The main objective of CERGOP-2/Environment Work Package was defined in the Project as "Monitoring the CEGRN by regular and systematic GPS measurement, satisfying the strict quality standards set by WP2". The main task in the course of the Project was the organization of the CEGRN epoch observation campaigns. Therefore the activies focused on the preparation and the careful realization of these measurements. Two CEGRN campaigns were carried out- CEGRN03 and CEGRN05 - in the same part of the year (in June) in order to minimize seasonal effects in the measurements. In both cases the CEGRN campaigns were overlanned with national campaigns (e.g. in Hungary the HGRN epoch campaigns) by which the scope and efficiency of data availability were greatly enhanced. An other task was to monitor the status of CEGRN. Due to the project support 25 new sites became part of CEGRN, Serbia as a new CEGRN Consortium member (not included in the Project) joined the campaigns in 2005 the first time.
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The main objective of CERGOP Work Package (WP-3) is defined in the project as "Monitoring the CEGRN by regular and systematic GPS measurement, satisfying the strict quality standards set by WP 2". This reporting period was "between campaigns" and therefore the main activities focused on maintenance and extension/densification of the existing CEGRN. The preparation of the CEGRN`05 epoch campaign is the task of the Hungarian group. We have distributed the circulars for the compaign call in early 2005. The CEGRN`2005 will be carried out in 20-25 June 2005 overlapping with the HGRN`05 epoch campaign. Several other activities were carried out in relation to the project e.g. footprint monitoring and the search for a new permamnent site in Hungary.
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The main objective of CERGOP Work Package (WP)-3 is defined in the project as "Monitoring the CEGRN by regular and systematic GPS measurement, satisfying the strict quality standards set by WP 2". The milestone of the first year was the first epoch GPS observational campaign with full participation of all the contractors.
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Civil users of the NAVSTAR Global Positioning System (GPS) in Hungary are experiencing occasinal severe interference at the GPS signal frequency of 1575,42 MHz. As the application of the GPS technique spread rapidly in our country , radio frequency interference (RFI) should be considered a serious threat to widespread applications. The new geodetic control network (OGPSH) in Hungary is based on GPS measurements by which more than 1100 sites have been established. The paper reports the experiences gained during this work. Interference sources could be tracked to ground based telecom digital data transmissions which are operating mostly in Western part of Hungary. telecomminication regulations exceptionally allow such transmissions in specified countries. In order to warn potential GPS users mapping of the interference sources are being carried out.
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Hungary joined to EUREF in 1991. In the same time a multipurpose 24-point GPS frame network was also established in the country. Because of the disagreement on the further development of the Hungarian GPS network, the densification was very much delayed and the site selection was started only in 1994. The Hungarian National GPS Network (OGPSH) is primarily designed for surveying applications. It is exclusively based on points of the existing horizontal control network (EOVA), where reliable GPS measurements could be performed easily. New sites were monumented only where suitable existing site was not found. The mean distance between the points is about 10 km. This relatively dense distribution was chosen, because of its more efficient field measurement technique. The selected more than 1150 points had been measured in three campaigns between 1995 and 1997 covering altogether 41 working days. In the campaigns 9 observer groups were participated and measured 4-6 sessions per day. The GPS data were processed each day in the field using Trimble's GPSurvey software. The network adjustment was done with our software, developed for large GPS network adjustment. The adjustment had shown good results, the horizontal position accuracy was at the one-cm level. The GPS coordinates refer to ETRS89, epoch 1989.0. In the OGPSH network only 340 sites have leveled height. Based on the technique developed at our Observatory, all sites were supplied with sea-level height using the GPS-gravimetric geoid. The height component accuracy is estimated about 3-5 cm. A new , GIS-based database was developed as well, which contains all relevant information (site descriptions, coordinates). This digital database is being used at the Land Registry Offices for serving the surveyors.
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