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Polska sieć geodynamiczna, 1997 - epoka 0

Dobrzycka M., Cisak J.

Prace Instytutu Geodezji i Kartografii

2001

T. 48, z. 103

61--81

W artykule opisano prace nad założeniem, pomiarem i wynikami opracowania obserwacji GPS w Polskiej Sieci Geodynamicznej (PSG). Otrzymane współrzędne punktów tej sieci porównano z wynikami wcześniejszych kampanii EUREF-POL i POLREF służącymi do utworzenia katalogu współrzędnych punktów podstawowej osnowy geodezyjnej kraju. Stwierdzono przy tym różnice o wyraźnie systematycznym charakterze. Omawiając możliwe źródła ujawnionych rozbieżności, zwrócono szczególną uwagę na efekt modelowania wysokości centrów fazowych anten, organizując specjalną, dwudobową kampanię testową na Krajowej Bazie Długościowej Warszawa-Bemowo.

Reflecting natural and man-induced tectonics the position of the network points do change in time. Their motion can be monitored by repetitive measurements using modern geodetic methods. According to current trends and international recommendations the so called geodynamic network was established in Poland, aiming at monitoring coherency and stability of the primary control network, contributing to regional and global geodynamic investigations and providing unified frame for local geodynamic programs. The geodynamic network was set up in the first half of 90-ties. It consists of 36 points. Most of them (33) were chosen from nearly 400 – points of primary network that was in the process of fundamental modernisation. Location of points (Fig.1), consulted with geologists, gives coverage to main and subordinate crustal blocks. Monumentation of points (not fully uniform) is shown in Fig.2. The geodynamic network includes five permanent GPS stations of the “GPS Permanent EUREF Network” and seven remaining 0-order EUREF points, serving as an extension of ETRS system. 0-epoch GPS campaign in the Polish Geodynamic Network (PSG) was carried out in September 1997, in five three-day sessions, using eight sets of Leica receivers. The observations were processed and adjusted in co-operation with WUT Analysis Centre of the „GPS Permanent EUREF Network” program, using Bernese 4.0 software, according to presently valid standards. As the reference points served all five Polish GPS permanent stations, as well as five stations in neighbouring countries. Vectors used in adjustment are shown in Fig. 4. The results of 0 - epoch campaign were compared to those from former campaigns: EUREF-POL (1992) and POLREF (1994–1995). The differences obtained in latitude, longitude and ellipsoidal height are shown in Table 1 and illustrated in Fig. 5, in order to better indicate their systematic character that is especially significant in the height component. Looking for reasons of such results several possible sources were considered, among them steadily changing, different ITRF frame parameters, used for elaboration of different campaigns (91 for EUREF-POL, 94 for POLREF and 96 for PSG), as well as different versions of computing program, methods of adjustment and ties selections. Special attention however, was paid to the antenna phase centre effect. In both POLREF (1994–1995) and PSG (1997) campaigns 8 Leica SR299 and SR399 receivers were used. At the reference points different sets of instruments were operating and different antenna characteristics were used: old and new, provided by manufacturers and recommended by IGS, model IGS 01/1996. Differences between old and new characteristics of the selected antenna types are shown in Table 2. To test the validity of the antenna heights used in PSG measurements, two day's long GPS campaign on the Polish Standard Baseline Warszawa-Bemowo was conducted (see Fig.6), with use of the majority of GPS antenna applied in the PSG campaign. On the first day instruments were installed in direct while on the next day in the reverse order. Differences in calculated height and distance between each pair of antennas in both setting orders, were compared with standard values (accuracy better than 2mm, obtained from multiple precise EDM measurements and geometric levelling). The results shown in Table 3 may suggest erroneous value of height component for Leica and - smaller – for DM model T antenna phase centre, while four other antenna types show very good agreement. Authors present one more possible source of discrepancies between results of different campaigns, reflected in rather regular, periodic variations of point positions. Not yet modelled, they are well documented by observations at permanent GPS stations (see Fig. 7) and possibly caused by not enough sufficient modelling of tidal effects. The reliable interpretation of results from different GPS campaigns is not easy, it needs very detailed information about instruments, methods and options of program used. Sometimes, when considering sophisticated tasks, re-computation might be appropriate.

Obserwatorium astronomiczno-geodezyjne w Borowej Górze

Moskwiński M., Dobrzycka M

Prace Instytutu Geodezji i Kartografii

1998

T. 45, z. 96

7--18

W artykule podany jest rys historyczny, okoliczności powstania Obserwatorium, losy wojenne i etapy rozwoju do chwili obecnej.

Astronomical Observatory in Borowa Góra was established after First World War, when task o f setting basic framework for the whole country at uniform coordinate system was assigned to the Polish Geodetical Service. According to the parliament act o f April 25, 1925 the Ministry o f Public Works was responsible for all works related to this task execution. Borowa Góra station, located at central part o f Poland, was selected as the main point o f astronomical -geodetical network. At the same time, being the tangent point o f geoid and reference ellipsoid, the station served as the origin o f „Borowa Gora” coordinate system. This was obligatoiy in geodetical works until „1942” and „1965” coordinate systems were implemented. First measurements at „Borowa Gora” point, aiming at determination o f its geographic coordinates, were started in 1929. The works conducted at the gradually developing Observatory were interrupted at the beginning o f the WorldWarin 1939. Instruments and all equipment o f the laboratory were robed by German occupation authorities, while the building was occupied by German military post. The observatory building and autdoor constructions were almost completely destroyed during passing front in 1944. After the war the Observatory was rebuilt and developed; it served, as previously, for executing works related to setting and unification o f triangulation network within the changed boundaries o f Poland. In 1963, after several years' preparations, examination o f irregularity o f the Earth rotation was started. Observatory joined international geodynamic programs developed successively following the progress in measuring techniques, especially through the application o f satellite methods. Photographic camera satellite observations were conducted from 1972 to 1977; continuous observations using Doppler receiver were carried out from 1984 to 1990 and, since 1996 GPS Ashtech ZXII3 receiver is in use. At the same time Borowa Gora Observatory was incorporated into the network of the permanent European stations (GPS Permanent EUREF Network program) and in 1997 it joined the EUVN program (European Vertical Reference Network). The Observatory in Borowa Gora also takes part in the other global, regional and local programs and campaings.