• CSG 10 Monitoring of Recent Crustal Movements in the Eastern Alps (C. Marchesini, Italy)
• CSG 11 3-D Plate Kinematics in Romania (D. Ghitau, Romania).

The progress in the project CERGOP has been periodically evaluated twice a year at working conferences and all results achieved in observation campaigns or in the work of study groups have been regularly published in the international series Reports on Geodesy edited by the Institute of Geodesy and Geodetic Astronomy, Warsaw University of Technology. Among the results of the work of CSGs one of the most remarkable results is the publication of five monographs devoted to the problems of geodynamics of different parts of Central Europe. This monograph series was compiled by the members of the CSG 8 AGeotectonic Analysis of the Region of Central Europe@ (chairman P. Vysko il, VUGTK). All five volumes were edited and printed by the IGGA WUT Warsaw in the international series Reports on Geodesy. The individual volumes are devoted to the Panonian Basin (editor G. Grenerczy), Bohemian Massif (P. Vysko il), Teisseyre-Tornquist Zone (J. Liszkowski), Northern Carpathians (F. Zablotsky) and Southern Carpathians (D. Ioane). The monographs summarize the latest geoscientific results on corresponding regions with a particular emphasis on the CERGOP objectives.

The CEGRN with its 11 permanent stations represents a Central European Terrestrial Reference Frame (CETRF) which can serve as a basis of the hierarchical structure of the deformation monitoring networks for more detailed investigations on territories of individual participating countries. In the Czech Republic this structure is formed by the Czech Fundamental Geodynamical Network (32 stations) and three local monitoring networks setup in areas with increased geotectonic activities, see Fig. 2.

A more comprehensive information about objectives and achievements of the CERGOP project as well as about future plans for its continuation can be found in (Fejes et al., 1998).

2.2 Project UNIGRACE - Unification of Gravity Systems of Central and Eastern European Countries

The merit of the project UNIGRACE consists of repeated absolute gravity measurement at 17 sites in 12 countries (Austria, Bulgaria, Czech Republic, Croatia, Finland, Hungary, Germany, Italy, Poland, Romania, Slovakia and Slovenia). Among these 12 sites there are intraplate and tide gauge sites. The intraplate sites have been selected with respect to their geological stability. They will provide a unique gravity system and gravity scale in accordance with the SI system of units. The tide gauge sites have been added to the network in order to contribute to the unification of the height systems of the participating countries as well as to the sea level variation studies. Most of the sites are also included in international GPS networks like CEGRN and EUVN. The stations have been selected and established with respect to the international standards.

The absolute gravity meters necessary for the realization of the project will be provided by Austria, Finland, Germany, Italy and Poland. Two observation campaigns at each site are scheduled for 1998 and 1999-2000. At the beginning and at the end of the campaign a common calibration of the instruments employed in the campaigns will be carried out at one station (Wettzell, Germany and Józefoslaw, Poland). In addition to it, all five absolute gravimeters were checked and intercompared during the international campaign at BIPM, Sévres in fall 1997. The repeated campaigns will be performed by different absolute gravimeters.

The absolute sites will be connected by high precision relative gravity measurements to national gravity networks. To be able to reduce the observed absolute gravity to a conventional level the vertical gradients at the absolute sites have to be determined with a maximal attainable accuracy.

From the Czech Republic the absolute gravity station at the Geodetic Observatory Pecný has been chosen for the project UNIGRACE. From October 1978 to October 1997 nine absolute measurements were carried out at this station by five different agencies and five absolute meters. The results were corrected in the same way for the influence of the air pressure, polar motion and of the earth and ocean tides. The results are summarized in (Šimon, 1997). It is expected that the absolute measurements which will be carried out within the project UNIGRACE will contribute to setting up a national gravity standard represented by this station. The following benefits of the project are basically foreseen, see (Reinhart et al., 1997):

• to determine the absolute gravity standard in SI units with the highest possible accuracy,
• to transfer the gravity standard for the precise determination of weights and related instrumentation like high precision scales and pressure sensors,
• to improve the testing methods and the compatibility of laboratories between the EU countries and the other European countries,
• to provide the gravity standard as a necessary prerequisite for a common definition of a unique European height system,
• to establish calibration lines for relative gravimeters,
• to establish a common gravity standard for an exact intercomparison of sea levels of the Adriatic, Black and Baltic Sea,
• to improve and stabilize the research and development technology potential in the Central and Eastern European countries.

3. Activities Towards Maintenance and Unification of the European Reference Frame

• to establish a geodetic reference system for any precise geodetic or geodynamical project on the European plate,
• this system should be very close to the WGS-84 to be used for geodesy and for all sorts of navigation in Europe,
• to represent a continent-wide modern reference for multi-national Digital Cartographic Datasets.

The maintenance and densification of the ETRF89 was mainly done using GPS campaigns where sites with known ITRF coordinates were fixed during the processing. These sites were in the first place the European SLR/VLBI sites and later also IGS (International GPS Service for Geodynamics) sites. After a three-month test campaign (June - September 1992) followed by a pilot service, the IGS had been formally established by the IAG in 1993 and started its routine work on January 1st, 1994. The primary objective of the IGS is to provide a service to support geodetic and geophysical research activities by GPS data products. With regard to the growth in GPS applications the secondary objective of the IGS is to support a broad spectrum of operational activities performed by governmental and some commercial organizations. The IGS accomplishes its work through the following components: networks of tracking stations, data centers, analysis and tracking using high accuracy receivers and data transmission facilities allowing for a rapid data transmission to the data centers. The global distribution of IGS stations is shown in Figure 3. Since September 1995 the Geodetic Observatory Pecný has been an IGS operational station.

3.1 Geodetic Observatory Pecný - IGS Operational Station GOPE

A permanent GPS station has been in operation since September 1993 and since September 1995 it has been regularly contributing to the IGS. The antenna is mounted in a metal plate with a forced centering embedded on the top of a concrete pier over the roof of the main observatory building. The pier passes througt the building and is embedded in its grounds. Around the upper part of the pier there is an observing platform containing the meteorological box with a sensor for recording meteorological data (temperature, air pressure, humidity). The daily observation data are downloaded at 0:05 UTC and RINEX daily files are routed via the Internet to the Data Center of the CEI in Graz and further forwarded to the IGS Regional Datacenter BKG Frankfurt am Main. At present the station operates fully automatically. In station reports weekly published by the IGS Central Bureau the prevailing evaluation of the station data transfer. In addition to permanent GPS observations also permanent gravimetric observations of the earth tides have been performed at GOPE tidal laboratory since 1970. Beside the on-site continuous data processing and analysis the results are supplied to the International Center on Earth Tides in Brussels, Belgium. Also the time and latitude astrometric observations have been regularly performed here since 1957. These data are supplied to the World Center of Optical Astrometry in Shanghai, China and to the GOSSTANDARD, Russia.

3.2 EUREF Local Analysis Center at the Geodetic Observatory Pecný

The EUREF-LAC at the station Pecný (GOPE) has been operated since January 1997 in cooperation between the VUGTK and the Department of Advanced Geodesy, Czech Technical University Prague. The data of 13 IGS/EUREF permanent stations are continuously processed by the Bernese GPS software version 4.0 which includes the Bernese Processing Engine. A special program superstructure has been developed for fully automated data processing, see e.g. (Douša, 1997), (Douša and Ehrnsperger, 1997), which is run in the Debian Linux 1.3 environment. Every night the main processing script, which coordinates all others, is started using unix cron daemon. The processing strategy meets the present standards adopted by the working group for EUREF LAC. The weekly solutions of the processed subnetwork are as weekly SINEX files available for a combined solution. The distribution of the stations processed by the EUREF-LAC GOP is displayed in Fig. 5 and the four principal parts of the model of routine permanent GPS data processing used in EUREF LAC GOP are schematically represented in Fig. 6. A list of permanent stations processed by EUREF LAC GOP is given in the following Table 1 along with more detailed information about the stations. The signs "+" and "-" indicate that the corresponding station was included or excluden from the cluster assigned to LAC GOP during 1997.

3.3 Analysis of the Results of Permanent GPS Observations

3.3.1 Evaluation of Long-Period Solutions of the EUREF-LAC GOP

4. Contribution of the Geodetic Observatory Pecný, VUGTK to EUVN

• a contribution to a unique European height datum,
• connection of the European tide gauge benchmarks for monitoring sea level variations,
• realization of fiducial points for the European geoid determination,
• preparation of a European Vertical Kinematic Network.

The EUVN consists of 195 sites distributed over entire Europe, see. Fig. 9. Of these sites 79 are EUREF stations, 53 nodel leveling points and 63 tide gauges. For each EUVN site 3-D coordinates in ETRF89 and the geopotential number referenced to UELN have to be determined. The EUVN GPS observation campaign was carried out in the period May 21 - May 29, 1997. The Czech Republic took part in this campaign by observations at four Czech EUVN stations (3 first order leveling bench marks and 1 EUREF station). Later also Czech IGS station GOPE was included into the EUVN network. The precise leveling link between the fundamental leveling benchmark Pecný and IGS/EUVN station GOPE (about 100 m) was made by the Land Survey Office.

The data preprocessing after the EUVN campaign was performed by 9 EUVN Preprocessing Centers (PPC). One of them was the PPC GO Pecný, Czech Republic. The aim of the preprocessing was to check the completeness and consistency of the data and of the auxiliary information. The EUVN Data Center is working at the BKG Leipzig. The PPC GOP made data preprocessing from the following EUVN national subnetworks: Czech Republic (4 + 1 sites), Denmark (5 + 1), Hungary (4), Slovakia (3), Slovenia (3). The preprocessing was made in accordance with the Technical Requirements and Guidelines for the EUVN Campaign elaborated by the EUVN Technical Working Group. The results are presented in (Karský and Šimek, 1997).

After the preprocessing of the entire EUVN network had been finished, 10 EUVN Analysis Centers started the processing of the EUVN network which was divided into 10 subnetworks. The EUVN Analysis Center Czech Republic (Geodetic Observatory Pecný) was responsible for the processing of the subnetworks of Spain and Portugal with overlappings to France and Mediterranean, see Fig.10. The subnetwork consists of 23 EUVN stations, six of them being IGS stations. According to the specifications approved by the EUVN TWG the computations of the Iberian subnetworkwere performed considering the following three strategies: solution with 15 deg. cut-off angle without weighting, solution with 15 deg. cut-off and satellite dependent weighting and the solution with 5 deg. cut-off and elevation dependent weighting. Accuracy investigations were based on the analysis of daily solutions, on the repeatability for each computational strategy as well as on the comparison of the unweighted 15 deg. and elevation dependent 5 deg. solutions. It can be concluded that the 5 deg. solution shows smaller rms errors of both the daily and the final solution of the network than the other solutions. No clear differences were detected in the repeatability and there are also no significant differences in the coordinates. The residuals of the 7 parameter Helmert transformations between different solutions are within 1 mm for N-S and E-W components and within 5 mm for the up- component (Lukeš, 1998). The accuracy estimates of the results obtained by the EUVN Analysis Center GOP are illustrated in Figs 11, 12, 13.

5. Other International Activities

Some problems related to a detailed investigation of the outer gravity field have been recently solved in broader cooperation of the Astronomical Institute, Academy of Sciences of the Czech Republic, VUGTK-GO Pecný, NOAA, Silver Springs, USA and the German Geodetic Research Institute Munich (DGFI). Among the results of this cooperation perhaps the most important are the contribution to the use of dual-satellite cross-over latitude lumped coefficients in geodesy and oceanography, see (Klokočník et al., 1996), determination of gravity field parameters from single and dual satellite cross- overs, see (Bosch et al., 1997) and the study of a possible impact of the Earth´s free oscillations on satellite orbits, see (Kostelecký et al., 1996). The cooperation between AI Asci CR, VUGTK and NASA GSFC (USA) was aimed at testing the geopotential model EGM96 (Klokočník et al., 1997).

In the International Association of Geodesy a representative of the VUGTK has a function of the President of the Section IV - "General Theory and Methodology", and is the member of the IAG Executive Committee. Also the membership of the scientists of the Institute in other IAG structures like the special commission for mathematical and physical foundations of geodesy, Committee for Education, SSG 3.164 (Instruments and Methods of Airborne Gravimetry), IAG International Commission for Earth Tides, Commission X - AGlobal and Regional Geodetic Networks@, SSG 3.166 "Modelling and Interpretation of the local Gravity Field" should be noted here. The activities within the IAG can be found on Internet in the homepage of the IAG Central Bureau http://www.gfy.kw.dk/iag/. The staff member of the VUGTK also works in the panel ASatellite Orbit Dynamics@ of the COSPAR, four are members of the European Geophysical Society, one of the American Geophysical Union and of The New York Academy of Sciences. One scientist of the VUGTK is a member of the editorial board of the international journal Journal of Geodesy.

In the Section C - Geodesy, Earth Science Committee of the Central European Initiative, one staff member of the VUGTK has a function of the national coordinator for the Czech Republic and of the international coordinator of the subproject C1 - Interconnection of Geodetic Networks. Two study groups of the international project CERGOP are chaired by the staff members of the VUGTK, see. paragraph 2.1.

6. Conclusions and Acknowledgments

7. References

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