Abstract
The paper analyzes the geodynamic network of the City of Zagreb for periodic campaigns carried out from 2006 to 2009 which were processed by different software packages. The first computations and processing results were obtained by using the scientific software Gamit/Globk and indicate the ongoing tectonic activity of the area. In this paper, all calculations were performed by using the scientific software Bernese. Processing strategies and applied error models in the Gamit and Bernese solution are analyzed. The results of the previous analyses show the need to perform GNSS measurements at intervals of up to one year, which is necessary for understanding the mechanism of the structural frame of the wider Zagreb area. The research and analysis performed in this paper indicate certain uncertainties in determining the velocities from periodic one-year GNSS measurements. When periodic GNSS observations are analyzed at time intervals shorter than 2.5 years, annual signals can cause significant errors in determining point velocities. The accuracy of determining velocities between annual time intervals depends on a number of factors: noise level in GNSS measurements, measurement sessions quantity and applied computation strategies. Previously, the time series analysis of observations was a key procedure in the context of geodynamic and geokinematic research and the FODITS algorithm was used for the analysis. A noise analysis on the daily time series of coordinates was performed for the purpose of understanding all influences on geodynamic points. Moreover, a correlation between the time series of observations was determined in order to estimate the final velocity uncertainty error. The purpose of this paper is to demonstrate the applicability of the methods and procedures used to determine the coordinates and velocities of points that can be reliably used for geodynamic and geokinematic analyses and consequently, timely responses to various geophysical phenomena due to earthquakes or other natural phenomena.
Highlights
Previous calculations for establishing the reference frame and investigating geodynamics have made it possible to determine the character and parameters of the displacement of the Earth's crust in the territory of the Republic of Croatia [1,2,3,4,5]
Using the GNSS observation data from the geodynamic network of the City of Zagreb for the period from 2006 to 2009, different error models and GNSS measurement processing strategies were analyzed with the possibility of eliminating systematic and random influences
It can be seen that for linear velocities in the 2.5 periods, these differences are below mm, which directly indicates the connection between a higher measurement noise and the processing strategies implemented in software solutions
Summary
Previous calculations for establishing the reference frame and investigating geodynamics have made it possible to determine the character and parameters of the displacement of the Earth's crust in the territory of the Republic of Croatia [1,2,3,4,5]. The investigations carried out in this paper relate to examining the impact of the chosen error modeling method and the GNSS measurement processing strategy, while analyzing the time series of observations and the influence of time intervals between the observations on the accuracy and the precision of the points’ coordinates and velocities. Based on the collected observations of the Geodynamic Network of the City of Zagreb (GNCZ), the application of various error modeling methods and processing strategies for GNSS measurements has been analyzed, with the possibility of eliminating their systematic or random influences, which will enable their reliable use for geodynamic and geokinematic analyses. Seismic deformation modeling helps detect discontinuities in the time series of GNSS coordinates, which is one of the main sources of error in determining the ITRF frame today [8]. The magnitudes for white and pink noise are expressed in mm and for red noise in mm/yr
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