GNSS Measurements Research Articles

A new technical pathway for extracting high accuracy surface deformation information in coal mining areas using UAV LiDAR data: An example from the Yushen mining area in western China

Western China is the world’s major coal-producing area, accounting for 1/3 of global coal production. Large-scale underground coal mining has led to serious ground deformation that has unique spatial and temporal characteristics. However, there are obvious engineering limitations to using GNSS, InSAR, and other common measurement techniques for monitoring mining subsidence. In recent years, researchers have attempted to use UAV LiDAR to monitor subsidence in mining areas. Point clouds are obtained through periodic ground scanning. Surface subsidence information is extracted through the filtering, modeling, and superposition processes. Conventional point cloud processing usually produces subsidence models that are too noisy and only provide information on surface subsidence. This means that it is unable to capture the horizontal ground displacement accompanying subsidence in mining areas, which hinders the practical application of this technology. A local flat point extraction (LFPE) algorithm based on geomorphic features is proposed. The algorithm extracts flat surface point clouds from the scan data and calculates the precise subsidence value of the ground by superposition to facilitate deformation monitoring. The obtained subsidence volume is spatially interpolated based on the unique spatial distribution characteristics of the mining subsidence basin to generate the initial surface subsidence model. By denoising this model, we can obtain a fine surface subsidence model that avoids significant noise caused by non-ground point clouds participating in modeling and superposition in common processing methods. On this basis, we successfully extracted the horizontal displacement information accompanying subsidence by employing sub-pixel correlation using the surface feature images before and after subsidence. The proposed technical pathway was validated by applying it to a coal mining subsidence area in the Yushen mining area in western China. Results demonstrate that, compared to conventional treatments, the proposed subsidence modeling method using laser scanning point clouds improves monitoring accuracy by over 50% while also obtaining the necessary horizontal displacement information for engineering requirements. These findings confirm the efficiency and accuracy of the proposed method for acquiring 3D surface deformation in mining areas.

A Novel Method of Ionospheric Inversion Based on Horizontal Constraint and Empirical Orthogonal Function

Tomographic inversion of the ionosphere is a rank-deficient problem. To overcome the above problem, an algebraic reconstruction technique (ART) based on adaptive horizontal constraint and empirical orthogonal function (ARTHCEOF) is proposed. The new algorithm avoids the difficulty of vertically constrained matrix construction and resolves the description of the ionospheric vertical structure by using EOF. To confirm the feasibility and validate the ascendancy of the ARTHCEOF, three algorithms are first tested by using the emulated scheme. The test results show that the ARTHCEOF surpasses the ART and the ART based on the horizontal constraint (ARTHC) in both the inversion accuracy and computational efficiency. Finally, the ARTHCEOF method is applied to invert electron density values using the GNSS measurements during different geomagnetic activities. The tomographic images validate that the ARTHCEOF can reflect ionospheric daily changes in the European region. The altitudinal profiles in a fixed location are illustrated according to the inversion results of ARTHCEOF. Compared with the profiles recorded by the ionosonde station, the altitudinal profiles of ARTHCEOF have a good consistency. In the meantime, the VTEC values are inverted using the CIT results. The differential VTEC values are calculated by means of the inverted VTEC values and ionospheric products of CODE. The differential results further identify the dependability of ARTHCEOF.

Monitoring Strategy of Geological Hazards Using Integrated Three-dimensional InSAR and GNSS Technologies with Case Study

Geodetic/geodynamic benchmarks, equipped with both ascending and descending radar corner reflectors, and a method for integrated InSAR and GNSS/GPS network observation were developed and applied as the continuation of the former geodetic monitoring at the Dunaszekcső landslide, Hungary. The attempts to apply InSAR technologies using archive and Sentinel-1 data practically failed on the most intensive landside areas (“Vár” and “Szent János” hills), where proper persistent or distributed scatterers were not found. Our concept solved this problem, where the Simple Look Complex (SLC) images are used to interpolate the movements between two GNSS network observations using the integrated benchmarks and the method of Kalman-filtering. Since the InSAR line-of-sight (LOS) changes are barely sensitive to the north movements, this information is essentially provided by GNSS measurement alone, moreover, the GNSS measurements are used to: a) identify the benchmarks, b) detect the unwrapping errors and missing cycles and c) provide the boundary values of Kalman-filtering.After the installation of benchmarks three GPS observations were carried out and 69 ascending and 61 descending Sentinel-1 A and B images were processed. The data processing properly indicated the general movement history, which fit the curves of former geodetic observations, as well. The dense data points of the East and Up (vertical) components made possible more detailed geomorphologic interpretations of the ongoing process between two GPS observations. During the investigated periods the deceleration of movements was experienced, however, the deceleration of the dormant state needs the continuation of the monitoring.

An Improved Ambiguity Resolution Algorithm for Smartphone RTK Positioning.

Ambiguity resolution based on smartphone GNSS measurements can enable various potential applications that currently remain difficult due to ambiguity biases, especially under kinematic conditions. This study proposes an improved ambiguity resolution algorithm, which uses the search-and-shrink procedure coupled with the methods of the multi-epoch double-differenced residual test and the ambiguity majority tests for candidate vectors and ambiguities. By performing a static experiment with Xiaomi Mi 8, the AR efficiency of the proposed method is evaluated. Furthermore, a kinematic test with Google Pixel 5 verifies the effectiveness of the proposed method with improved positioning performance. In conclusion, centimeter-level smartphone positioning accuracy is achieved in both experiments, which is greatly improved compared with the float and traditional AR solutions.

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.

SMARTPHONE LEVEL INDOOR/OUTDOOR UBIQUITOUS PEDESTRIAN POSITIONING 3DMA GNSS/VINS INTEGRATION USING FGO

Abstract. This paper discusses ubiquitous smartphone pedestrian positioning challenges in urban canyons and GNSS-denied areas such as indoor spaces. Existing sensor-based techniques, including GNSS, INS, and VIO, have limitations that affect positioning accuracy and reliability. A machine learning-based approach is suggested to employ Support Vector Machine (SVM) to classify indoor/outdoor (IO) detection using GNSS measurement data. The proposed system integrates local estimates on VIO and 3D mapping aided (3DMA) GNSS measurements using Factor Graph Optimization (FGO) with an IO detection switch to estimate precise pose and eliminate global drift. The effectiveness of the system is evaluated through real-world experiments that produce notable outcomes.

InSAR‐Derived Horizontal Velocities in a Global Reference Frame

AbstractInterferometric Synthetic Aperture Radar is used to measure deformation rates over continents to constrain tectonic processes. The resulting velocity measurements are only relative, however, due to unknown integer ambiguities introduced during propagation of the signal through the atmosphere. These ambiguities mostly cancel when using spectral diversity to estimate along‐track motion, allowing measurements to be made with respect to a global reference frame. Here, we calculate along‐track velocities for a partial global data set of Sentinel‐1 acquisitions and find good agreement with ITRF2014 plate motion model and measurements from GPS stations. We include corrections for solid‐earth tides and gradients of ionospheric total electron content. Combining data from ascending and descending orbits we are able to estimate north and east velocities over 250 × 250 km areas and their accuracy of 4 and 23 mm/year, respectively. These “absolute” measurements can be particularly useful for global velocity and strain rate estimation where GNSS measurements are sparse.

Plasma bubble imaging by single-frequency GNSS measurements

Plasma bubble imaging by single-frequency GNSS measurements

A Redundant Measurement-Based Maximum Correntropy Extended Kalman Filter for the Noise Covariance Estimation in INS/GNSS Integration

The resolution accuracy of the inertial navigation system/global navigation satellite system (INS/GNSS) integrated system would be degraded in challenging areas. This paper proposed a novel algorithm, which combines the second-order mutual difference method with the maximum correntropy criteria extended Kalman filter to address the following problems (1) the GNSS measurement noise estimation cannot be isolated from the state estimation and suffers from the auto-correlated statistic sequences, and (2) the performance of EKF would be degraded under the non-Gaussian condition. In detail, the proposed algorithm determines the possible distribution of the measurement noise by a kernel density function detection, then depending on the detection result, either the difference sequences–based method or an autoregressive correction algorithm’s result is utilized for calculating the noise covariance. Then, the obtained measurement noise covariance is used in MCEKF instead of EKF to enhance filter adaptiveness. Meanwhile, to enhance the numerical stability of the MCEKF, we adopted the Cholesky decomposition to calculate the matrix inverse in the kernel function. The road experiment verified that our proposed method could achieve more accurate navigation resolutions than the compared ones.

An ROI Optimization Method Based on Dynamic Estimation Adjustment Model

An important research direction in the field of traffic light recognition of autonomous systems is to accurately obtain the region of interest (ROI) of the image through the multi-sensor assisted method. Dynamic evaluation of the performance of the multi-sensor (GNSS, IMU, and odometer) fusion positioning system to obtain the optimum size of the ROI is essential for further improvement of recognition accuracy. In this paper, we propose a dynamic estimation adjustment (DEA) model construction method to optimize the ROI. First, according to the residual variance of the integrated navigation system and the vehicle velocity, we divide the innovation into an approximate Gaussian fitting region (AGFR) and a Gaussian convergence region (GCR) and estimate them using variational Bayesian gated recurrent unit (VBGRU) networks and a Gaussian mixture model (GMM), respectively, to obtain the GNSS measurement uncertainty. Then, the relationship between the GNSS measurement uncertainty and the multi-sensor aided ROI acquisition error is deduced and analyzed in detail. Further, we build a dynamic estimation adjustment model to convert the innovation of the multi-sensor integrated navigation system into the optimal ROI size of the traffic lights online. Finally, we use the YOLOv4 model to detect and recognize the traffic lights in the ROI. Based on laboratory simulation and real road tests, we verify the performance of the DEA model. The experimental results show that the proposed algorithm is more suitable for the application of autonomous vehicles in complex urban road scenarios than the existing achievements.

Robust Outdoor Positioning Via Ray Tracing

Positioning problem can be solved with several approaches in 5G. This paper introduces RT (Ray Tracing) technique for small-cell Outdoor positioning and tracking for systems with distributed architecture with multipath processing gain. Proposed approach exploits high-resolution angular spectrum estimation and known radio propagation environment. It solves positioning problem robustly even in NLOS cases via CoMP (Cooperative Multi Point) reception and joint processing at cloud CPU. The aim of this paper is to disclose proposed algorithm for NR and compare it to GNSS measurements.

A Comprehensive Review of GNSS/INS Integration Techniques for Land and Air Vehicle Applications

Navigation systems are of interest for applications in both civilian and military vehicles. Satellite navigation systems and inertial navigation systems are the most applied in this area. They have complementary properties, which has led to a trend of integrating these systems. At present, there are several approaches to GNSS/INS integration: loosely coupled, tightly coupled and deeply coupled and many approaches to their modifications in dependence of application and arising problems with measurements, such as lack of GNSS measurements or poor quality of GNSS and INS measurements. This article presents an extensive review of the available modern approaches and their modifications for integrating INS and GNSS measurements, arranging them and highlights the main problems arising for the considered type of integration approach. The article includes a review of various integration tools based on the Kalman filter and intelligent systems, INS mechanization and features of development of an INS measurement error model that is necessary for integration, the main problems of GNSS/INS integration and a comparative description of the solutions proposed by the authors for solving these problems. The findings of this work are useful for further research in the field of inertial and satellite navigation, as well as for engineers involved in the practical implementation of integrated GNSS/INS systems.

High-precision velocity determination using mass-market Android GNSS measurements in the case of anomalous clock variations

High-precision velocity determination using mass-market Android GNSS measurements in the case of anomalous clock variations

Визначення еталонних напрямків на сертифікованому поліґоні з використанням GNSS вимірювань

This work examines the results of experimental GNSS measurements in 2022 performed at the points of the scientific geodetic range (NSG). The purpose of the research is to perform simultaneous GNSS measurements at four points of the reference linear base (ELB) section and to process experimental GNSS observations at points of the metrological calibrated geodetic network to determine reference azimuths and directional angles. Method. Experimental measurements were carried out using two frequency GNSS receivers with every second registration of signals and binding to the nearest permanent stations that are part of the International GNSS service: GEOTERRACE. The paper considers the application of the method of calculating azimuths using geodetic coordinates of points and parameters of reference ellipsoids. The results. Data processing of synchronous observations of points (ELB) and permanent stations was performed in the Leica Geo Office software complex. The value of the marginal error of determining the coordinates of the investigated points does not exceed 5 mm. The results of the calculations of the investigated azimuths for different coordinate systems and the accuracy of their determination are given. The parameters of the Krasovsky, WGS-84 and ITRF 2000 ellipsoid references were used for the calculations. The calculated values of the direction angles in the USK 2000 coordinate system for the six-degree zone. Scientific novelty. The possibility of using GNSS measurements for creating reference directions, determining their azimuths and directional angles is shown. An accuracy assessment was carried out based on the results of the measurements. The calculated accuracy of determining the azimuths of the directions depends on the accuracy of determining their coordinates and the distance between observation points. The obtained formula for calculating the accuracy of direction determination in angular units. Practical significance. The stability of the points calibrated by the metrological service of the ELB NHP section over time has been confirmed, which gives grounds for using the investigated directions as standards for calibration of navigation equipment. Calculated azimuths and direction angles of the selected directions for different coordinate reference systems. The calculated value of the convergence of the meridians for the six-degree zone of USK 2000 point P-1. The obtained values of true azimuths can be used to study the inclination of the magnetic needle.

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.

The 26 November 2019 Durrës earthquake, Albania: coseismic displacements and occurrence of slow slip events in the year following the earthquake

SUMMARYOuter Albanides experienced a seismic sequence starting on 21 September 2019, with an Mw 5.6 earthquake, considered a foreshock, and culminated with the main shock on 26 November 2019, followed by a paramount aftershock activity. We propose a model for the coseismic slip distribution using InSAR, permanent, and campaign GNSS measurements. We tested two hypotheses: an earthquake on a thrust plane with the direction N160° and along with a back thrust. By varying the depth and dip angle for the first hypothesis and only the dip angle for the second hypothesis, we concluded the optimal solution is a blind thrust at a 15-km depth dipping eastward 40°, a maximum slip of 1.4 m and an Mw 6.38. A GNSS time-series obtained after 2020 shows two slow slip events (SSEs): the first one is 200 d after the main shock up to 26 d, and the second one is 300 d after the main shock up to 28 d. We tested three hypotheses: SSE along the basement thrust where the main shock has been localized, SSE along the flat formed by the detachment layer of the cover, and SSE along these two faults. We concluded that SSE occurred along the detachment layer or along the two faults.

Barometer assisted smartphone localization for vehicle navigation in multilayer road networks

Multilayer transport structures, such as elevated roads and tunnels, are increasingly used to solve the growing traffic congestion problems in dense urban areas. It presents a challenge for navigation systems to determine which layer the vehicle is running on when elevated roads or tunnels are parallel to and close to surface roads. In this paper, we propose a smartphone-based positioning method to provide accurate position and road layer for vehicle navigation in multilayer road networks. Systemic errors of barometers are calibrated with GNSS measurements, local Digital Surface Model (DSM), and Mean Sea Level pressure. Then, barometer output absolute altitudes are integrated with GNSS and IMU to achieve 3D vehicle positioning. Using absolute altitudes, DSM, and GNSS information, the road layer can be identified without initial layer information in multilayer road networks. Experiment results demonstrate that the proposed method can provide accurate location and road layer in multilayer road networks.

Assessments of recent Global Geopotential Models based on GPS/levelling and gravity data along coastal zones of Egypt

Abstract The orthometric height has an essential role in a variety of civil engineering projects and it is defined as the length of the curved plumbline from a point (on the earth surface) to its intersection with the geoid surface. Leveling process is considered as the most accurate technique for obtaining these heights. However, regardless of its potentials, it is tedious, costly, and time consuming. Recently many organizations and research centers have developed multi Global Geopotential Models (GGMs) depending on several types of available gravity and height datasets to estimate orthometric heights from GNSS measurements. In this study, we present an evaluation and assessment of the accuracy of five of recent and popular GGMS: XGM2016, XGM2019e, EIGEN-6C4, GO_CONS_GCF_2_TIM_R6e, and EGM2008 using actual 145 GNSS/leveling points and 96 terrestrial gravity points. The goal of this research is to find the best fit model along the study area located along the coastal zones of Egypt with distances of about 1,970 km for further determination of geoid modeling at regional scale. The selection of these areas basically was due to their developmental, urban, and economical importance and their continuous need for protection works to fight against the coastal erosion caused by climate change and global warming. The results indicated that for geoid undulation, GO_CONS_GCF_2_TIM_R6e model is the best fit GGM for the estimation of geoid model along Mediterranean Sea coastal line, while XGM2019e_2159 model is the best suitable for coastal line of the Red Sea. And regarding the gravity anomalies, the most reliable GGMs for this study area are XGM2019e_2159 and EIGEN-6C4 for Bouguer and free-air gravity anomaly, respectively.

Validation of Recent DSM/DEM/DBMs in Test Areas in Greece Using Spirit Leveling, GNSS, Gravity and Echo Sounding Measurements

Recent Digital Surface, Elevation, and Bathymetric Models (DSM/DEM/DBM) aim to provide high-resolution and accurate height and depth information needed for a variety of surveying, geodetic, geophysical, and other applications. In this study, first we aim to validate in two test areas some of the most used models, i.e., ASTER GDEM; AW3D30 DSM; Copernicus DEM; EU-DEM; GEBCO 2020; NASADEM HGT; SRTM15+ and SRTM Global, using GNSS; spirit leveling; and gravity measurements. The validation is performed along two traverses of 14.5 and 12.0 km each in Northern and Central Greece, respectively. Since these models are based on geoid heights obtained from global geopotential models, we also investigate their influence on the validation results. Next, we carry out comparisons between GEBCO 2020, SRTM15+, and the Greek Seas DTM, with depths derived from in situ coastal measurements in six different areas in Northern Greece. From the analysis, we conclude that the heights obtained from the Copernicus DEM provide the best overall results in terms of mean value and standard deviation while also showing consistent results in the two test areas. Similarly, the Greek Seas DTM shows better consistency with the measured depths in the coastal test areas.

The prospects of integrated use of high-precision geometric and GNSS leveling for studying neotectonic processes at geodynamic polygons

This article presents the development of a methodology for determining the deviation of straight lines using high-precision leveling and GNSS measurements, its estimated accuracy, and the justification of technological parameters for constructing geodynamic testing grounds. This problem is essential in the geodetic and geophysical fields since changes in the shape of the equipotential surface may indicate a redistribution of mass in the Earth's crust and other natural phenomena. Studying this problem using the proposed methodology can provide insight into the main geological processes, gravitational potentials, and neotectonic processes. Monitoring of changes and deformation of the Earth's surface is of great importance for understanding solid processes on the Earth, especially those caused or intensified by anthropogenic activities, which currently pose global challenges to humanity. The study presents the analysis of the existing methods for determining the change in the shape of the equipotential surface. It substantiates the advantages of using high-precision leveling and GNSS measurements to ensure the accuracy and reliability of the results. The calculation formulas for estimating the accuracy of determining the deviation of straight lines with the possibility of studying the shape of equipotential surfaces with millimeter accuracy are proposed. The methodology and technological parameters have been developed, which can be used to determine the change in the deviation of a straight line on geodynamic polygons with an accuracy of 0.1-0.2". Also, the possibility of using the research results to determine changes in the shape of equipotential surfaces is theoretically substantiated. Namely, changes in their radii of curvature are associated with the possibility of predicting neotectonic processes according to modern scientific hypotheses. Keywords: deviation of straight lines; global navigation satellite systems; geometric leveling; orthometric excesses; geoid, geodetic heights.