Danijel Šugar

In this paper we analyze and visualize the arches of the athletic track on the high school playground near the Faculty of Geodesy in Zagreb based on surveying methods. A total of 129 numbered points were observed by the terrestrial method (tachymetry) and the final coordinates were obtained by subsequent data processing. We apply and compare three least squares methods of curve fitting on the data set to obtain equations of ellipses that are closest to observed points and visualize them using Grasshopper and Rhinoceros 3d. After finding the coefficients of ellipse equations, five ellipse geometrical parameters we estimate along with their error assessments.

Global navigation satellite systems (GNSSs) are an integral part of modern society and are used in various industries, providing users with positioning, navigation, and timing (PNT). However, their effectiveness is vulnerable to signal interference, since GNSSs are based on received satellite signals from space, and that can severely impact applications that rely on continuous and accurate data. Interference can pose significant risks to sectors dependent on GNSSs, including transportation, telecommunications, finance, geodesy, and others. For this reason, in parallel with the development of GNSSs, various interference protection techniques are being developed to enable users to receive GNSS signals without the risk of interference, which can cause various effects, such as reducing the accuracy of positioning, as well as completely blocking signal reception and making it impossible to obtain positioning. There are various sources and methods of interfering with GNSS signals, and the greatest consequences are caused by intentional interference, which includes jamming, spoofing, and meaconing. This study investigates the effects of jamming devices on static GNSS observations using high-accuracy devices through multiple controlled experiments using both single-frequency (SF) and multi-frequency (MF) jammers. The aim was to identify the distances within which signal interference devices disrupt GNSS signal reception and position accuracy. The research conducted herein was divided into several phases where zones within which the jammer completely blocked the reception of the GNSS signal were determined (blackout zones), as were zones within which it was possible to obtain the position (but the influence of the jammer was present) and the influence of the jammer from different directions/azimuths in relation to the GNSS receiver. Various statistical indicators of the jammer’s influence, such as DOP (dilution of precision), SNR (signal-to-noise-ratio), RMS (root mean square), and others, were obtained through research. The results of this study indicate that commercially available, low-cost jamming devices, when operated within manufacturer-specified distances, completely disrupt the reception of GNSS signals. Their impact is also evident at greater distances, where they significantly reduce SNR values, increase DOP, and decrease the number of visible satellites, leading to reduced measurement reliability and integrity. These results underline the necessity of developing effective protection mechanisms against GNSS interference and strategies to ensure reliable signal reception in GNSS-dependent applications, particularly as the use of jamming devices becomes more prevalent.

CROPOS, as the Croatian GNSS network, was modernized and upgraded to support the Galileo system in 2019. Two of CROPOS’s services—VPPS (Network RTK service) and GPPS (post-processing service)—were assessed for the contribution of the Galileo system to their performance. A station used for field testing was previously examined and surveyed to determine the local horizon and to carry out a detailed mission planning. The whole day of observation was divided into several sessions, each with a different visibility of Galileo satellites. A special observation sequence was designed: VPPS (GPS-GLO-GAL), VPPS (GAL-only), and GPPS (GPS-GLO-GAL-BDS). All observations were taken on the same station with the same GNSS receiver, Trimble R12. Each static observation session was post-processed in Trimble Business Center (TBC) in two different ways: considering all available systems (GGGB) and considering GAL-only observations. A daily static solution based on all systems (GGGB) was considered as the reference for the accuracy assessment of all obtained solutions. The results obtained with VPPS (GPS-GLO-GAL) and VPPS (GAL-only) were analyzed and assessed; the results obtained with GAL-only have shown a slightly higher scatter. It was concluded that the inclusion of the Galileo system in CROPOS has contributed to the availability and reliability of solutions but not to their accuracy. By complying with the observation rules and taking redundant measurements, the accuracy of GAL-only results can be improved.

The CROPOS’s ZAGR stations, one of 33 stations of the Croatian permanent GNSS (Global Navigation Satellite System) network CROPOS (Croatian Positioning System), is located in Zagreb’s city centre. For the first time, motion of one of the CROPOS stations (the ZAGR station) during an earthquake shake (the Zagreb 2020 ML5.5) was analysed by the PPK (Post-Processed Kinematic) method using all available GNSS signals (GPS – Global Positioning System, GLONASS – GLObalnaya NAvigatsionnaya Sputnikovaya Sistem, Galileo, Bei-Dou) and seismologically interpreted. The ZAGR station is situated about 9 km to the south-southeast of the earthquake’s epicentre. The analysis showed that the station’s movements, i.e. combined surface and building motion, during the shake was far above the noise level and enabled the assessment of the station’s kinematics: movements in the range of approx. 13 cm in direction north–south (N–S) and approx. 6 cm in direction east–west (E–W). However, movements in the vertical direction were slightly above the noise level. Even though the ZAGR station kinematic behaviour was pronounced, no permanent displacement was identified. The seismological analysis showed that the ZAGR station recorded the onset of the SV-waves on the N–S component, surface waves on the N–S (predominantly Rayleigh waves) and E–W (mainly Love waves) components. The resolution of 1 s of the results of the PPK method have enabled a thorough analysis of the ZAGR station kinematics and pointed out the usefulness of the method in earthquake observations.

Within the Croatian-Hungarian project for the first time in the Republic of Croatia the repeat stations survey was carried out using an onsite dIdD (delta Declination / delta Inclination) variometer. Since the geomagnetic field vector...