GNSS Stations Research Articles

Response Analysis on Multi‐Parameters in the 2022 Tonga Volcanic Eruption Using Satellite‐Ground Combined Data

AbstractThe Tonga volcano (TVE) erupted with a mass of energy released into the plate and atmosphere, causing variations in the relevant geophysical parameters. Thus, we creatively apply the observations from space‐borne and ground‐based sensors to reveal the characterizations of up to four items (tropospheric response, sea surface temperature (SST), surface deformation, and ionospheric reaction). The results of precipitable water vapor from space‐borne and ground‐based data show that tropospheric response has a trend of rising first, after the volcano event dropping sharply, then recovering to the normal level. The reaction of SST shows a slight rise of 0.5–1°C caused by the incident. Examining ground‐based Global Navigation Satellite System station coordinates illustrates that the volcano eruption causes surface deformations up to 46 cm in the northeast direction. Eventually, for the ionospheric reaction, a similar characterization of the tropospheric response is found in the total electron content variation. These are the first comprehensive analyses showing the impacts of the TVE on multiple types of parameters using both space‐borne and ground‐based data from low to high frequency.

Limited Shallow Slip for the 2020 Simeonof Earthquake, Alaska, Constrained by GNSS‐Acoustic

AbstractThe 22 July 2020 Mw7.8 Simeonof earthquake was a deep megathrust event that ruptured along the Shumagin segment of the Alaska‐Aleutian subduction zone. This earthquake occurred ∼250 km from a seafloor geodetic GNSS‐Acoustic site IVB1, where we observed a velocity of 3.78 ± 1.15 cm/yr with the down‐going slab prior to the earthquake followed by 0.6 ± 0.7 eastward and −15.5 ± 0.8 cm northward coseismic offset. We computed a slip model of the coseismic rupture using the static offset at IVB1 alongside regional continuous GNSS and strong motion stations. The small static horizontal offset at the site precludes significantly shallower rupture than previously inferred from terrestrial observations, confirming that the Simeonof earthquake was a deep megathrust earthquake. The observed site velocity implies partial locking prior to the earthquake, implying significant shallow strain accumulation such that the small coseismic offset is unlikely to have relieved all of the accumulated strain since the last coseismic rupture.

Ionospheric scintillation characteristics over Indian region from latitudinally-aligned geodetic GPS observations

Ionospheric scintillations pose one of the biggest threats to Satellite-Earth communication links in the communication and navigation systems services whose occurrence characteristics could be explained through the strength of fading (amplitude scintillation index; S4) and the rapidity of the fades (decorrelation time; \U0001d70f0). In the present work, we analyzed the S4 index from a latitudinal array of three geodetic global positioning system (GPS) stations along the Indian longitude sector during the descending phase of the 24th solar cycle. The results show predominant occurrences of scintillations during the post-sunset and nighttime periods indicating the level of scintillations close to equatorial, beyond anomaly crest, and near mid-latitude locations. The strong amplitude scintillations during 2014 and 2015 and their lowest magnitudes during 2016 and 2017 reflect the solar activity dependence of the scintillation occurrences. The directional distribution and 2-dimensional surface sky plots of the S4 index substantiate the occurrence of intense scintillation being more prevalent towards the equatorial location, whereas the weak and moderate scintillations are perceived towards the higher low latitude stations. The occurrences of intense scintillations are confirmed in high solar active years and equinox season at all stations, while the equatorial station presents relatively higher occurrences in winter followed by summer. The summer season witnessed intense occurrences even under moderate to low solar activity years (2016–2017), reflecting the post-midnight occurrences due to meridional thermospheric winds. Moreover, maximum percentage occurrences of weak scintillations in all seasons are evident towards the poleward side, far away from the anomaly crest. The amplitude scintillation frequency during the period is further compared with the solar and geomagnetic indices to substantiate the analysis drawn from the variations. The correlation coefficients between the scintillation index occurrence rate with the solar and geomagnetic in-dices at three GNSS stations provide valuable insights into the relationship between solar activity and scintillation. The results show that the strength and direction of the correlation can vary significantly depending on the specific solar index and location. Thus, emphasize further studies on scintillation occurrences for developing effective forecasting and mitigation models over the Indian low-latitude region.

The Seasonal Variations Analysis of Permanent GNSS Station Time Series in the Central-East of Europe

Observations from permanent GNSS stations are actively used for the research and monitoring of geodynamic processes. Today, with the use of modern scientific programs and IGS products, it is possible to determine GNSS station coordinates and velocities at the level of a few millimeters. However, the scientific community constantly faces the question of increasing the accuracy of coordinate definitions to obtain more reliable data in the study of geodynamic phenomena. One of the main sources of errors is systematic measurement errors. To date, the procedure for their removal is still incomplete and imperfect. Also, during the processing of long-term GNSS measurements, it was found that the coordinate time series, after the removal of trend effects, are also characterized by seasonal variations, mainly of annual and semi-annual periods. We estimated the daily coordinate time series of 10 permanent GNSS stations in the central-eastern part of Europe from 2001 to 2019 and calculated the seasonal variation coefficients for these stations. The average value of the coefficients for the annual cycle for the N, E, and H components is −0.7, −0.2, and −0.7 mm, and for the semi-annual cycle the average value is 0.3, 0.4, and −0.5 mm. The obtained coefficients are less than 1 mm, which is why it can be argued that there is no seasonal component in the coordinate time series or that it is so small that it is a problematic task to calculate it. This practical absence of a seasonal component in long-term time series of GNSS coordinates, in our opinion, is partly compensated by the use of modern models of mapping functions (such as VMF3) for zenith tropospheric delays instead of the empirical GMF. To test the obtained results, we calculated the coefficients of seasonal variations for the sub-network of GNSS stations included in the category of the best EPN stations—C0 and C1. The values of the coefficients for the stations of this network are also less than 1 mm, which confirms the previous statement about the absence of a seasonal component in the long-term time series of coordinates. We also checked the presence of seasonal changes in the time series using the well-known decomposition procedure, which showed that the seasonal component is not observed because the content does not exceed 10% for additive decomposition and 20% for multiplicative decomposition.

A MATLAB toolbox for computation of velocity and strain rate field from GNSS coordinate time series

We propose a MATLAB toolbox for the computation of the strain rate field from the coordinate time series of some continuous GNSS stations. It consists of several functions, also compatible with GNU Octave, implementing the following steps: (i) time series download from a data repository (e.g., the Nevada Geodetic Laboratory database); (ii) calculation of velocities of the selected stations by means of the Maximum Likelihood Estimation (MLE) method implemented in the external package Hector, including modeling of offsets, outliers, noise and periodic components; (iii) (optional) filtering of Common Mode Errors; (iv) calculation of the strain rate field with the modified least squares method, in which a scale factor can be introduced to define the locality of the deformation analysis and, besides uncertainty estimation, a geometric evaluation of the significance of the results is provided; (v) visualization of the results for immediate use and easy interpretation for scientific purposes. The toolbox is divided into two components: the first one, named StaVel, performs the steps (i)-(iii) and the second component, GridStrain, performs the steps (iv) and (v). The potential of the toolbox is demonstrated on a real dataset. Time series from several continuous GNSS stations in South-Eastern Sicily (Southern Italy) are processed by means of StaVel and GridStrain in order to provide the strain rate field.

Relation Between Oceanic Plate Structure, Patterns of Interplate Locking and Microseismicity in the 1922 Atacama Seismic Gap

AbstractWe deployed a dense geodetic and seismological network in the Atacama seismic gap in Chile. We derive a microseismicity catalog of >30,000 events, time series from 70 GNSS stations, and utilize a transdimensional Bayesian inversion to estimate interplate locking. We identify two highly locked regions of different sizes whose geometries appear to control seismicity patterns. Interface seismicity concentrates beneath the coastline, just downdip of the highest locking. A region with lower locking (27.5°S–27.7°S) coincides with higher seismicity levels, a high number of repeating earthquakes and events extending toward the trench. This area is situated where the Copiapó Ridge is subducted and has shown previous indications of both seismic and aseismic slip, including an earthquake sequence in 2020. While these findings suggest that the structure of the downgoing oceanic plate prescribes patterns of interplate locking and seismicity, we note that the Taltal Ridge further north lacks a similar signature.

An Improved VMD-LSTM Model for Time-Varying GNSS Time Series Prediction with Temporally Correlated Noise

GNSS time series prediction plays a significant role in monitoring crustal plate motion, landslide detection, and the maintenance of the global coordinate framework. Long short-term memory (LSTM) is a deep learning model that has been widely applied in the field of high-precision time series prediction and is often combined with Variational Mode Decomposition (VMD) to form the VMD-LSTM hybrid model. To further improve the prediction accuracy of the VMD-LSTM model, this paper proposes a dual variational modal decomposition long short-term memory (DVMD-LSTM) model to effectively handle noise in GNSS time series prediction. This model extracts fluctuation features from the residual terms obtained after VMD decomposition to reduce the prediction errors associated with residual terms in the VMD-LSTM model. Daily E, N, and U coordinate data recorded at multiple GNSS stations between 2000 and 2022 were used to validate the performance of the proposed DVMD-LSTM model. The experimental results demonstrate that, compared to the VMD-LSTM model, the DVMD-LSTM model achieves significant improvements in prediction performance across all measurement stations. The average RMSE is reduced by 9.86% and the average MAE is reduced by 9.44%; moreover, the average R2 increased by 17.97%. Furthermore, the average accuracy of the optimal noise model for the predicted results is improved by 36.50%, and the average velocity accuracy of the predicted results is enhanced by 33.02%. These findings collectively attest to the superior predictive capabilities of the DVMD-LSTM model, thereby demonstrating the reliability of the predicted results.

The Relationship of Time Span and Missing Data on the Noise Model Estimation of GNSS Time Series

Accurate noise model identification for GNSS time series is crucial for obtaining a reliable GNSS velocity field and its uncertainty for various studies in geodynamics and geodesy. Here, by comprehensively considering time span and missing data effect on the noise model of GNSS time series, we used four combined noise models to analyze the duration of the time series (ranging from 2 to 24 years) and the data gap (between 2% and 30%) effects on noise model selection and velocity estimation at 72 GNSS stations spanning from 1992 to 2022 in global region together with simulated data. Our results show that the selected noise model have better convergence when GNSS time series is getting longer. With longer time series, the GNSS velocity uncertainty estimation with different data gaps is more homogenous to a certain order of magnitude. When the GNSS time series length is less than 8 years, it shows that the flicker noise and random walk noise and white noise (FNRWWN), flicker noise and white noise (FNWN), and power law noise and white noise (PLWN) models are wrongly estimated as a Gauss–Markov and white noise (GGMWN) model, which can affect the accuracy of GNSS velocity estimated from GNSS time series. When the GNSS time series length is more than 12 years, the RW noise components are most likely to be detected. As the duration increases, the impact of RW on velocity uncertainty decreases. Finally, we show that the selection of the stochastic noise model and velocity estimation are reliable for a time series with a minimum duration of 12 years.

Effects of 7September 5–12, 2017 solar flares on regional disturbance of Earth’s ionosphere as recorded by GNSS stations located in the Volga Federal District of the Russian Federation

The paper presents the results of estimation of the effects of September 5–12, 2017 solar flares on the regional disturbance of Earth's ionosphere according to data from a distributed network of GNSS stations located mostly in the Volga Federal District of the Russian Federation. The GNSS data processing software package we have developed is used to analyze recorded signal power and daily two-frequency phase measurements, as well as to calculate the total electron content and map the data. The results of the study show that during powerful solar flares X2.2 and X9.3 on September 6 the median value of the total electron content, calculated for the Volga Federal District, increased up to 0.25 TECU and 0.6 TECU respectively. At that time, the region of interest (40°–55° E) was sunlit. The prolonged magnetic storms on September 8 also generated noticeable ionospheric disturbances up to 0.2 TECU. At the same time, neither the solar flares nor the magnetic storms had a significant effect on the power characteristics of the recorded signals from navigation satellites in the region under study. The median carrier-to-noise ratio calculated for the region considered over the entire observation period did not differ from the values recorded under undisturbed ionospheric conditions and varied between 47–53 dBHz and 38–49 dBHz for frequencies L1 and L2 respectively.

Влияние солнечных вспышек 5-12 сентября 2017 г. на региональную возмущенность ионосферы Земли по данным ГНСС-станций, расположенных в Приволжском федеральном округе Российской Федерации

The paper presents the results of estimation of the effects of September 5–12, 2017 solar flares on the regional disturbance of Earth's ionosphere according to data from a distributed network of GNSS stations located mostly in the Volga Federal District of the Russian Federation. The GNSS data processing software package we have developed is used to analyze recorded signal power and daily two-frequency phase measurements, as well as to calculate the total electron content and map the data. The results of the study show that during powerful solar flares X2.2 and X9.3 on September 6 the median value of the total electron content, calculated for the Volga Federal District, increased up to 0.25 TECU and 0.6 TECU respectively. At that time, the region of interest (40°–55° E) was sunlit. The prolonged magnetic storms on September 8 also generated noticeable ionospheric disturbances up to 0.2 TECU. At the same time, neither the solar flares nor the magnetic storms had a significant effect on the power characteristics of the recorded signals from navigation satellites in the region under study. The median carrier-to-noise ratio calculated for the region considered over the entire observation period did not differ from the values recorded under undisturbed ionospheric conditions and varied between 47–53 dBHz and 38–49 dBHz for frequencies L1 and L2 respectively.

On the improvement of the sensitivity levels of VLBI solutions from a combination with GNSS

Very Long Baseline Interferometry (VLBI) is the only technique that connects the celestial and the terrestrial reference frames. Because of its essential role, it is important to investigate the quality of VLBI observations and their effect on the estimated parameters. The fundamental goal of the quality assessment using the sensitivity is to find out to what level VLBI can detect station displacements in the adjusted coordinates. However, the global VLBI station network is worse in terms of the number and global distribution of stations when compared to the GNSS station network. In this study, we aim to improve the capacity of VLBI to detect station displacements through an inter-technique combination with GNSS. The effect of the selection of co-location sites in the inter-technique combination is investigated with four scenarios and we investigate how the sensitivity is affected by the assumed standard deviations of the local ties. The lower the standard deviations of the local ties, the higher the obtained sensitivity level. When larger standard deviations are assumed, the sensitivity levels of the VLBI stations are obtained up to 3 mm. When a smaller deviation is assumed for a local tie having various standard deviations obtained from different local tie observations, the sensitivity levels change too. If local ties with standard deviations of 1 cm and more are excluded, the detection capacities of the VLBI stations based on the gross errors improve by around 1 mm. When smaller standard deviations are assumed among the local ties, which are used in the inter-technique combination, the sensitivity levels drop below 2 mm. Hence, this study quantifies how important the selection of the co-location sites and the standard deviations of the local ties are for the accuracy of geodetic products obtained by inter-technique combination.

Geodetic constraints on contemporary three-dimensional crustal deformation in the Laji Shan–Jishi Shan tectonic belt

The Laji Shan–Jishi Shan tectonic belt (LJTB), located in the southern part of the northeastern Tibetan Plateau (NETP), is a tectonic window to reveal regional tectonic deformation in the NETP. However, its kinematics in the Holocene remains controversial. We obtain the latest and dense horizontal velocity field based on data collected from our newly constructed and existing GNSS stations. Combined with fault kinematics from geologic observations, we analyze the crustal deformation characteristics along the LJTB. The results show that: (1) The Laji Shan fault (LJF) is inactive, and the northwest-oriented Jishi Shan fault (JSF) exhibits a significant dextral and thrust slip. (2) The transpression along the arc-shaped LJTB accommodates deformation transformation between the dextral Riyue Shan fault and the sinistral west Qinling fault. (3) With the continuous pushing of the Indian plate, internal strains in the Tibetan Plateau are continuously transferred in the northeast via the LJTB as they are gradually dissipated near the LJTB and translated into significant crustal uplift in these regions.

Geodynamic Studies in the Pieniny Klippen Belt in 2004–2020

ABSTRACT The Pieniny Geodynamic Test Field is situated in the middle of the region between the Inner and Outer Carpathians. Geodynamic research conducted in the past in the Pieniny Klippen Belt (PKB) region were suggestive of neotectonic activity. The goal of the investigation was to determine whether the nearby structures, the Podhale Flysh (FP) and the Magura Nappe (MN), are affected by neotectonic activity in the PKB. The goal of the study was to ascertain the velocity and direction of motion of stations situated close to the Pieniny Geodynamic Test Field’s 3 main structures. Twelve GNSS stations, including 6 in the PKB, 3 in the MN, and 3 in the FP, make up the Pieniny Geodynamic Test Field. Three GNSS sites in the Tatra Mountains (TM) complete the entire geodynamic test field. The satellite observations made between 2004 and 2020 (excluding the year 2005 due to lack of observation) were investigated to identify the horizontal movements. Using the IGb14 reference system, the station’s positions and velocities were calculated. First, daily sessions were used to process the horizontal coordinates of the points for an average observation epoch in a given year. Sixteen measurement epochs were included in the long-time solution. Based on the horizontal velocity residues in the north–south and east–west directions, the station’s movement was calculated. The collected results were compared to information from the EUREF Permanent GNSS Network (EUREF) and to the findings of prior research on the tectonic activity of the PKB. The results of horizontal displacements calculated using GNSS measurements in the area of the PKB and nearby structures—the MN and the FP are presented and analyzed in this article.

Seismicity modulation due to hydrological loading in a stable continental region: a case study from the Jektvik swarm sequence in Northern Norway

SUMMARYSeismic swarms have been observed for more than 40 yr along the coast of Nordland, Northern Norway. However, the detailed spatio-temporal evolution and mechanisms of these swarms have not yet been resolved due to the historically sparse seismic station coverage. An increased number of seismic stations now allows us to study a nearly decade-long sequence of swarms in the Jektvik area during the 2013–2021 time window. Our analysis resolves four major groups of seismic events, each consisting of several spatial clusters, that have distinct spatial and temporal behaviours. Computed focal mechanism solutions are predominantly normal with NNE–SSW strike direction reflecting a near-vertical maximum principal stress and a NW–SE near-horizontal minimum principal stress, which are controlled by local NW–SE extension. We attribute the swarms to fluid-saturated fracture zones that are reactivated due to this local extension. Over the time period, the activity tends to increase between February and May, which coincides with the late winter and beginning of spring time in Norway. We hypothesize that the seismicity is modulated seasonally by hydrological loading from snow accumulation. This transient hydrological load results in elastic deformation that is observed at local Global Navigation Satellite System stations. The loading is shown to promote failure in a critically stressed normal faulting system. Once a segment is activated, it can then also trigger neighboring segments via stress transfer. Our new results point to a close link between lithosphere and hydrosphere contributing to the occurrence of seismic swarm activity in northern Norway.

Assessment of GNSS stations using atmospheric horizontal gradients and microwave radiometry

We have assessed the quality of four co-located GNSS stations by studying time series of estimated linear horizontal gradients in the signal delay. The stations have different electromagnetic environments. We also examine the consistency of the results by using two different GNSS softwares, GipsyX and c5++, and applying three different elevation cutoff angles: 5°, 10°, and 20°. The estimated gradients are compared with the corresponding ones estimated from microwave radiometer observations acquired during six months (April–September 2021). For all four stations and using both softwares we find that is is possible to track gradient variations over time scales from less than one hour using GPS observations only. We have indications that it is an advantage to equip the area below the GNSS antenna with microwave absorbing material. However, the differences are small, a reduction in rms differences in the gradients compared to those from the microwave radiometer of less than 2 %. More studies are needed to decide if such an investment is reasonable in terms of cost and maintenance.

Regional Tropospheric Correction Model from GNSS–Saastamoinen–GPT2w Data for Zhejiang Province

Tropospheric delay models based on GNSS observations are essential for studying tropospheric changes. However, the uneven distribution of GNSS stations reduces the accuracy of GNSS tropospheric delay models in remote areas. Moreover, the accuracy of the tropospheric delay calculated by traditional models, which rely on meteorological parameters, is lower compared to the accuracy achieved by GNSS tropospheric models. At present, there are sufficient surface meteorological observation facilities around the world that can obtain surface meteorological parameters in real time. It is of great importance to make full use of the measured meteorological parameters to establish tropospheric correction models. Moreover, the empirical tropospheric models use free and open data, and one can obtain tropospheric parameters through the model without requiring any auxiliary information. We established a provincial real-time regional tropospheric fusion model using ground-based GNSS observations, a meteorological model, and empirical model data. Results showed that the tropospheric delay observations of the three models can be fused to establish a real-time tropospheric delay model with better accuracy and higher spatiotemporal resolution. The accuracy of Zenith Total Delay (ZTD) estimated by the fusion model reached 0.96/1.04/3.11 cm during the tropospheric quiet/active/typhoon period.

MATHEMATICAL AND PHYSICAL APPROACHES TO INFER ABSOLUTE ZENITH WET DELAYS FROM DOUBLE DIFFERENTIAL INTERFEROMETRIC OBSERVATIONS USING ERA5 ATMOSPHERIC REANALYSIS

Abstract. Atmospheric water vapor (WV) is one of the driving constituents of the atmosphere. The modelling and forecasting of WV and derived quantities like precipitable water is reliable on regional scales but challenging on small scales because of its high spatial and temporal variation. Interferometric synthetic aperture radar (InSAR) can be exploited to retrieve integrated atmospheric water vapor (IWV) from path delay observations along the radar line of sight. InSAR-derived IWV maps feature a very high spatial resolution but the double-differential interferometric observations only provide changes of IWV between acquisition times and with respect to a certain spatial reference. In this study we present a method to derive the absolute IWV by combining ERA5 numerical weather model data with differential path delay observations from InSAR time series. We propose different functional approaches to merge the regional trend of WV from ERA5 with the high resolution IWV signal from InSAR. We apply this to a Sentinel-1 Persistent Scatterer InSAR time series in the Upper Rhine Graben and validate against IWV observations at GNSS stations of the Upper Rhine Graben Network.

Analysis of GNSS Data for Earthquake Precursor Studies Using IONOLAB-TEC in the Himalayan Region

Earthquake precursors are the indicators that appear before an earthquake. The release of radon gas, ionospheric disturbances, anomalous animal behavior, and so on are examples of seismic and aseismic events. Ionospheric perturbations can be proved to be a reliable method in earthquake prediction. The GNSS data detect changes in the ionosphere through the time lag of the transmitted GPS signals recorded at the Earth-based receivers. A negative TEC anomaly is caused by the stress released from the rocks before the earthquake, which elevates positive ions or p-holes in the atmosphere and decreases the ions in the ionosphere. A positive TEC anomaly follows this because of the increase in ions in the ionosphere. The ionospheric disruption in the Himalayan region is examined before five random earthquakes. For this, data from 15 separate GNSS stations are investigated using IONOLAB-TEC. A promising total electron content (TEC) data estimate with a temporal resolution of 30 s was analyzed. The results of the TEC data analysis depict the anomaly a month before the five earthquakes, followed by the later perturbation in the earthquake preparation zone. TEC anomalies are enhanced more by the uniform spatial distribution of GNSS stations in the epicentral region than by randomly distributed stations. The results of IONOLAB-TEC and the widely used GPS-TEC software were compared. Owing to its temporal resolution, IONOLAB-TEC has edge over the GPS-TEC software in that it can identify even the slightest negative anomalies before an earthquake.

Sea Tide Influence on Ice Flow of David Drygalski’s Ice Tongue Inferred from Geodetic GNSS Observations and SAR Offset Tracking Analysis

David Glacier and Drygalski Ice Tongue are massive glaciers in Victoria Land, Antarctica. The ice from the East Antarctic Ice Sheet is drained through the former, and then discharged into the western Ross Sea through the latter. David Drygalski is the largest outlet glacier in Northern Victoria Land, floating kilometers out to sea. The floating and grounded part of the David Glacier are the main focus of this article. During the XXI Italian Antarctic Expedition (2005–2006), within the framework of the National Antarctic Research Programme (PNRA), two GNSS stations were installed at different points: the first close to the grounding line of David Glacier, and the second approximately 40 km downstream of the first one. Simultaneous data logging was performed by both GNSS stations for 24 days. In the latest data processing, the kinematic PPP technique was adopted to evaluate the dominant diurnal components and the very small semi-diurnal variations in ice motion induced by the ocean tide and the mean ice flow rates of both GNSS stations. Comparison of the GNSS time series with predicted ocean tide calculated from harmonic coefficients of the nearest tide gauge stations, installed at Cape Roberts and Mario Zucchelli Station, highlight different local response of the glacier to ocean tide, with a minor amplitude of vertical motion at a point partially anchored at the bedrock close to the grounding line. During low tide, the velocity of the ice flow reaches its daily maximum, in accordance with the direction of seawater outflow from the fjord into the ocean, while the greatest daily tidal excursion generates an increase in the horizontal ice flow velocity. With the aim to extend the analysis in spatial terms, five COSMO-SkyMED Stripmap scenes were processed. The comparison of the co-registered offset tracking rates, obtained from SAR images, with the GNSS estimation shows good agreement.

Визначення еталонних напрямків на сертифікованому поліґоні з використанням GNSS вимірювань

The relevance of PPP technology has greatly increased over the past 10 years. While the centimeter level of accuracy has already been practically ensured in most spheres of economic activity, first of all, in geodesy, the millimeter level for scientific tasks related to the study of the influence of geophysical factors on the environment is still the subject of research. The purpose of this work is to identify the real accuracy of the modification of the PPP-AR method using the example of data from four permanent GNSS stations: SULP (Lviv), FRAN (Ivano-Frankivsk), RAHI (Rakhiv), TERN (Ternopil), included in the European the EPN network (EUREF Permanent GNSS Network). Method. To fulfill the given task, we used data from four permanent GNSS stations. 3 weeks of observations were processed: one in July (2217 GPS week), one in August (2222 GPS week) and one in September (2226 GPS week). Processing of the observation files was carried out in the PRIDE PPP-AR software environment, which was pre-installed on the server with the Ubuntu operating system. The coordinates of each station were calculated with the same input parameters, namely, taking into account the second-order ionospheric correction and the function of displaying inclined zenith delays of signals from satellites in the direction of the VMF3 zenith. We compared the obtained sets of coordinates with the control coordinates of these stations. For the time periods we chose, the coordinates calculated by the relative method based on the formation of phase differences in the combined EPN processing center were taken as control. The results. The main results of our research were the difference of coordinates (comparison of the received coordinates with control ones). For each station, the obtained differences are unidirectional in nature and vary little between stations. The average value of the coordinate differences was from 0.6 to 7.2 mm and practically does not depend on the processing time interval. The root mean square error (RMS) of the coordinate differences is at the level of 1.5 – 3 mm and also changes little over time. It was found that the accuracy of determining the coordinates based on the processing of GNSS measurement data at permanent stations SULP, TERN, FRAN, RAHI using the PPP-AR method is quite high, but a systematic difference of several millimeters is noticeable, which may be caused by insufficient consideration of some factors of geophysical origin . Scientific novelty and practical significance. It is shown that the PPP-AR method at the current stage of development of GNSS technologies achieves the accuracy of the coordinate determination method based on phase differences and can be applied not only in geodesy tasks, but also in geodynamic studies, provided the results of daily GNSS observations are used. A promising direction for further research is the identification of unaccounted sources of systematic errors.