The velocities of the Global Positioning System (GPS) stations are widely employed for numerous geodynamical studies. The aim of this paper is to investigate the reliability of station velocities and to draw reader’s attention that for proper estimates of velocity, we need to consider the optimal character of noise. We focus on a set of 115 European GPS stations which contributed to the newest release of the International Terrestrial Reference Frame (ITRF), i.e. ITRF2014. Based on stacked Power Spectral Densities (PSDs), we show that amplitudes o f seasonal signals are significant for nine harmonics of tropical year (365.25 days) and two harmonics of draconitic year (351.60 days). The amplitudes of tropical annual signal fall between 0.1-8.4 mm and are much higher for vertical component than for horizontal. Draconitic annual signal reaches the maximum amplitudes of 1.2 and 0.9 mm for North and East, respectively, whereas is slightly higher for the Up component with a maximum of 3.1 mm. We performed a noise analysis with Maximum Like lihood Estimation (MLE) and found that stations in Central and Northern Europe are characterized by spectral index between flicker and random-walk noise, while stations in Southern and Western Europe: between white and flicker noise. Both amplitudes and spectral indices of power-law noise show a spatial correlation for Up component. We compared the uncertainties of velocities derived in this study with a combination of power-law and white noises to the ones offici ally released in the ITRF2014 with a pure white noise. A ratio of the two estimates is larger than 10 for 13 % and 30 % of stations in horizontal and vertical direction, respectively with medians of 6 and 7. The large differences support the fact that at the velocity determination the proper noise characteristic should be taken into account to avoid any mislead interpretation., Anna Klos and Janusz Bogusz., and Obsahuje bibliografické odkazy
The paper presents the results of research related to the application of GNSS solutions in short observational periods in geodynamical investigations. Authors used the 3-hour solution appointed from hour-long interval of about 30 chosen stations on mountainous terrains from over 100 which were worked out. The main aim was to check the correctness of such solutions by the comparison with the daily ones. Some outliers in East component could testify, that tropospheric or ionospheric models used in the data adjustment are not sufficient for so short-time solutions. The second principal problem, which was considered in the present work is the ability to detect diurnal and sub-diurnal oscillations in changes of permanent stations’ coordinates. Results show unambiguously, that such oscillations appear in all analysed stations. In the paper there are examples of stations with dominant oscillations in different frequencies. The clear homogeneous in the frequencies was not found among any group of stations. It is therefore difficult to affirm, if their origin comes purely from the geodynamical phenomena., Andrzej Araszkiewicz, Janusz Bogusz, Mariusz Figurski and Karolina Szafranek., and Obsahuje bibliografii
We estimated the common seasonal signal (annual oscillation) included in the Global Positioning System (GPS) vertical position time series by using Multichannel Singular Spectrum Analysis (MSSA). We employed time series from 24 International GNSS Service (IGS) stations located in Europe which contributed to the newest ITRF 2014 (International Terrestrial Reference Frame). The MSSA method has an advantage over the traditional modelling of seasonal signals by the Least-Squares Estimation (LSE) and Singular Spectrum Analysis (SSA) approaches because it can extract time-varying and common seasonal oscillations for stations located in the considered area. Having estimated the annual curve with LSE, we may make a misfit of 3 mm when a peak-to-peak variations of seasonal si gnals are to be estimated due to the time-variability of seasonal signal. A variance of data modelled as annual signal with SSA and MSSA differs of 3 % at average what proves that the MSSA-curves contain only time-varying and common seasonal signal and leave the station-specific part, local phenomena and power-law noise intact. In contrast to MSSA, these effects are modelled by SSA. The differences in spectral indices of power-law noise between MSSA and LSE esti mated with Maximum Likelihood Estimation (MLE) are closer to zero than the ones between SSA and LSE, which means that MSSA curves do not contain site-specific noise as much as the SSA curves do., Marta Gruszczynska, Anna Klos, Severine Rosat and Janusz Bogusz., and Obsahuje bibliografické odkazy
This paper describes the researches upon the precise short-time GPS solutions made in the Centre of Applied Geomatics, Military University of Technology. The data from ASG-EUPOS (Polish Active Geodetic Network) was processed using Bernese 5.0 software and EPN (EUREF Permanent Network) standards and models. In this study, the adopted 3-hour observation window is shifted every hour obtaining geocentric coordinates in ITRF2005 reference frame. The adjusted network consisted of over 130 stations from Poland and the neighbouring countries, the period covered observations collected from 8.06.2008 to 18.06.2010. These two years of observations allowed to examine short-period oscillations which we found as closely related to the tidal (dynamic) frequencies. The analysis of the residua from IERS2003 tidal model was performed using least squares method with the Eterna software upon the idea of Chojnicki. It confirmed existence of the significant energy in the frequencies corresponding to S1, K1 and K2. The effects in S1 frequency reflect thermal influences, but the reasons of K1 and K2 existence could be both: dynamic (liquid core resonance and non-linearity of K1 are very difficult for modelling as well as the annual modulation of S1) or artificial (GPS satellites’ orbiting period, dynamic changes of satellites’ constellation and network geometry, multipath, residual tropospheric and ionospheric errors etc.). Since the phase of K1 for all 130 sites is very inconsistent the local effects could be also taken into account as one of the possible reasons. The paper describes the idea of the data processing and analysis, presents the results of vertical (Up component) oscillations in main tidal frequency bands, but also includes the discussion on the possible explanation of existence of short period oscillations in GPS precise solutions., Janusz Bogusz and Jan Hefty., and Obsahuje bibliografii
This paper contains the studies of the noise level in GPS (Global Positioning System) time series. As the data for this research the authors used changes of the geodetic coordinates of the ASG-EUPOS and associated (Slovak and Czech) sites. The method of precise GPS observations processing in short-time intervals was worked out in the Centre of Applied Geomatics, Military University of Technology. The authors focus on the diurnal and sub-diurnal frequency bands (tidal) as the tidal effects influence the sites’ positions at the most and the model used in the standard processing software does not contain geodetic coefficients. Thus the residual values of the geodetic coordinates time series should hold some information in the shape of coloured noise. The paper comprise short description of the Earth tides phenomenon, the concept of the tidal parameters determination, character of the white and coloured noise and the assessment of the noise estimation from GPS data. As the processed network contains 130 sites the spatial distribution of the noise’s parameters is also investigated., Janusz Bogusz and Bernard Kontny., and Obsahuje bibliografii
a1_The aim of this paper is to present the strategy of determination of the reference solution for the ASG-EUPOS (Active Geodetic Network - European Position Determination System) coordinate monitoring system. ASG-EUPOS is a network of permanent GNSS (Global Navigation Satellite System) stations controlled by the Polish Head Office of Geodesy and Cartography (HOGC), which main role is to realize the ETRS89 (European Terrestrial Reference System) in the territory of Poland. The Centre of Applied Geomatics (CAG) of the Military University of Technology (MUT) performs a control processing of the network and it is the leader of the ASG+ (the supporting modules for ASG-EUPOS system real-time services) project within which the coordinate monitoring system was developed. The coordinate monitoring is aimed to assess the actual performance of the GNSS stations and the reliability of the system and its services. The Polish realization of the ETRS89 is also controlled, where the deviation of the actual coordinates from the reference values are monitored. Furthermore, the monitoring enables the analysis of factors that degrade the individual GNSS stations and assess the solution stability which has impact on the quality of the determined geodynamic parameters. The reference solutions (coordinates and their changes over time) were determined according to the recommendations of the IAG sub-commission for the European Reference Frame concerning densification of EUREF. The paper presents the determination of the reference cumulative solution and the results of the processing of a few years long series of GNSS observations. The analysis are performed by the Bernese 5.0 and CATREF software. The results consists of daily and subdaily ASG-EUPOS reference solutions. They are also considered as input data for geodynamic studies to determine the horizontal and vertical velocity fields., a2_Estimation of the individual station velocities is of crucial importance for the ETRF (European Terrestrial Reference Frame) reference frame maintenance to assess the compatibility of the current station position with its catalogue (reference) value and apply coordinate correction if necessary., Karolina Szafranek, Janusz Bogusz and Mariusz Figurski., and Obsahuje bibliografii
Presently the determination of the velocity field in the global reference frame is possible by using different space techniques and dense terrestrial networks from global to local and regional scales. However, the reliability of such determinations is strongly limited by the restricted number of unmodeled effects. Some of them are periodic (atmospheric or hydrological effects), some instantaneous (natural or man-made seismicity ) or seasons-related (snow cover, freezing). This elaboration deals with the unmodeled effects observed in the ASG-EUPOS (Polish Active Geodetic Network) time series. The whole network consists of over 130 permanent GNSS sites with different levels of stability. The paper presents the analysis of 3-year’s time-series of geodetic coordinates (in the topocentric projection) in order to obtain best-possible local velocity field. On the example of the Sudeten region, where 19 sites are located, the possible effects on the decrease in reliability of the velocity field determination are described. Finally the local velocity field in ITRF and ETRF frames are presented., Janusz Bogusz, Mariusz Figurski, Bernard Kontny and Piotr Grzempowski., and Obsahuje bibliografické odkazy
The results presented in this paper concern investigation of environmental influences to GNNS coordinates on the example of ASG-EUPOS network. The problem of the impact of environmental effects is crucial for observing gravity. Satellite systems are not as susceptible to changes in local hydrology or atmospheric effects, although significant influences are clearly visible in the change of coordinates. The authors analyzed daily and sub-daily solutions (geocentric coordinates) in the context of different disturbances to eliminate sites suffering from poor quality for further researches (e.g. data from the most reliable ASG-EUPOS stations will be used for investigating the correlation of their movements with the lithosphere deformations on territory of Poland). There are many doubts regarding proper antennas’ placement - as they are mostly placed on the roofs, there were questions if data from these sites can be used for scientific purposes like velocity estimations or geodynamical researches. Analysis of daily solutions was supposed to prove that the majority of Polish sites give fully valuable data. Some factors that may cause a precision decreasing can be avoided or eliminated in the future. Taking into consideration that GLONASS will be soon fully operational and it will be an alternative for commonly used GPS, the authors made separate elaboration of GPS and GLONASS data. Usage of two different satellite systems holds the potential to increase of solutions’ reliability and eliminate errors that could be possibly related to the specific satellite system. Base on time series of coordinates residual values, systematic errors that could prove geophysical and geodynamical influence on GNSS measurements were investigated. In this elaboration only post-processing observations were taken into account, but the monitoring of the network in the near real-time by means of coordinates’ stability is under development., Janusz Bogusz, Mariusz Figurski, Krzysztof Kroszczyński and Karolina Szafranek., and Obsahuje bibliografii
The GRID_STRAIN software that runs under the MATLAB® environment helped us in achieving the continuous strain field model. Unfortunately, the program averages the results. Therefore, the authors’ main goal of this paper was to work out a method of good verification of data to avoid falsifying of the results of strain calculations. We decided to use the method of the Delaunay triangulation to build a set of triangles of the data (EPN and ASG-EUPOS stations as the vertexes) and by the use of the velocities of each point and their errors, to estimate the single strain in each triangle. This approach made it possible to exclude the outlying values from the data. Selection of the criteria of the characteristic of insufficiently stable points in order to remove them from further computations is of a great importance for the final results of computations of the deformation field. In such a tectonically stable region, as the area of Poland, the strain values should not be higher than 3 to 4 nanostrains/year. At the low rate of tectonic deformations observed in Poland, the disturbances resulting from insufficient stabilization of the ASG-EUPOS network influence the computations of the deformation field to a significant extent. Improper stabilization of a single permanent station causes unification of the deformation field within 2 to 3 computation triangles having a common vertex at this station. Based on this assumption, nearly 30 of the ASG-EUPOS stations were excluded from further strain calculations. The analysis of the geodynamic consistency of the deformation field for the computation triangles is basis for indicating stations for which the dislocation resulting from insufficient stabilization, significantly exceeds the dislocation resulting from the deformation of the lithosphere. Most of the ASG-EUPOS network stations may be used for analysis of local differentiation of the deformation field in Poland., The regularities of the deformations distribution determined by ASG-EUPOS network stations constitute a new set of data which will be used for further geodynamic interpretation. In case of lower rank disturbances resulting from destabilization of the network stations, this factor’s component cannot be recognized using qualitative analysis of the deformation field., Janusz Bogusz, Anna Klos, Mariusz Figurski, Marek Jarosinski and Bernard Kontny., and Obsahuje bibliografii
The paper concerns analysis of solutions obtained during common processing of data from GNSS permanent stations situated on mountainous terrain: the Western Carpathians, the Sudetes Mountains and adjacent areas. As the outcome daily and weekly solutions (ellipsoidal coordinates) of forty Polish, Czech, Slovak, Ukrainian and German sites were obtained. Weekly solutions were used to determine velocity field and vertical movements, daily solutions enabled quality and precision of sites’ coordinates estimation to check if permanent GNSS sites can be used as a stable reference frame for geodetic, geological and geodynamical measurements in the mountainous area. First investigations concerning data from permanent GNSS stations in the Sudetes Mountains were made in 2007 using daily solutions from EPN sites obtained in test reprocessing of the whole regional network performed in Centre of Applied Geomatics. Since that time, national systems became operational increasing density of GNSS network, so the data can be used for wider range of investigations. As the majority of examined stations started to gather data in 2008, analysis were based on relatively short observation period, so they rather play a role of tests for further investigations and they give the preliminary estimation of individual sites’ activity., Mariusz Figurski, Karolina Szafranek, Janusz Bogusz and Paweł Kamiński., and Obsahuje bibliografii