GNSS Data Research Articles

A New Algorithm for Measuring Vegetation Growth Using GNSS Interferometric Reflectometry

The use of global navigation satellite system interferometric reflectometry (GNSS-IR) to measure vegetation growth status has become a rapidly growing technique in remote sensing. GNSS signals reflected by the soil surface affect the accuracy of vegetation growth status (vegetation cover density) measurement, and the influence of soil moisture (SM) varies. This study establishes a calibration model that can reduce the influence of SM and snow layer on reflectivity. We used a direct-reflected signal amplitude ratio and GNSS-IR altimeter based on the Lomb–Scargle Periodogram to calculate the reflectivity of vegetation and snow layer depth. GNSS data from plate boundary observation were used to verify the validity of our model. The results show that reflectivity correlates better with vegetation growth status after calibrating the influence of the SM and snow layer. Moreover, the correlation increased by nearly 0.14. This study analyzed the influence of the snow layer and found that it had a noticeable effect on vegetation growth status measurement when the snow depth was over 30 cm. Furthermore, a fusion method is proposed to improve the accuracy of vegetation growth status measurement by combining the reflectivity and normalized microwave reflection index (NMRI). The experimental results show that better performance can be obtained compared to the single observation of the reflectivity and NMRI, and the best correlation between the measured and in situ normalized difference vegetation index is over 0.91, and the root mean square error decreases to 0.1893.

A Methodology for Combine Performance Analyses in Wheat Harvests with GNSS Data

Highlights Proposed a novel methodology for fully automated, low-cost, and high-resolution harvest performance analyses. Described methods for estimating key features, such as the center of the header, using noisy positioning data. Introduced metrics Swath Utilization and Spatial Field Capacity to evaluate temporal and spatial performances. Provided case studies of using these two new metrics to compare combine performances by machines and by years. Abstract. Combine harvesters’ performance during wheat harvests can be analyzed using various methods. These methods typically rely on traditional field-level metrics, such as those defined by ASABE, to address average performances in terms of field or machine. However, next-generation digital agriculture technologies have significantly increased the operation precision of agricultural activities. As a result, the evaluation of instantaneous performance becomes possible. This work introduces a novel methodology that enables fully automated, low-cost, and high-resolution (both in time and space) instantaneous combine performance analyses based on global navigation satellite system (GNSS) positioning records. The methodology incorporates a multi-step, easy-to-follow workflow with customizable modules for efficient and effective data processing. This way, the computation of traditional field capacity metrics can be fully automated even if multiple combines cooperate in harvesting the same field. Furthermore, two groups of novel metrics are proposed: Swath Utilization and Spatial Field Capacity. They enhance traditional metrics by analyzing machine performances both temporally and spatially on a finer scale. As a case study, we computed these metrics for seven fields in Colorado, USA, during wheat harvests across five different years. We compared the results with typical values from ASABE standards to validate the correctness of our data processing methodology. We also provided four analysis examples with a rich set of temporal and spatial visualizations to showcase how our metrics can accurately assess combine performances, quantitatively uncover harvest details, and effectively compare operations in different fields/years for better practice. These new analyses enabled by our methodology are required to harness the full potential of digital agriculture. Keywords: Combine harvester, Field capacity, Global navigation satellite system (GNSS), Kalman filter, Optimization, Positioning data, Wheat harvest performance.

Improving Detection of Unsteady Crustal Deformation by using GNSS Data: Common Mode Error Reduction, Target Area Expansion to Hyuga-Nada, and Transient Signal Monitoring with Postseismic Deformation Removal

Improving Detection of Unsteady Crustal Deformation by using GNSS Data: Common Mode Error Reduction, Target Area Expansion to Hyuga-Nada, and Transient Signal Monitoring with Postseismic Deformation Removal

An Improved Method for Water Body Removal in Spaceborne GNSS-R Soil Moisture Retrieval

The global soil moisture (SM) retrievals by the spaceborne Global Navigation Satellite System-Reflectometry (GNSS-R) are significantly influenced by the presence of water bodies. The traditional method is to build a grid based on the location of satellite sampling points and determine the presence or absence of water bodies. In this paper, we propose a water body removal method for global spaceborne GNSS-R SM retrievals that combines water bodies and buffers derived from the marginal areas around water bodies as mask data, thus achieving accurate removal of the water body and avoiding margin effects. To verify the effectiveness of the proposed method, the Cyclone GNSS (CYGNSS) data with two different spatial resolutions (36 km and 3 km) were used for SM retrieval, and the Soil Moisture Active and Passive (SMAP) Radiometer SM as well as the International Soil Moisture Network (ISMN) were used as references. Results show that the correlation coefficient (R) and root mean square error (RMSE) of the 36 km grid are 0.50 and 0.057 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , respectively, while the R and RMSE of the 3 km grid are 0.68 and 0.041 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , respectively. Such performances are better than the traditional method. Moreover, the method proposed in this paper preserves more grids. Take the 3 km spatial resolution for example, it preserves 2.2 fold grids more than the traditional water body removal method. In the comparison with SMAP SM, the overall improvement of RMSE by using the water body removal method proposed in this paper is 16.3% (8.2% for the traditional method). In the in-situ validation, the overall improvement of RMSE is 19.4% (-1.2% for the traditional method). Therefore, in the future high spatial resolution SM retrieval, the water body removal method proposed in this paper can preserve the maximum area and effectively eliminate the influence of water bodies on SM retrieval.

Toward the Future Generation of Railway Localization Exploiting RTK and GNSS

Smart sensors have become pervasive in railway transportation applications, particularly in Europe where digital technologies are increasingly being applied to the railway signalling field. In the future, safety-critical track-side train detection equipment, such as track circuits and axle counters, will be eliminated in favor of an accurate position estimate supplied by the train. However, the best approach to calculate an accurate position estimate remains an open research question, especially due to the high availability and reliability required. This paper describes two static experiments performed with a GNSS module, which demonstrate that the real-world accuracy achievable with GNSS and Real Time Kinematic (RTK) alone is not sufficient for safety-critical applications, meaning further complementary sensors are required. Furthermore, a custom sensor node containing a GNSS module with RTK and an Inertial Measurement Unit (IMU) has been used to acquire several data sets from an operating passenger train during dynamic tests on a railway line between Formigine and Modena, in Emilia-Romagna, Italy. These labeled GNSS and IMU data have been made freely available to the scientific community. The positioning accuracy of the GNSS and RTK measurements is evaluated, providing an in-depth study of the localization error and satellite coverage on the entire route. We demonstrate, with experimental evaluation, that centimeter accuracy (1.9 ± 0.8 cm) is achievable under favorable static conditions, while accuracy can deteriorate to 8m with RTK in urban scenarios with many reflections and poor sky view, worse than with GNSS alone. Under controlled conditions we show that shielding the GNSS receiver without RTK with a grounded metal plate causes a reduction in accuracy from 0.80 ± 0.04m to 3.70 ± 0.55m in the least and most shielded case respectively. Our dynamic tests on a train show that although at least meter-level accuracy (1.08 ± 1.30 m) is achievable with GNSS and RTK alone under dynamic conditions, a sensor fusion approach is necessary to accurately localize trains when GNSS conditions are poor or GNSS is unavailable.

Single-Pass Tropical Cyclone Detector and Scene-Classified Wind Speed Retrieval Model for Spaceborne GNSS Reflectometry

Spaceborne global navigation satellite system reflectometry has been used to retrieve wind speed, but few studies have directly detected tropical cyclones from spaceborne GNSS-R observations. Moreover, it is challenging to solve the multivalued dependence of the spaceborne observable on wind speed to unambiguously and accurately retrieve wind speed in cyclone conditions. This paper presents a single-pass cyclone detector and coarse estimation approach of the tropical cyclone position using a spaceborne GNSS-R full delay-Doppler map (FDDM). When the specular point passes through a tropical cyclone, the FDDM asymmetry experiences an abnormal change. From the FDDM asymmetry sequence along the specular point trajectory, two subsequence features, including the slope and extremum difference, are defined, from which the tropical cyclone detector is proposed. The results from the simulation and the Cyclone GNSS (CYGNSS) data both indicate a good detection performance for tropical cyclones. The location corresponding to the peak detector is considered as a coarse estimation of the tropical cyclone position. The test result from the CYGNSS data shows that the mean error between the detected cyclone center and the International Best Track Archive for Climate Stewardship (IBTrACS) cyclone center is approximately 124.50 km. From the detector of tropical cyclones, a scene-classified wind speed retrieval model is proposed. The simulated and experimental results show that a better retrieval performance can be obtained at high wind speed (> 30 m/s) using the scene-classified model. Reductions of 10 m/s and 4 m/s in the root mean square errors (RMSEs) are obtained for the simulation and CYGNSS data, respectively. This work is meaningful for directly detecting tropical cyclones and retrieving high wind speed data using spaceborne GNSS-R in real time.

Processing of GNSS data in Gamit/Globk: On the example of the reference stations of the Uzbekistan network

The article presents the results of processing, a preliminary assessment of the quality of measurements, and the accuracy of the coordinates of the points of the reference network of Uzbekistan (MAGK, FARG, JARQ, and URGA). Observation data of GNSS points were processed using the GAMIT/GLOBK v.10.71 software package by applying standard procedures for position and velocities estimation relating to the ITRF2014 global reference frame. The horizontal velocities of points were compared with the latest versions of global tectonic models such as ITRF 2014, GEODVEL 2010, and NNR - MORVEL 56. Analysis of the point time series confirmed the good quality of the measurements and the accuracy of the processed coordinates in the GAMIT/GLOBK program. The calculated solutions had horizontal coordinates, uncertainties uncertainty, and repeatability, at the level of 1-3.2 mm for horizontal coordinates and 3.2-6.5 mm for height. However, the analysis of the horizontal velocities of points and comparison of the results with global tectonic models confirmed the need for further compaction of the regional satellite network, especially in the western part of the territory, taking into account the new model of modern movements of the region.

Analysis of GNSS data quality based on Anubis and RTKLIB and single-point positioning accuracy in different environments for Android smartphones

Analysis of GNSS data quality based on Anubis and RTKLIB and single-point positioning accuracy in different environments for Android smartphones

An Estimation of Precipitable Water Vapour Around Surabaya City Using GIPSY-X

Precipitable water vapor is a crucial climatic parameter that indicates the available humidity in the atmosphere. Precipitable water vapor is produced by evaporation/evapotranspiration from the surface to the atmosphere and thus plays an important role in the water cycle. As an essential indicator of climate change, water vapor contributes significantly to the thermodynamics of the atmosphere. Zenith Total Delay can be calculated using the Precise Point Positioning strategy and all parameters. Using the parameter mapping function, Slant Tropospheric Delay can be converted to Zenith Total Delay, which is affected by temperature, pressure, and humidity. We processed the GNSS data from five stations surrounding Surabaya City using GipyX. Advanced processing generates five minutes of ZTD estimation on each station for five years of observation. A high correlation of ZTD estimated using GipsyX (corr = 0.88) with ZTD at meteorological rinex data of DARW station shows our estimation’s promising and dependable result. The ZTD time series shows consistent patterns on each station, showing the significant contribution of regional signals such as monsoon and ENSO.

ПЕРСПЕКТИВИ ОЦІНЮВАННЯ ТРИВИМІРНИХ ДЕФОРМАЦІЙ ЗЕМЛІ ЗА ДАНИМИ ГЛОБАЛЬНИХ НАВІГАЦІЙНИХ СУПУТНИКОВИХ СИСТЕМ

Presented in the article information is of a scientific and methodical character. Accumulation of coordinate monitoring data in networks of permanent GNSS stations made it possible to increase the efficiency of solving of many problems of moderngeodynamics. At the same time, their use made it necessary to rethink traditional theoretical approaches to solving of the problem, in particular, in terms of developing methods for evaluation of three-dimensional deformations.The analysis of the used theoretical approaches and methods for evaluation of three-dimensional deformations of the Earth in this article are presented. The insufficient degree of their correspondence to the potential information resource of GNSS data is substantiated.The method for evaluation of deformations of the Earth from the standpoint of the theory of transformations of Riemannian space imagesin the form of complex diffeomorphic manifolds is proposed. Properties of complex manifolds in the form of a tangent Euclidean space, which is parameterized by a rectangular Cartesian coordinate system, are used. This choice is justi-fied by its identity with the ITRS system, which is used to monitoring of coordinates by the GNSS method. The algorithm for constructing a functional model of deformation based on the homeomorphism of transformations is formulated. The method involves the direct use of coordinates in the ITRS system and modeling of deformations of the curvilinear topographic surfaceof the Earth in three-dimensional space. The method provides evaluation of three-dimensional deformation tensors and related invariants, which belong to the topographic surface. Working formulas for evaluation of main linear deformations, dilatation and rigid rotation of the Earth have been obtained. The method is generalized for evaluation of nonlinear deformations

Local Geoid height calculations with GNSS, airborne, and spaceborne Lidar data

Determining the exact position of objects on the Earth’s surface is extremely important. The general purpose of this study is to calculate local geoid and orthometric heights of points obtained from ICESat-2/ATLAS, airborne LIDAR, and GNSS/CORS data and to investigate the performance of ICESat-2/ATLAS in predicting ground heights in urban areas. The calculated geoid and orthometric height values from ICESat-2/ATLAS were compared with the height values from the airborne LIDAR and GNSS/CORS data. In this study, a total of 52 points were collected in the field using the GNSS/CORS system. The accuracy of the geoid heights of these points was verified using three different methods: (a) using 12 local C1-C3 degree GPS leveling points, (b) using the new Turkey Geoid 2020 (TG20), and (c) using the improved TG20 dataset by applying interpolation methods. In addition, interpolation methods including weighted arithmetic mean, kriging, multi-quadratic, polynomial, and TIN were applied to our datasets. Statistical analyses including RMSE, MSE, MAE, ME, and R2 were applied to our datasets. As a result, the accuracy values based on polynomial interpolation method between LIDAR-ICESat-2/ATLAS were found to be as RMSE = 2.003 cm, MSE = 4.013 cm, MAE = 1.748 cm, ME = 0.004 cm, and R2 = 1.00. The accuracy values between GNSS/CORS-ICESat-2/ATLAS were found to be as RMSE = 3.091 cm, MSE = 9.558 cm, MAE = 2.723 cm, ME = 1.401 cm, and R2 = 1.00,. According to our results, the relationship between LIDAR-ICESat-2/ATLAS is better than the relationship between GNSS/CORS-ICESat-2/ATLAS.

Application of Machine Learning to GNSS Data Collected by Smartphone

Trends showing increase in the number of mobile device users, as well as the number of tourists, imply that more people rely on their smartphones when navigating in a new environment. Based on these facts, the idea for this experimental research appeared. That idea is applying the process of machine learning, more precisely, the implementation of a neural network, to investigate the possibility of improving the accuracy of smartphone navigation. The achieved results indicate that machine learning algorithms (neural networks) are a powerful tool that can also be applied to GNSS data collected by a smartphone device, in order to improve accuracy. Based on the collected data in the field, preprocessing and machine learning process, it is concluded that it is possible to improve the accuracy of mobile device navigation by up to 50%.

Modeling of temporal and spatial changes of mountain bike use with voluntary geographical data: the case of the Datça Peninsula

Dağ bisikleti, popüler bir rekreasyon ve turizm aktivitesidir. Rekreasyonel ve korunan alanların sürdürülebilir yönetiminde dağ bisikleti kullanımının zamansal ve mekânsal verilerine ihtiyaç duyulmaktadır. Geleneksel veri toplama yöntemleri pahalı, zaman alıcı ve zamansal-mekânsal ayrıntılardan yoksundur. Günümüzde GNSS tabanlı mobil uygulamalardan elde edilen gönüllü coğrafi veriler, dağ bisikleti kullanımının zamansal ve mekânsal analizi için önemli bir veri kaynağı haline gelmiştir. Bu çalışmada gönüllü coğrafi veri perspektifine dayalı olarak, GNSS verileri aracılığıyla Datça Yarımadası’nda dağ bisikleti kullanımının zamansal ve mekânsal değişimlerinin modellenmesi amaçlanmıştır. Wikiloc platformunda paylaşılan 203 adet seyahat rotasının GNSS izleri kullanılarak oluşturulan grafikler ve yoğunluk haritaları ile dağ bisikleti kullanımı analiz edilmiştir. Çalışmanın sonuçları, kitle kaynaklı Wikiloc verilerinin, dağ bisikleti kullanımının zamansal ve mekânsal özelliklerini analiz etmek için veri kaynağı olarak kullanılabileceğini göstermiştir. Çalışma, gönüllü coğrafi verilerin avantajlarından yararlanarak rekreasyonel ve korunan alanların sürdürülebilir yönetimi için gelecekteki araştırmaların önünü açmaktadır.

Assessment of the accuracy of low-cost multi-GNSS receivers in monitoring dynamic response of structures

The monitoring of bridges is a crucial operation for their structural health examination and maintenance. GNSS technology is one of the methods which are applied with the main advantage that the direct measurement of the bridge displacement is conducted in an independent global coordinate system. However, the high cost of the GNSS stations, which are consisted of dual-frequency receivers and geodetic GNSS antennas, is the main reason of the limited application of GNSS for bridge monitoring. In this study, we assessed the performance of low-cost multi-GNSS receivers in monitoring dynamic motion, similar to that of bridge response. The performance of the low-cost GNSS receivers was assessed based on controlled experiments of horizontal and vertical motion. For the horizontal motion, controlled experiments of circular motion of various predefined radius between 5 and 50 cm were executed where the low-cost GNSS receivers were assessed against dual-frequency geodetic receivers. For the vertical motion, manually controlled experiments of vertical oscillations of amplitude 8 and 15 mm were executed where the low-cost GNSS receivers were assessed against the Robotic Total Station (RTS). Finally, a low-cost monitoring system formed by two closely spaced low-cost GNSS receivers was applied in dynamic displacement monitoring of the Wilford Suspension Bridge. The analysis of the low-cost GNSS data revealed the beneficial contribution of (i) the multi-constellation on the accuracy and precision of the GNSS solution and (ii) the combination of closely spaced low-cost GNSS receivers, to limit potential cycle slips and the low-cost GNSS noise level and reach accuracy and precision similar to that of geodetic-grade GNSS receivers. This was confirmed in the bridge monitoring application, where the main modal frequency and the response amplitude of the bridge were identified successfully by the low-cost GNSS receivers’ data analysis.

Modelling Productivity in Extraction Operations by Simulations Based on GNSS Documented Data: An Example from Skidding Teak Wood In Thailand

In Thailand, teak harvesting always includes skidding of tree-length stems from the landing to the log yard for further processing. When terrain does not set limitations for the machines to be used, skidding is carried out by farm tractors. In this study, data was collected from 10 work cycles of teak extraction to simulate the productivity of farm tractors. The GNSS data as speed and locations were used to extract operational distances and time consumption, as well as to support productivity simulation. For this, detailed measurements were done on the extracted stems to collect their diameters and lengths. For approximately six stems per load, the mean load size was 1.723 m3. The study found that mean productivity was 17.4 m3/h during the survey, where the mean extraction distance was 217 m. Our simulation presents productivity diagrams in relation to skidding distance. By simulation, we detected that reducing the full operational speed by 1 km/h would decrease productivity by 1 m3/h when the extraction distance is less than 100 m. Another observation was that even small reductions in load sizes have a remarkable effect on productivity over short distances. Until large-scale studies are to be done to evaluate productivity in relation to variations in load size and extraction distance, the results shown herein could stand as a basis for productivity assessments.

Effects of Tropospheric Refraction on Precise Point Positioning in Brazil

Troposphere is one of the most limiting sources of error in the accuracy of 15 Precise Point Positioning method. This work aims to analyze the effects of tropospheric 16 delay on this positioning technique by applying the Bernese scientific program to GNSS 17 data belonging to the Brazilian Network for Continuous Monitoring of GNSS Systems. 18 GNSS data are related to several climatic zones, including Amazon region, referring to four 19 seasons. The data were processed considering six strategies, each one using different 20 troposphere models and mapping functions for analysis. Results were evaluated according 21 to the Root Mean Square, estimated for 15 processing days for each season, involving 89 22 GNSS stations. Results show that the greatest effects of the tropospheric delay occurred in 23 the equatorial region, related to the altimetric component, in all seasons of the year. This 24 climatic zone is under a strong influence of the Amazon region, which presents high annual 25 humidity values. In addition, it can occur a great humidity variation in this region, which 26 can compromise the process of estimating wet component of tropospheric delay. Finally, 27 results showed that the best processing strategy was the use of the Vienna mapping function 28 in conjunction with corrections based on the Numerical Weather Forecast model.

GNSS Data Processing and Validation of the Altimeter Zenith Wet Delay around the Wanshan Calibration Site

The Wanshan calibration site (WSCS) is the first in-situ field for calibration and validation (Cal/Val) of HY-2 satellite series in China. It was built in December, 2018 and began business operation in 2020. In order to define an accurate datum for Cal/Val of altimeters, the permanent GNSS station (PGS) data of the WSCS observed on Zhiwan (ZWAN) and Wailingding (WLDD) islands were processed using GAMIT/GLOBK software in a regional solution, combined with 61 GNSS stations distributed nearby, collected from the GNSS Research Center, Wuhan University (GRC). The Hector software was used to analyze the trend of North (N), East (E), and Up (U) directions using six different noise models with criteria of maximum likelihood estimation (MLE), Akaike Information Criteria (AIC), and the Bayesian Information Criteria (BIC). We found that the favorite noise models were white noise plus generalized Gauss–Markov noise (WN + GGM), followed by generalized Gauss–Markov noise (GGM). Then, we compared the PGS velocities of each direction with the Scripps Orbit and Permanent Array Center (SOPAC) output parameters and found that there was good agreement between them. The PGSs in the WSCS had velocities in the N, E, and U directions of −10.20 ± 0.39 mm/year, 31.09 ± 0.36 mm/year, and −2.24 ± 0.66 mm/year for WLDD, and −10.85 ± 0.38 mm/year, 30.67 ± 0.30 mm/year, and −3.81 ± 0.66 mm/year for ZWAN, respectively. The accurate datum was defined for Cal/Val of altimeters for WSCS as a professional in-situ site. Moreover, the zenith wet delay (ZWD) of the coastal PGSs in the regional and sub-regional solutions was calculated and used to validate the microwave radiometers (MWRs) of Jason-3, Haiyang-2B (HY-2B), and Haiyang-2C (HY-2C). A sub-regional PGS solution was processed using 19 continuous operational reference stations (CORS) of Hong Kong Geodetic Survey Services to derive the ZWD and validate the MWRs of the altimeters. The ZWD of the PGSs were compared with the radiosonde-derived data in the regional and sub-regional solutions. The difference between them was −7.72~2.79 mm with an RMS of 14.53~18.62 mm, which showed good consistency between the two. Then, the PGSs’ ZWD was used to validate the MWRs. To reduce the land contamination of the MWR, we determined validation distances of 6~30 km, 16~28 km, and 18~30 km for Jason-3, HY-2B, and HY-2C, respectively. The ZWD differences between PGSs and the Jason-3, HY-2B, and HY-2C altimeters were −2.30 ± 16.13 mm, 9.22 ± 22.73 mm, and −3.02 ± 22.07 mm, respectively.

A Deeper Look Into the 2021 Tyrnavos Earthquake Sequence (TES) Reveals Coseismic Breaching of an Unrecognized Large‐Scale Fault Relay Zone in Continental Greece

AbstractLarge magnitude (Mw ∼ ≥6) earthquakes in extensional settings are often associated with simultaneous rupture of multiple normal faults as a result of static and/or dynamic stress transfer. Here, we report details of the coseismic breaching of a previously unrecognized large‐scale fault relay zone in central Greece, through three successive normal fault earthquakes of moderate magnitude (Mw 5.7–6.3) that occurred over a period of ∼10 days in March 2021. Specifically, joint analysis of InSAR, GNSS and seismological data, coupled with detailed field and digital fault mapping, reveals that the Tyrnavos Earthquake Sequence (TES) was accommodated at the northern end of a ∼100 km wide transfer structure, by faults largely unbroken during the Holocene. By contrast, the southern section of this relay zone appears to have accrued significant slip during Holocene. InSAR‐derived displacements agree with the loci of eight subtle, previously undetected, faults that accommodated coseismic and/or syn‐seismic normal fault slip during the TES. Kinematic modeling coupled with fault mapping suggests that all involved faults are interconnected at depth, with their conjugate fault‐intersections acting largely as barriers to coseismic rupture propagation. We also find that the TES mainshocks were characterized by unusually high (&gt;6 MPa) stress‐drop values that scale inversely with rupture length and earthquake magnitude. These findings, collectively suggest that the TES propagated north‐westward to rupture increasingly stronger asperities at fault intersections, transferring slip between the tips of a well‐established, but previously unrecognized, relay structure. Fault relay zones may be prone to high stress‐drop earthquakes and associated elevated seismic hazard.

Improved height correction model for hydrostatic mapping functions in GNSS data processing

Improved height correction model for hydrostatic mapping functions in GNSS data processing

Long-term monitoring of recent crustal movements in the region of Southwestern Bulgaria. Results from 2022

This article examines the study of modern crustal movements in the region of southwestern Bulgaria, a geologically and seismically active region with the presence of numerous fault structures. The main method of obtaining deformation information is by using GNSS measurements. The monitoring of geodynamic processes in the area has been going on for more than 25 years. GNSS data obtained from periodic campaign measurements between 1997 and 2022 are processed and analyzed to obtain the deformation accumulation result in southwestern Bulgaria. As a result of long-term measurements, more and more accurate and reliable results are obtained for the velocities of the points. A certain relationship has been established between the modern movements of the Earth’s crust, seismic events and tectonic structures. This extensive movement of southern Bulgaria and northern Greece is also confirmed. The results can be used for a detailed geodynamic and geological study of the active fault structures in the area.