Search

Employing high precise positioning ability, the global navigation satellite systems (GNSS) could accurately capture subtle deformations in bridges, supplying critical data for structural health monitoring. However, GNSS antennas placed on bridges often encounter multipath interference generated by bridge deck and water surface reflections, compromising the quality of observation data and positioning accuracy. Through the analysis of GNSS data collected from an operational bridge and an oceanic construction platform, we discovered a strong correlation between pseudorange multipath and carrier multipath components. Subsequently, through a series of steps including phase adjustment, decorrelation, and resolution, we successfully mitigated the multipath within residuals, and then reconstructed the corrected residuals into displacements; in addition, the method does not require advance deployment of GNSS equipment to collect calibration information. In terms of positioning results, the proposed method improves the accuracy by 27.1–32.1% in the WLMS (Weighted Least-Mean-Square) resolution and by18.8–32.9% in KF (Kalman Filter) resolution, effectively weakening the multipath interference in carrier phase observations and significantly improving positioning accuracy. [ABSTRACT FROM AUTHOR]

Global Navigation Satellite System fast precise positioning can be achieved with accurate ionospheric corrections computed from an adequate number of GNSS stations in a local region. In low-latitude regions, the presence of electron density gradients over short distances can lead to outliers in the map of ionospheric corrections and decrease its accuracy. In this study, we explored outlier detection in ionospheric correction mapping through statistical residuals during a four-month test in 2021. Our findings indicate that the residuals of the local ionospheric model conform to the Laplace distribution. To determine outliers, we use an empirical rule for the Laplace distribution, setting thresholds at μ ± 3b, μ ± 3.5b, and μ ± 5.8b for data retention rates of 95%, 97%, and 99.7%, respectively. Here, μ represents the location parameter, which corresponds to the median of data, and b is the scale parameter, calculated as the medium absolute deviation. We found that while removing outliers can improve model accuracy, it may result in unavailable prediction due to a lack of data in a spare network. For example, applying a μ ± 3.5b threshold for outlier removal led to approximately 2.5% of recording time having no ionospheric corrections map in low-latitude regions, however, the local model has the potential to improve its mean accuracy by up to 50% for both low and mid-latitudes. Therefore, choosing the appropriate percentile threshold depends on the network configuration and the desired accuracy. Removing erroneous satellite data to improve ionospheric accuracy brings positive impacts on precise positioning. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Computer Engineering & Applications is the property of Beijing Journal of Computer Engineering & Applications Journal Co Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The demand and establishment of continuously operating reference stations (CORSs) are growing fast around the world including in African countries due to having several benefits, such as the provision of accurate, homogeneous positional coordinates and the reduction of duplication and unnecessary transformation. Ethiopia prepared a 10-year geodetic infrastructure development implementation plan for modernizing geodetic services via the CORS network. To fully utilize the proposed CORS network, there is a need to investigate the overall status and limitations of the geospatial experts. The objective of this study was to gauge the awareness level and readiness of the experts to use the existing and proposed CORS in Ethiopia. A mixed research method was applied. About 244 respondents from 68 geospatial industries throughout the country filled out the survey questionnaires, and descriptive statistics were used to analyze the data. The findings of the study revealed that only 16.4% of the respondents had a better understanding of the concept of CORS and were able to operate CORS data, while 83.6% of respondents lacked the knowledge required to effectively use CORS technology for their geospatial applications. Extensive training must be given for both academics and nonacademics geospatial professionals because 98.4% of the participants currently express a desire for basic short-term CORS training that teaches them the best use of CORS technology. Practical Applications: The study attempted to investigate the overall status and limitations of the geospatial professions in Ethiopia concerning CORS technology. This study is crucial for the different global navigation satellite system (GNSS)/CORS or geospatial stakeholders such as the International GNSS Service (IGS), Space and Earth Geodetic Analysis Laboratory (SEGAL), the United Nations Committee of Experts on Global Geospatial Information Management (UN-GGIM), and the UN-GGIM Subcommittee on Geodesy, Africa Geodetic Reference Frame (AFREF) project to evaluate the progress of implementation of a global geodetic reference frame (GGRF) over the globe and a unified geodetic reference frame in Africa. The findings of the study revealed that a significant portion of the geospatial professions never used CORS due to a lack of understanding of CORS, being unable to operate it, and their organization's lack of GNSS equipment. Establishing GNSS/CORS infrastructure by itself is nothing unless work has been done on providing technical skills in data handling and dissemination and precise analysis using scientific GNSS processing software in conjunction with the technology expansion. As a result, the aforementioned and other concerned nongovernmental organizations (NGOs) should work on the capacity development of the academics and nonacademics geospatial professionals whose countries show a knowledge limitation in such technology. [ABSTRACT FROM AUTHOR]

Landslides are one of the most devastating natural disasters, with most being triggered by rainfall. Efficient monitoring and effective prevention of such slope failures are of paramount importance. This study focuses on the K3278 slope of the Daqing-Guangzhou Expressway and examines the characteristics of disasters that occurred during the course of its construction and operation. A multi-parameter monitoring system for rainfall-induced landslides is established, covering environment, displacement, and force monitoring. The early warning model comprises four distinct stages: long-term warning, mid-term warning, short-term warning, and imminent failure warning, with four levels of severity: attention, caution, alert, and alarm. The monitoring system and the warning model successfully predicted three slope hazards. Combining slope monitoring data and landslide field investigation, the destructive features and spatiotemporal evolution patterns of these hazards are analyzed. Taking the landslide event that occurred on June 20th, 2022, as a case study, the accuracy, timeliness, and effectiveness of the warning are discussed, further confirming the efficiency of the multi-parameter warning model. [ABSTRACT FROM AUTHOR]

Global ionosphere maps (GIM), a grid model generated based on observations from global GNSS stations, is often used for ionospheric delay correction and total electron content (TEC) analysis, and is an important data for ionospheric modeling and code bias estimation, as well as related applications. Understanding the spatial variation characteristics of the grid TEC in GIM data can help the better use of GIM data. In this paper, the GIM data of CODE (Center for Orbit Determination in Europe) analysis center for a total of 15 years from 2008 to 2022 are used to analyze the variation of TEC of adjacent grid points and the difference of TEC of four grid points in each grid. The results show that the mean values of the grid TEC variations range from about 0.26–1.86 TECu in the longitude direction and 0.36–2.76 TECu in the latitude direction, and most of the differences in the TECs of neighboring grid points are within ± 2 TECu. In the low solar activity years, the STD of the TEC of the four grid points in most of the grids in the GIM data is less than 1.2 TECu, indicating that the TEC values of the four grid points in most of the grids in their GIMs are relatively close to each other and the differences are small, whereas the differences are larger in the high solar activity years. In other words, the TEC values of the areas covered by the GIM grids in the low solar activity years are close. The results of the study can provide some references and lessons for the interpolation and application of the TEC of the GIM grid, and the TEC modeling of the single-station area. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cycle slips are discontinuity events in a receiver's phase lock on a Global Navigation Satellite System (GNSS) signal. If cycle-slip events are not detected and repaired, the quality of positioning using carrier phase processing suffers. In this paper, we present an algorithm for flagging cycle slips during data preprocessing. This new algorithm is part of a new GNSS software that replaces a legacy software at the National Geodetic Survey (NGS). It uses the Hatch–Melbourne–Wübbena (HMW), ionosphere-free and geometry-free linear combinations to detect cycle slips. The use of the three observables in parallel helps improve sensitivity to cycle slips and overcome the challenge of detecting cycle slips of equal size and same sign on both/multiple frequencies. Different detection threshold values were evaluated in a well-controlled environment using GNSS data acquired from continuously operating reference stations (CORS) networks and artificially simulated cycle slips that were introduced into the datasets. The goal of evaluation was to determine the optimal values for cycle-slip detection parameters. In the absence of formal confidence limits, the results of the study show that, in a worst-case scenario involving small slips of magnitudes ranging from 1 to 3 cycles, there is a range of parameter values that resulted in at least 97% success rate without any false detections. Based on these and other findings, we provide a set of optimal values from which the results are an improvement of at least 34% in cycle-slip detection, compared to results from the legacy algorithm's settings. The results of the study will support the National Oceanic and Atmospheric Administration's (NOAA) GNSS services and tools for the public, such as the Online Positioning User Service (OPUS). Practical Applications: The algorithm described in this paper is part of a new GNSS software supporting the National Spatial Reference System (NSRS) modernization efforts at the US National Geodetic Survey (NGS). It replaces an existing algorithm that uses default settings for cycle-slip detection parameters. The NSRS modernization has wide implications including for GPS/GNSS tools and services such as the Online Positioning User Service (OPUS), which is widely used by surveyors, engineers, and geospatial professionals. The results in this paper show that the new algorithm's parameters provide better sensitivity to cycle slips for the type of data used in the study. The performance is based on the assumption that the GPS/GNSS data are collected using survey-grade and/or geodetic-grade receiver types such as those used in professional geodetic and land surveys, and CORS networks. Thus, the data quality is of moderate to low noise characteristics, and results show an improvement of at least 34% in the rate of cycle-slip detection. The results are based on a 30-s sampling rate, with the general knowledge that, typically, the lower the data sampling rate the harder the cycle-slip detections. (The 30-s sampling rate is the lower sampling rate compared to 15-, 5-, and 1-s sampling rates.) [ABSTRACT FROM AUTHOR]

The establishment of the Continuously Operating Reference Stations (CORS) network as a national positioning service enables high precision in surveying, mapping, and navigation applications due to developments in Global Navigation Satellite System (GNSS) technology. In this study, we determined the first CORS network locations in Ethiopia by taking into account factors such as accessibility, internet coverage, and the strength of the network geometry. We chose locations for about 228 stations for Ethiopia considering these factors. The real-time CORS network's performance was validated using a network of triangles as a reference station and a virtual reference station (VRS) within the triangles. To validate the performance of the selected networks, simultaneous GNSS observations were conducted on the reference and virtual stations. We applied Wav2 software to generate GNSS observation data on VRS locations utilizing precise coordinates of reference stations processed using Bernese 5.2 GNSS software. Both the measured and generated GNSS data on VRS were compared after processing using the same software to estimate their precise coordinates. The comparison indicated standard deviations of 0.65 and 2.7 cm in the horizontal and upward directions, respectively. Therefore, this CORS network design can be used for applications that requires a three-dimensional accuracy of less than 3 cm in the central part of Ethiopia where this validation took place. Practical Applications: The domains of surveying, infrastructure development, and geospatial engineering can all benefit greatly from this study's practical applications. For many uses, such as land surveying, environmental monitoring, and urban planning, precise and dependable geospatial data is provided via the Continuous Operating Reference Stations (CORS) network. Professionals may increase measurement accuracy, boost data gathering efficiency, and make it easier to integrate cutting-edge technologies like global positioning system and geographic information systems (GIS) by setting up a well-designed CORS network. In addition, this network may benefit many industries, such as transportation, agriculture, and disaster relief, by providing dependable positioning services that facilitate efficient resource allocation and decision-making. Additionally, the study's performance evaluation component emphasizes how critical it is to keep an eye on and optimize the operation of the CORS network. Maintaining dependable geospatial data services requires the CORS network to run at optimal efficiency as Ethiopia develops its urban areas and infrastructure. The study's conclusions can help engineers and legislators make well-informed decisions on the installation and upkeep of CORS stations, which will eventually improve public safety and location-based service accuracy. Beyond academic study, the practical consequences of this effort go beyond; they provide the groundwork for future infrastructure and technology investments that will support Ethiopia's growth and development in a constantly evolving technological landscape. [ABSTRACT FROM AUTHOR]

In 1998, the South Carolina Geological Survey (SCGS) established a state-wide coastal Surface Elevation Table (SET) network to document geodetic elevation changes (uplift or subsidence) at different spatial resolutions, quantify elevation change on salt marsh platforms over time, and compare the rate of surface elevation change (REC) at each station to the rate of local relative sea-level rise (RSLR). Analysis of short- and long-term (4 to 22 + year) datasets from 21 SCGS SET stations shows that rates vary widely, from -2.30 to + 10.17 mm/yr. The 22 + year length of record on the oldest SCGS SET datasets reveal non-linear REC trends, with short-term trends often above or below the long-term trendline. When compared to a 100-year RSLR trend of 3.36 ± 0.19 mm/year at NOAA gauge 8,665,530 (Cooper River Mouth, Charleston Harbor), 11 stations had higher rates, five were lower, and five had overlapping confidence intervals. With a shorter 23-year record, only two stations would have higher rates. All SCGS SET stations are situated high in the tidal frame. There are no discernible associations between SET positions relative to mean high water (MHW) and REC. Long-term (1998–2021) geodetic elevation data available for six of the original stations indicate some geodetic elevation loss. Data for these original stations, and nine upland benchmarks surveyed in 2022, indicate possible impacts from the underlying Garner-Edisto fault. These findings have implications for other SET programs using similar methods to quantify vertical change over decadal time spans. [ABSTRACT FROM AUTHOR]

The GNSS-based bistatic SAR (GNSS-BSAR) system has emerged as a hotspot due to its low power consumption, nice concealment, and worldwide reach. However, the weak landing power density of the GNSS signal often necessitates prolonged integration to achieve an adequate signal-to-noise ratio (SNR). In this case, the effects of the receiver's time-frequency errors and atmospheric disturbances are significant and cannot be ignored. Therefore, we propose an ionospheric scintillation compensation-based imaging scheme for dual-channel GNSS-BSAR system. This strategy first extracts the reference phase, which contains the ionospheric phase scintillation and other errors. Subsequently, the azimuth phase of the target is divided into difference phase and reference phase. We apply the two-step phase compensation to eliminate Doppler phase errors, thus achieving precise focusing of SAR images. Three sets of experiments using the GPS L5 signal as the illuminator were conducted, coherently processing a 1.5 km by 0.8 km scene about 300 s. The comparative results show that the proposed method exhibited better focusing performance, avoiding the practical challenges encountered by traditional autofocus algorithms. Additionally, ionospheric phase scintillation extracted at different times of the day suggest diurnal variations, preliminary illustrating the potential of this technology for ionospheric-related studies. [ABSTRACT FROM AUTHOR]

Multipath is recognized as one of the major error sources for GNSS urban navigation. This study proposes a random forest (RF)-based multipath parameter estimator that uses random forest regression for parameter estimation, thereby mitigating multipath effect by removing the estimated reflected signal components. The proposed estimator is evaluated and compared with the multipath estimation delay-lock loop (MEDLL) for one-multipath and three-multipath cases, respectively. Simulation results demonstrate that the RF-based estimator is less affected by the front-end bandwidth of received signals, compared with MEDLL. The proposed RF-based estimator shows better performance than MEDLL for signals with front-end bandwidths of lower than 6 MHz. In 20 sets of tests on signals with a front-end bandwidth of 10 MHz in the three-multipath case, the RF-based estimator obtains smaller standard deviations than MEDLL. In experiments using real data with a front-end bandwidth of 2 MHz, the RF-based estimator reduces the 2D and 3D positioning errors by 8.5% and 8.7% over 180 epochs, respectively, against the conventional delayed-locked loop (DLL). [ABSTRACT FROM AUTHOR]

Integer ambiguity resolution enabled precise point positioning, PPP-RTK, which is becoming one of the most popular global navigation satellite system (GNSS) positioning modes. Owing to the presence of rank deficiencies in the system of GNSS observation equations, one needs to choose some of the GNSS parameters as S-basis and let the remaining parameters absorb them. Doing so forms a full-rank PPP-RTK model whose combined parameters are estimable. To simplify the model construction, previous contributions assume that observations are tracked on common-frequency (CF) bands for all the involved receiver-satellite pairs. Such a model is referred to as CF PPP-RTK. However, the coexistence of legacy and modernized GNSS signal systems, together with the presence of outdated and updated receiver firmware, leads to not-common-frequency (NCF) cases where some of the involved receivers fail to track observations on certain frequencies. For such cases, the CF PPP-RTK model discards part of the observations so as to maintain the CF assumption. In this contribution, we refrain from making the CF assumption and extend the GNSS undifferenced and uncombined formulation to NCF cases. Such a NCF PPP-RTK model ensures that all observations contribute to the parameter estimation process, avoiding losing any information content in the data. As a result, our proposed NCF PPP-RTK avoids any potential reduction in both the availability and the precision of the corrections. To evaluate the positioning performance of the proposed model, we conducted three experiments with continuously operating reference station data in Hong Kong, Australia, and Europe. The superiority of the NCF PPP-RTK model over its conventional CF PPP-RTK version is illustrated in terms of both the time-to-first-fix and root mean square positioning errors. [ABSTRACT FROM AUTHOR]

The Choushui River Alluvial Fan (CRAF) is a major agricultural area in Taiwan with heavy groundwater usage. The extraction of groundwater here has caused land subsidence, which is now a significant global environmental issue. This study analyzes land subsidence in the CRAF by integrating hydrogeological data from 233 groundwater monitoring stations across four aquifers (CRAF Groundwater_NET) and data from 50 continuous GNSS stations (CRAF GNSS_NET). We developed an automated processing flow for GNSS static surveying within CRAF GNSS_NET, and further employed a time-series fitting method to examine the long-term trends and annual changes for both GNSS and groundwater level data. Our analysis of the time-series data from the past decade identifies areas of significant groundwater level depletion and subsidence hotspots. We explore the relationship between groundwater level variations and surface displacements within CRAF, utilizing GNSS data to analyze horizontal and vertical displacement trends, as well as annual changes. We integrate these findings with hydrogeological data to understand regional subsidence patterns. Our results indicate that CRAF is characterized by distinct hydrogeological features. The study finds that the amplitudes of annual changes in both groundwater level and vertical displacement generally increase from northeast to southwest in the analyzed region. One particular area shows significant groundwater level decline, with the most severe rate recorded at 0.54 m/year. Similarly, GNSS analysis indicates pronounced subsidence trends in the same area, with rates ranging from 4.2 to 5.2 cm/year. These findings highlight the critical need for the development of effective groundwater management strategies to ensure sustainable use of groundwater resources and to implement mitigation measures against land subsidence in similar multipleaquifer settings. [ABSTRACT FROM AUTHOR]

[Objectives] To monitor the stability of open-pit coal mine slopes in real time and ensure the safety of coal mine production. [Methods] The automatic monitoring system of coal mine slope was explored in depth, and the core functions of the system were designed comprehensively. According to the design function of the automatic monitoring system, the slope automatic monitoring system was constructed. Besides, in accordance with the actual situation of the slope, the monitoring frequency of slopes was set scientifically, and the key indicators such as rainfall, deep displacement and surface displacement of the slopes were monitored in an all-round and multi-angle way. [Results] During the monitoring period, the overall condition of the slope remained good, and no landslides or other geological disasters occurred. At the same time, the overall rainfall in the slope area remained low. In terms of monitoring data, the horizontal displacement and settlement of the slopes increased first and then tended to be stable. Specifically, the maximum horizontal displacement during the monitoring period was 22.74 mm, while the maximum settlement was 18.65 mm. [Conclusions] The automatic slope monitoring system has obtained remarkable achievements in practical application. It not only improves the accuracy and efficiency of slope stability monitoring, but also provides valuable reference experience for similar projects. [ABSTRACT FROM AUTHOR]

Medium‐scale traveling ionospheric disturbances (MSTIDs) can significantly alter a region's ionosphere features, severely impacting the performance and stability of services such as shortwave communication and navigation positioning. By utilizing the total electron content (TEC) data from BeiDou geostationary satellites for 2022–2023, this study investigated the characteristics of MSTIDs over Hong Kong concerning local time and seasons. A total of 622 MSTID events were observed, classified into three types: daytime (10:00–17:00 LT), twilight (17:00–22:00 LT), and nighttime (22:00–02:00 LT). The occurrence rates and excitation mechanisms of the three types of MSTIDs were analyzed. Daytime and twilight MSTIDs had higher occurrence rates during winter, while nighttime MSTIDs had higher occurrence rates in summer and were even absent during winter. Overall, daytime MSTIDs were the most common, followed by twilight MSTIDs, while nighttime MSTIDs were less frequent. The propagation directions of MSTIDs exhibited anisotropy but showed some clustering patterns. Daytime MSTIDs exhibited high directional diversity during summer, but more concentrated in winter. Nighttime MSTIDs, on the other hand, were more focused during summer. It is worth noting that twilight MSTIDs exhibit similar climatological characteristics to daytime MSTIDs, which have not been observed in previous studies. It is suggested that daytime MSTIDs in the Hong Kong region are likely primarily generated by atmospheric gravity waves (AGWs) from low‐latitude regions, while nighttime MSTIDs are likely caused by Perkins instability. Twilight MSTIDs may originate from AGWs at the solar terminator, as well as daytime MSTIDs propagated from mid‐latitude areas. Key Points: MSTIDs during daytime, twilight, and nighttime over Hong Kong are statistically analyzed for the first time using BeiDou GEO satellitesThe occurrence of MSTIDs shows significant seasonality and local time dependence, with propagation directions exhibiting anisotropyTwilight MSTIDs display propagation characteristics similar to daytime MSTIDs, possibly related to AWGs generated at the solar terminator [ABSTRACT FROM AUTHOR]

Mobile robots have been widely engaged in many fields. To obtain the precise and consistent localization of mobile robots, the Global Navigation Satellite System (GNSS) is often employed. With the continuous development and modernization of GNSS, more tracked satellites can be used for multi-GNSS positioning calculation, which can improve the positioning performance and enhance accuracy. However, it also increases computational complexity. Therefore, a satellite selection method, which selects a subset from all visible satellites, is necessary. In multi-GNSS positioning, the geometric dilution of precision (GDOP) is an essential metric for satellite selection. However, the traditional traversal method requires a large amount of solution resources. In this paper, we proposed an improved genetic algorithm for satellite selection. By defining the maturity factor (MF) to guide the crossover and mutation operators, the search performance is guaranteed while reducing unnecessary crossover and mutation operations, thus reducing the search time. By adopting the previous epoch optimal individual inheritance strategy, the satellite selection results of subsequent epochs under continuous epochs have been improved. The experimental results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper proposes an improved initial alignment method for a strap-down inertial navigation system/global navigation satellite system (SINS/GNSS) integrated navigation system with large misalignment angles. Its methodology is based on the three-dimensional special Euclidean group and extended Kalman filter (SE2(3)/EKF) and aims to overcome the challenges of achieving fast alignment under large misalignment angles using traditional methods. To accurately characterize the state errors of attitude, velocity, and position, these elements are constructed as elements of a Lie group. The nonlinear error on the Lie group can then be well quantified. Additionally, a group vector mixed error model is developed, taking into account the zero bias errors of gyroscopes and accelerometers. Using this new error definition, a GNSS-assisted SINS dynamic initial alignment algorithm is derived, which is based on the invariance of velocity and position measurements. Simulation experiments demonstrate that the alignment method based on SE2(3)/EKF can achieve a higher accuracy in various scenarios with large misalignment angles, while the attitude error can be rapidly reduced to a lower level. [ABSTRACT FROM AUTHOR]

Precise point positioning-real-time kinematic (PPP-RTK) positioning combines the advantages of PPP and RTK, which enables the integer ambiguity resolution (IAR) without requiring a reference station nearby. The ionospheric corrections are delivered to users to enable fast IAR. For large-scale networks, precise interpolation of ionospheric delays is challenging. The ionospheric delays are often independently estimated by the user, in the so-called ionosphere-float mode. The augmentation of low Earth orbit (LEO) satellites can bridge this shortcoming thanks to their fast speeds and the resulting rapid geometry change. Using 30-s real dual-frequency Global Positioning System (GPS) and Beidou Navigation Satellite System (BDS) observations within a large-scale network of thousands of kilometers, this contribution tests the effects of LEO augmentation using simulated dual-frequency LEO signals from the navigation-oriented LEO constellation, CentiSpace. Results showed that the LEO augmentation makes the solution convergence less sensitive to the original Global Navigation Satellite System (GNSS)-based model strength. The improvements in the convergence times are significant. For example, in the kinematic mode, the convergence time of the 90% lines of the GPS/BDS-combined ambiguity-float horizontal solutions to 0.05 m is shortened from more than 60 to 3.5 min, and that of the GPS-only partial ambiguity resolution (PAR)-enabled horizontal solutions is shortened from more than 20 to 4.5 min. In both the ambiguity-float and PAR-enabled cases, the 68.27% (1σ) lines of both the kinematic and static horizontal and height errors can converge to 0.05 m within 4 min, and for the 90% lines, within 6.5 min in all cases. The 90% line of the GPS/BDS/LEO combined PAR-enabled solutions can converge to 0.05 m within 2.5 and 3 min in the horizontal and up direction, respectively. Results also showed that enlarged projection of the mismodeled biases on the user coordinates were observed in the LEO-augmented scenario after convergence or ambiguity resolution. This is mainly due to the lower orbital height and low elevation angles of the LEO satellites, which requires further research when real LEO navigation signals are available. [ABSTRACT FROM AUTHOR]

The triple-frequency global positioning system (GPS), BeiDou navigation satellite system-3 (BDS-3), and Galileo can form the geometry-free and ionosphere-free (GFIF) carrier phase and pseudorange combinations, respectively. These combinations provide a precondition for which the accuracies of the carrier phase and pseudorange observations can be evaluated, respectively. The stochastic model of precise point positioning (PPP) processing is constructed using the evaluated results. The 176 International GNSS Service (IGS) stations are used to validate the presented method. The evaluated results show that accuracies of the GPS, BDS-3, and Galileo carrier phase observations are at the millimeter level, while those of pseudorange observations reach the decimeter level. In addition, BDS-3, GPS, and Galileo have different precisions. The stochastic model, which is reestablished from the evaluated accuracies, is tested using single Global Navigation Satellite System (GNSS) and multiGNSS PPP performances. The single-GNSS PPP shows that its convergence time has a mean improvement of 24%, and its 1- and 2-h mean three dimensions (3D) positioning accuracies are improved by about 17.7% and 4.5%, respectively, compared with those of empirical accuracies-based stochastic models. It also has the best performance in the multiGNSS PPP. Its mean convergence time of GPS+Galileo for 3 days is shorter than 35 min, while that of GPS+BDS-3 is less than 30 min. The mean improvements for the convergence time and 1- and 2-h 3D positioning reach 28%, 9.4%, and 2.8%, respectively, when the GPS+Galileo and GPS+BDS-3 PPP use the reestablished stochastic model instead of the empirical methods. [ABSTRACT FROM AUTHOR]

In complex urban, port, and factory environments, GNSS and UWB encounter significant challenges from signal blockage and multipath effects. This study proposes a GNSS-RTK/WLR-UWB tight integration positioning method, utilizing Weighted Linear Regression to fit missing UWB epochs and introducing dynamic weight adjustment. The track cart and pedestrian experiment demonstrates that the single-epoch positioning accuracy is improved by 53.47%, 65.94%, and 28.03% in E, N and U compared to RTK. The filtering positioning achieves accuracy better than 1 cm in E and N, with a high ambiguity resolution success rate exceeding 99.40%, and reduces time-to-first-fix from 6-13 s to 3 s. [ABSTRACT FROM AUTHOR]

Objectives: In recent years, the climate change in Xinjiang region, China is complex. It is of great significance to study the terrestrial water storage (TWS) and its load deformation for the accurate maintenance of the regional reference frame. Methods: The satellite gravity data GRACE (gravity recovery and climate experiment) was used to invert the changes of land water storage in Xinjiang region from 2010 to 2014, and the independent component analysis was used to decompose it into spatiotemporal models, and the spatial characteristics of multiple time scales were analyzed. On this basis, the correction on the first-order of gravity potential coefficient and load Love number is carried out, the correction of the non-tidal atmospheric and ocean model (GAC) from GRACE is introduced to obtain the vertical change of the crust caused by the migration of the land water load. The GRACE inversion results are corrected by scale factor method derived from WaterGAP global hydrology model (WGHM). The influence of deformation is analyzed by introducing monthly precipitation data from global precipitation climatology project. And the deformation displacements of the 13 continuously operating reference system stations in the survey area are quantitatively compared. The correlation between TWS load signal of each station and the annual vertical displacement of global navigation satellite system (GNSS) is analyzed. Results: The results show that TWS in Xinjiang region presents multi-time scale characteristics, with obvious annual variation and long-term trend. The annual change is particularly significant near the western Pamirs Plateau, and the trend term is reflected in the long-term decrease year by year. The signal is relatively strong in the western Urumqi and Tianshan Mountains. In general, the change of land water load causes the vertical displacement of the crust in the study area, and the time series shows a small fluctuation with an amplitude of -1.5-1.5 mm, which is consistent with the deformation results of WGHM model. In addition to the obvious time lag, the time series of TWS load deformation and precipitation change are consistent with the overall trend. After GAC correction, the consistency between GRACE results and GNSS vertical displacement was enhanced, and the correlation coefficient and weighted root mean square (WRMS) were significantly improved. The correlation coefficient of each station was 0.63-0.91, and WRMS was 16.18%-58.97%. Conclusions: The research method in this paper can reveal more detailed hydrological signal characteristics in Xinjiang region, and the research results can provide important technical support for accurate maintenance of regional reference frame. [ABSTRACT FROM AUTHOR]

Ionosphere has important influences on the performances of Global Navigation Satellite System (GNSS) in terms of signal quality and ranging errors. This study discusses the impact of ionosphere disturbances caused by the solar flare and geomagnetic storm events in September 2017 and October 2021 on signal quality and positioning accuracy. To identify the occurrence and also to study the magnitude of the storm, we have evaluated the Solar Activity parameters and constructed global Rate of TEC Index maps. In regard of the GNSS signal, both the signal-in-space ranging error and cycle slip occurrence are adopted to study the influence of the solar flare on the accuracy of the broadcast ephemeris and the quality of phase observation. Furthermore, the kinematic precise point positioning experiments with 39 International GNSS Service (IGS) stations are carried out, and the positioning errors of north, east, and up components are calculated to assess the precise positioning accuracy during the storm. The presented results suggest that the kinematic precise point positioning accuracy of the selected IGS stations in low- and high-latitude areas degraded at 8th September 2017 and 12th October 2021, implying that the GNSS precise positioning are less reliable during the solar flare events. [ABSTRACT FROM AUTHOR]

FORMOSAT-7/COSMIC-2 was launched in June 2019 and provides high spatial resolution radio occultation (RO) profile data. The data can be beneficial for weather and climate studies and increase the accuracy of weather forecasts. This study aims to assess the two-year COSMIC-2 RO-PWV (precipitable water vapor) accuracy. Ten years of GNSS-PWV data inverted from PPP (precise point positioning) are better than those from the DD (double difference) method when taking radiosonde-observed data as the true reference values in Taiwan. Hence, in this study, GNSS-PWV from PPP is compared with COSMIC-2 RO-PWV to verify the accuracy of RO-PWV. Removing the elevation of the lowest point of an RO event above 5 km can prevent an RO event with an error exceeding 40 mm. The mean GNSS-PWV is higher than the mean RO-PWV, which are 45.7 mm and 39.9 mm, respectively, from 2020 to 2021. RO-PWV derived from COSMIC-2 in 2020 and 2021 is underestimated when taking GNSS-PWV as a reference. The mean RO error is 6.8 mm, and the mean error on land is higher than that on the ocean, with magnitudes of 8.0 mm and 6.6 mm, respectively. The higher RO-PWV accuracy on the ocean than on land is one of the reasons for the higher RO-PWV accuracy for RO events matched at the Japan GEONET stations (99.2 % on the ocean; mean error of 6.1 mm) than that at the Taiwan CWB stations (68.2 % on the ocean; mean error of 7.7 mm). In the monthly mean RO-PWV data from 2020 to 2021, the RO-PWV and its error show seasonal variations, with high values in summer (51.0 ± 9.2 mm) and low values in winter (31.9 ± 5.0 mm). The seasonal trend of RO-PWV is consistent with that of temperature. Here, we verify that the accuracy of COSMIC-2 RO-PWV is comparable to that of GNSS-PWV. [ABSTRACT FROM AUTHOR]

One of the main methods of the path localization of moving objects is positioning using Global Navigation Satellite Systems (GNSSs) in cooperation with Inertial Navigation Systems (INSs). Its basic task is to provide high availability, in particular in areas with limited access to satellite signals such as forests, tunnels or urban areas. The aim of the article is to carry out the testing and analysis of selected navigation parameters (3D position coordinates (Northing, Easting, and height) and Euler angles (pitch and roll)) of the GNSS/INS system for Unmanned Surface Vehicle (USV) path localization during inland hydrographic surveys. The research used the Ellipse-D GNSS/INS system working in the Real Time Kinematic (RTK) mode in order to determine the position of the "HydroDron" Autonomous Surface Vehicle (ASV). Measurements were conducted on four representative routes with a parallel and spiral arrangement of sounding profiles on Lake Kłodno (Poland). Based on the obtained research results, position accuracy measures of the "HydroDron" USV were determined using the Ellipse-D GNSS/INS system. Additionally, it was determined whether USV path localization using a GNSS/INS system working in the RTK mode meets the positioning requirements for inland hydrographic surveys. Research has shown that the Ellipse-D system operating in the RTK mode can be successfully used to position vessels when carrying out inland hydrographic surveys in all International Hydrographic Organization (IHO) Orders (Exclusive, Special, 1a/1b and 2) even when it does not work 100% correctly, e.g., loss of RTK corrections for an extended period of time. In an area with limited coverage of the mobile network operator (30–40% of the time the receiver operated in the differential mode), the positioning accuracy of the "HydroDron" USV using the Ellipse-D GNSS/INS system working in the RTK mode was from 0.877 m to 0.941 m for the R95(2D) measure, depending on the route travelled. Moreover, research has shown that if the Ellipse-D system performed GNSS/INS measurements using the RTK method, the pitch and roll error values amounted to approx. 0.06°, which is almost identical to that recommended by the device manufacturer. However, when working in the differential mode, the pitch and roll error values increased from 0.06° to just over 0.2°. [ABSTRACT FROM AUTHOR]

PPP-RTK combines the advantages of both precise point positioning (PPP) and real-time kinematic (RTK) techniques. While constructing PPP-RTK models based on undifferenced and uncombined observations offers apparent benefits, these observation equations suffer from a rank deficiency issue. To address this problem, the Singularity-system (S-system) theory can be utilized. This theory imposes constraints on a minimal subset of parameters, known as the S-basis, by setting them to arbitrary values, typically zeros. Despite the existence of multiple options for the S-basis, prevailing research conventionally selects the parameters of one receiver—the pivot—as the S-basis. In this study, we depart from this practice by selecting the mean of receiver-related parameters as the S-basis. This departure prompts an exploration into how the S-basis choices influence PPP-RTK outcomes regarding network product precision and user positioning performance. Our comparative analysis of the mean receiver (MR) and pivot receiver (PR) models unveils distinctions in the combined product precision. These products include satellite clocks, satellite phase biases, and ionospheric delays (excluding tropospheric delays). The distinction emerges because the estimable satellite clocks in the PR model incorporate atmospheric delays specific to the pivot receiver, in contrast to the MR model, which integrates mean atmospheric delays from all receivers. Despite the distinction in the analytical form of combined product and its precision, both model results in similar positioning performance. This is because variations in product precision levels caused by selecting different atmospheric parameters as the S-basis can be nullified by the parameterized atmospheric delays on the user side. With the inclusion of tropospheric delays, the PR and MR models also demonstrate similar performance and yield more accurate user positioning when located near the pivot receiver compared to positions farther from the pivot receiver when employing ambiguity-float network products. This dependence on the pivot receiver stems from both models selecting the pivot receiver ambiguities as the S-basis, while opting for mean ambiguities across all receivers negates the integer nature of ambiguities. Our conclusion underscores that identical positioning outcomes in PR and MR PPP-RTK models rely on both models selecting the same ambiguities as the S-basis. This highlights the potential variability in PPP-RTK performance when different ambiguity parameters are selected as the S-basis, particularly in the absence of network integer ambiguity resolution. [ABSTRACT FROM AUTHOR]

PPP–RTK, a synthesis of precise point positioning (PPP) and real-time kinematic (RTK) techniques, achieves fast integer ambiguity resolution-enabled positioning using, among others, satellite clocks, biases, and ionospheric corrections generated in a reference network. When formulating a network model to estimate these products, one usually considers a receiver as the pivot and selects its receiver-related parameters as the datum to address the rank deficiency problem. This work demonstrates that the precision of ambiguity-float combined PPP–RTK products relates to the pivot receiver selection. The combined product encompasses the summation of satellite clocks, satellite phase biases, and ionospheric delays at a certain station. Specifically, we find that the precision of ambiguity-float combined products at the pivot receiver surpasses that at non-pivot receivers by a significant margin. Consequently, user positioning becomes inhomogeneous in the network, as users far away from the pivot receiver perform worse than those close to the pivot receiver. To relieve this pivot receiver dependency, we emphasize the necessity of network integer ambiguity resolution, which improves the precision of products and ensures the homogeneity of user positioning. For verification purposes, we performed a one-week experiment involving 12 global positioning system (GPS) receivers to generate network products and 23 receivers to perform user positioning. The results showed that the precision of ambiguity-float combined products at the pivot receiver was better than 2 cm, whereas that at non-pivot receivers reached several decimeters. With these ambiguity-float products employed on the user side, the time-to-first-fix (TTFF) of the positioning near the pivot receiver was less than 5 epochs, but that away from the pivot receiver exceeded 15 epochs. Network integer ambiguity resolution improved the quality of PPP–RTK products, as the precision of combined products at an arbitrary receiver reached several millimeters. User positioning with ambiguity-fixed products became homogeneous with an average three-dimensional root-mean-square (3D RMS) of 1.5 cm, and the mean TTFF decreased to 4 epochs. [ABSTRACT FROM AUTHOR]

The vulnerability of civil receivers of the Global Satellite Navigation System (GNSS) to spoofing jamming has raised significant concerns in recent times. Traditional multi-antenna spoofing detection methods are limited in application scenarios and come with high hardware costs. To address this issue, this paper proposes a novel GNSS spoofing detection method utilizing three low-cost collinear antennas. By leveraging the collinearity information of the antennas, this method effectively constrains the observation equation, leading to improved estimation accuracy of the pointing vector. Furthermore, by employing a binary statistical detection model based on the sum of squares (SSE) between the observed value and the estimated value of the pointing vector, real-time spoofing signal detection is enabled. Simulation results confirm the efficacy of the proposed statistical model, with the error of the skewness coefficient not exceeding 0.026. Experimental results further demonstrate that the collinear antenna-based method reduces the standard deviation of the angle deviation of the pointing vector by over 55.62% in the presence of spoofing signals. Moreover, the experiments indicate that with a 1 m baseline, this method achieves 100% spoofing detection. [ABSTRACT FROM AUTHOR]

The time difference RTK (TDRTK) of GNSS can obtain high-precision baseline constraints to control the cumulative error of dead reckoning technology. However, the availability of traditional TDRTK decreases sharply with the increase of time interval. A geometry-free TDRTK method with quality control using multi-frequency observations is proposed to solve this problem. Experimental shows that in the dynamic condition of a stand-alone GNSS receiver, the average and maximum relative position accuracy (10 min and 10 kilometres tests) of the proposed method are improved by 42.2% and 44.2% compared with the existing methods. [ABSTRACT FROM AUTHOR]

Multipath frequencies need to be estimated for tide level inversion from Global Navigation Satellite System Reflectometry (GNSS-R) signals. However, conventional inversion methods only estimate principal frequency, which results in low data utilization and insufficient temporal resolution of the inversion results. Here, we use the Savitzky-Golay (SG) smoothing filtering to optimize the GNSS-R tide level inversion. First, the Lomb-Scargle Periodogram (LSP) is used to extract the first four frequencies (f1f4) of signal power, which are then inverted for their corresponding tide level values. Then the SG smoothing filtering is used to extract the best inversion results. Finally, the 30-day data from BRST and MAYG stations in France are used to verify the effectiveness of the approach. The results show that, compared with LSP method, the proposed approach increases the number of daily average inversion values by 34. 3% and 19.6%, and reduces the maximum time interval of inversion values by 43. 2% and 29.4%, for BRST station and MAYG station, respectively; compared with window LSP (WINLSP) method, the pro- posed approach increases the number of daily average inversion values of BRST station and MAYG station by 24.2% and 45.9%, decreases the maximum time interval of inversion values by 25.4% and 28.6%, respectively, and reduces the RMSE by 7 cm for both stations. It can be concluded that this method increases the number of inver- sion results, raises the data utilization and improves the temporal resolution of tide level inversion besides adequate accuracy. [ABSTRACT FROM AUTHOR]

Atmospheric wet delay caused by Precipitable Water Vapor (PWV) significantly impacts the performance of many geodetic surveying systems such as Global Navigation Satellite System (GNSS). In this study, we use wet delay corrections forecast by the Weather Research and Forecasting (WRF) model to enhance GNSS Precise Point Positioning (PPP) during two observation periods with two different weather conditions, that is, period 1: March 01 to 14, 2020 (average PWV: 23.5 kg/m2) and period 2: June 02 to 15, 2020 (flooding weather with average PWV: 55.6 kg/m2), over the South China. PWV data from 277 to 263 GNSS stations are assimilated into WRF model to enhance the WRF water vapor forecasting capability for period 1 and period 2, respectively. Wet delay corrections from two different WRF configurations, that is, WRF no data assimilation and WRF with assimilation of GNSS PWV, are used to augment the PPP. Totally, eight WRF‐enhanced PPP schemes are tested. The results show that WRF‐enhanced PPP schemes generally have a better positioning performance in the up component than traditional PPP. After using WRF wet delay corrections, for static mode, the vertical positioning accuracy is improved by 14.6% and 33.7% for period 1 and period 2, respectively. The corresponding convergence time are reduced by 41.8% and 25.0% for period 1 and period 2, respectively. For kinematic mode, the positioning accuracy improvements in the up component reach 13.8% and 19.0% for period 1 and period 2, respectively. The kinematic PPP convergence time is reduced by up to 8.2% for period 1. Plain Language Summary: Global Navigation Satellite System (GNSS) signal is significantly delayed by the water vapor in the Earth's troposphere. How to mitigate this so‐called wet delay has long been a challenging problem in GNSS Precise Point Positioning (PPP) community. In this study, we use the Weather Research and Forecasting (WRF) model to simulate the distribution and variation of water vapor over the South China during two periods with different water vapor conditions, that is, period 1: March 01 to 14, 2020 (average PWV: 23.5 kg/m2) and period 2: June 02 to 15, 2020 (flooding weather with average PWV: 55.6 kg/m2). In addition, water vapor data from 277 and 263 GNSS stations have been assimilated into the WRF model for period 1 and period 2, respectively, to further improve WRF water vapor forecasting accuracy. The high‐quality water vapor forecasts are then used to correct the wet delay for GNSS PPP. Our results show that, with use of the wet delay corrections forecast by the WRF model, GNSS PPP can achieve a better performance in positioning accuracy and convergence speed during both two periods. Key Points: Weather Research and Forecasting (WRF)‐enhanced Precise Point Positioning (PPP) strategies improve positioning accuracy in the up component for both static and kinematic modesWRF‐enhanced PPP strategies accelerate static positioning convergence speed in the up componentWRF‐enhanced PPP strategies show a larger positioning accuracy improvement in wet period [ABSTRACT FROM AUTHOR]

In this paper, we investigate the possible mechanism behind the volcanic plume drag and the massive expansion of the ionospheric Total Electron Content (TEC) along the eastern longitudes by using near-field observations of the 15 January 2022 Hunga Tong-Hunga Ha'apai volcanic eruption. The meteorological omega parameter shows a dominant upward/downward movement of the air parcels along the eastern and southern sides of the volcanic eruption. This dominant air convection under the presence of the heavy moisture of volcanic plume and vector winds indicated the formation of a cyclone over and around the Tonga volcano. This cyclone dragged the heavy volcanic plume towards the eastern longitudes (150oE – 180oE). Moreover, we observe that the volcanic plume injected about 5 DU of Sulfur Dioxide (SO 2) and 30 kgm−2 of the water content along the total atmospheric column. The chain reactions of Hunga Tonga volcanic trace gases with the gases present in the neutral atmosphere instigated an air ionization process, while under the presence of the heavy water content, these ions underwent an ion-hydration process that contributed to the electrodynamical changes in the region. These electrodynamical changes can be regarded as Atmospheric Chemical Potential (ACP) in the lower atmosphere. We observe a sharp increase in the ACP of ∼0.26 eV along the eastern longitudes (160–180°E) exactly above the dragged volcanic plume area. The long-term TEC changes that have been observed towards the eastern longitudes are the result of the ion-hydration process at the lower atmosphere. The statistical analysis showed a critical change during the day of the event up to ∼48 TECU with an increasing value of 28 and 18 TECU from the lowest and highest ranges before the event over the crater, respectively. Our main findings showed ionospheric anomalies in the near field started from 6:00 to 16:00 UTC. Based on Swarm satellites, the S4 values have significant changes around 0.3–0.6 lasting for tens of minutes. [ABSTRACT FROM AUTHOR]

Accurate information about the satellite transmit antennas is essential for high-precision GNSS applications. Such metadata of the GPS III satellites were publicly made available by the manufacturer Lockheed Martin. They comprise phase center offsets (PCOs), phase patterns, and directivity patterns. These calibrations are validated with ground-based measurements of a global GPS tracking network and observations of a high-gain antenna. Phase center offsets and patterns are estimated from dual-frequency observations of a ground tracking network. The ionosphere-free L1/L2 z-PCOs show a 10 cm offset w.r.t. the manufacturer calibrations due to already known inconsistencies with the ITRF2020 scale fixed in the estimation. The standard deviation of the differences between estimated and calibrated z-PCOs is 2.7 cm. The estimated phase patterns have a 0.7 mm RMS consistency with the manufacturer calibrations after minimizing the raw patterns for nadir angles between 0° and 14°. The directivity patterns are validated with the effective isotropic radiated power (EIRP) measured with a 30 m high-gain antenna. The measured EIRP for the L1 and L2 band is affected by M-code transmission from a distinct antenna. When modeling the additional contribution of this antenna, the nadir-angle variation of the EIRP matches the calibrated directivity patterns with a precision of 0.1 dBW. Representative transmit power values of the main navigation antenna amount to 125 W, 30 W, and 85 W in the L1, L2, and L5 bands, while the L1 and L2 M-code signals are transmitted with about 30 W and 25 W, respectively. [ABSTRACT FROM AUTHOR]

Real-time kinematic (RTK) positioning of the global navigation satellite systems (GNSS) is used to provide centimeter-level positioning accuracy. There are several ways to implement RTK but a Kalman filter-based RTK is preferred because of its superior capability to resolve GNSS carrier phase integer ambiguities. However, the positioning performance of the Kalman filter-based RTK is often compromised by various factors when it comes to determining a precise relative position vector between moving unmanned aerial vehicles (UAVs) equipped with low-cost GNSS receivers and antennas, where the locations of both GNSS antennas are not accurately known and change over time. Some of the critical factors that lead to a high rate of incorrect resolutions of carrier phase integer ambiguities are measurement time differences between GNSS receivers, frequent cycle slips with high noise in code and carrier phase measurements, and an improper Kalman filter gain due to a newly risen satellite. In this paper, effective methods to deal with those factors to achieve a seamless Kalman filter-based RTK performance in moving UAVs are presented. Using our extensive 45 flight tests data sets, conducted over a duration of 3 to 12 min, the RTK positioning results showed that the root-mean-square position error (RMSE) decreased by up to 95.13%, with an average of 65.31%, and that the percentage of epochs that passed the ratio test, which is the most common method for validating double differenced carrier phase integer ambiguity resolution, increased by up to 130%, with an average of 23.54%. [ABSTRACT FROM AUTHOR]

The concurrent research compares the results of a geodetic baseline through Global Navigation Satellite System (GNSS) measurements with low-cost GNSS receivers, geodetic receivers, and additional electronic distance measurements (EDM) with a total station, in order to determine whether low-cost GNSS receivers and antennas are suitable for topographic–geodetic work depending on the precision obtained. Fifteen different campaigns were carried out (October 4–8, 2022) with five different combinations of receivers and antennas for the establishment of the baseline: geodetic GNSS equipment–geodetic GNSS equipment, geodetic GNSS equipment–low-cost GNSS kit, low-cost GNSS kit–geodetic GNSS equipment, low-cost GNSS receiver with geodetic antenna–low-cost GNSS receiver with geodetic antenna, and low-cost GNSS kit–low-cost GNSS kit. It is important to note that the low-cost GNSS kit includes the C099-F9P application board for ZED-F9P of U-Blox with patch antenna U-Blox ANN-MB-00 multiband GNSS antenna and ground plane. Similarly, another EDM campaign was realized (October 10, 2022) in order to carry out a statistical hypothesis test related to the length calculated through static relative positioning. The results show that all combinations fit with a certainty of 95% of similarity to the length of the EDM (39.6116 m) showing differences up to 5.1 mm. In relation to the coordinates, the maximum variations were found to be less than 1.2 cm and the azimuth showed similitude between them, which demonstrates that the distances, coordinates, and orientations are consistent with the final solutions of the geodetic GNSS equipment. [ABSTRACT FROM AUTHOR]

• Temporal correlation in RTK is considered using a Colored KF. • A hybrid control chart is proposed to construct RTK-RAIM for ramp faults. • A performance comparison with the baseline method is made via static and dynamic tests. For real-time kinematic (RTK) positioning in intelligent transportation systems (ITS), the slow-growing faults detection and exclusion (FDE) in carrier phase measurements with time-correlated satellite navigation data poses a significant challenge. In response, we propose the short-baseline RTK Receiver Autonomous Integrity Monitoring (RTK-RAIM), which utilizes a hybrid control chart with a colored Kalman filter for detecting small yet persistent faults. The hybrid control chart incorporates the windowed multivariate homogeneously weighted moving average and dual multivariate cumulative sum charts to accelerate fault detection. The fault exclusion is conducted using the solution separation. Experimental validation using static data and dynamic data in suburban and urban areas demonstrates the efficacy of RTK-RAIM in detecting ramp faults with time-correlated noise. Results show that Colored KF can attenuate the detection metrics in the fault-free case when measurements are time-correlated. The hybrid control chart, operating in an open environment, has the ability to detect carrier phase slope faults with a high probability, even when the slope is as small as 0.01cycle/s. It can also detect carrier-phase ramp faults whose gradient are 0.1cycle/s in an urban area. By enhancing the detection ability of FDE in RTK, this hybrid-control-chart-based RAIM promotes safer and more dependable performance in future ITS applications. [ABSTRACT FROM AUTHOR]

The demand for various emerging navigation-based technologies, particularly for autonomous and unmanned systems, has increased recently, requiring accurate and robust positioning performance to support these systems. While the global navigation satellite system is a key technology that can meet these demands, it faces significant challenges in urban areas due to multipath errors caused by tall buildings and signal obstructions. This study proposes a method for achieving precise absolute navigation in urban areas, even for users of low-cost, single-frequency receivers. To overcome these challenges, the proposed method utilizes the characteristics of multipath errors to ensure accurate navigation. As users move through urban areas, multipath errors tend to fluctuate and may cause frequent signal loss. The introduction of the “duration time” concept enables users to quickly select measurements with relatively small multipath errors based on the characteristics of multipath errors. Users can mitigate multipath errors by utilizing selected measurements and achieve more stable position estimation. By introducing duration time into time-differenced code-minus-carrier measurements and successfully selecting measurements using duration time, we confirmed that the navigation accuracy in urban areas can be improved. Field tests were conducted in an urban environment to verify the enhanced navigation performance of the proposed system. Hence, standalone navigation achieved meter-level performance, and integrated navigation combined with Doppler measurements achieved decimeter-level performance. This demonstrates that the proposed methods can mitigate position jumps caused by multipath errors in urban areas, ensuring stable position estimation performance.

The precise reconstruction of ionospheric electron density (IED) fields with high spatial and temporal resolutions has always been challenging. Global navigation satellite system (GNSS) tomography is a powerful tool to resolve the spatial structure and temporal behavior of IED. This study proposes a novel two-step algorithm of ionospheric tomography for the reconstruction of IED fields with high time resolution. Linear time-dependent ionospheric tomography model based on the node-based parameterization method is established for the first time. In the two-step reconstruction method, the linear trends of IED over a long time are first inverted. Then, the modeling residuals are adopted to obtain deviation terms. In addition, the design matrix is adaptively adjusted because the vertical variation parameter of IED for each voxel is dynamically updated from the IED profiles after each iteration. The tomography (5 min) is validated with GPS data collected over a one-month period (September 2020) from 629 stations in the USA. According to the GPS, COSMIC-2, and Swarm validations, the proposed tomography approach outperforms voxel-based, traditional node parameterization, and linear time-dependent methods by 10%–40%. The performance of the tomographic modeling is further examined by using a high geomagnetic activity period of April 20–29, 2023 in the high solar activity year. Results show that the tomographic model is robust even during severe geomagnetic storms.

Global navigation satellite system (GNSS)reflected signals have been widely used in remote sensing applications. To overcome the low-power budget of GNSS reflected signals, traditional detection strategies involve extending the coherent processing interval (CPI) of a single frame or employing the multiframe detection (MFD) method in which the noncoherent integration is used to accumulate echo energy. In this article, a novel coherent dynamic-programming-based track-before-detect (C-DP-TBD) algorithm is proposed to search and compensate for the interframe phase shift to improve the performance of weak target detection using GNSS reflected signals. The proposed algorithm is included in the two-stage MFD and follows a range-Doppler (RD) map generator. The RD map generator extracts the RD map candidate list for a specific data frame, which contains all of its variants based on the potential phase value and location shifts of the target peak in the RD domain relative to a designated reference frame. Subsequently, the C-DP-TBD processor coherently integrates each variant in this list with the reference frame, removes implausible variants, and selects the most reliable one by comparing all resulting peak signal-to-noise ratios with a preset threshold. The confirmation of the target track in the RD domain is finally achieved by extracting the position of the target peak from every available frame. Compared with traditional motion target detection methods with long CPI and DP-TBD methods, the performance superiority of the proposed algorithm is demonstrated by both simulation and experimental results in which a ferry was employed as a moving target.

Zenith tropospheric delay (ZTD), consisting of zenith hydrostatic delay (ZHD) and zenith wet delay (ZWD), is a significant contributor to errors in precise positioning using the global navigation satellite system (GNSS) precise point positioning (PPP) and real-time kinematic techniques. Accurate and timely predictions of ZTD on a global scale are crucial for enhancing GNSS positioning accuracy and expediting convergence. This study proposes an innovative global tropospheric prediction model that leverages long short-term memory (LSTM) neural networks, aiming to achieve both high precision and long-term prediction capability for ZTD. The experimental data utilized were sourced from the Vienna Mapping Functions 3-Optimized zenith total delay (ZTD) dataset. This study delves further into the analysis of ZTD residuals by extracting periodic signals. The ZTD residuals were then utilized to train a modified LSTM neural network model, enabling the prediction of global residuals. The final ZTD predictions were obtained by combining the modified LSTM ZTD residual forecast component with the ZTD periodic component. Our results demonstrate that the average root-mean-square error (RMSE) of the modified LSTM-ZTD model in 2020 was 1.44 cm. In addition, the average RMSE of the forecasted ZTD during spring, summer, autumn, and winter was found to be 1.43 cm, 1.47 cm, 1.56 cm, and 1.36 cm, respectively. Through the integration of the LSTM neural network and the ZTD periodic signal extracted using a physical algorithm, this work has successfully enhanced the accuracy and time span of ZTD forecasts on a global scale.

The jamming is found to increase significantly in recent years, and its impact is evident in Global Navigation Satellite System (GNSS) radio occultation (RO) measurements, such as those from COSMIC-2. This article presents an algorithm that applies the RO radiometry to detect and monitor long-term variations of GNSS jamming power from a deeply occulted height (HSL = −140 km). At these heights, the RO signal amplitude is at its noise level because the GNSS transmitter is far behind the Earth shadow. Thus, any enhanced RO amplitudes from these heights are considered as a jamming signal. The algorithm was successfully applied to two conflict zones: Mediterranean Sea and Middle East and Central Africa, where the Global Position System (GPS) jamming was frequently used by state-sponsored electronic warfare. The time series of normalized RO amplitude in these regions show a steady increase of the GPS jamming power since 2017, but a sharp decrease since the start of Russo–Ukrainian War.

Interferometric synthetic aperture radar (InSAR) techniques can be used to derive spatially dense “relative” measurements of vertical land motion (VLM), whereas global navigation satellite system (GNSS) provides point-based “absolute” measurements of VLM. The combination of GNSS and InSAR observations can yield spatially dense VLM measurements in an absolute reference frame. In addition, GNSS observations can be used to correct atmospheric noise in InSAR deformation measurements and serve as a complementary measure to isolate deep and shallow subsidence components. Given the increasing spatial and temporal coverage available from InSAR satellites, there is a need to establish calibration/validation networks that enable the use of InSAR for measuring VLM in coherence-challenged areas such as many low-lying coastal lands. In this study, we provide a method for the selection of sites for new GNSS installations such that the resulting GNSS network can better serve as tie points and validation for InSAR in areas where low coherence prevents high-fidelity phase unwrapping. Our method is applied in a case study for expanding the existing GNSS network in southern Louisiana, using abandoned oil well sites as potential sites. Considering practical limitations, distribution among various land classes, and following National Geodetic Survey guidelines, our proposed GNSS network consists of 61 (45 existing + 16 new) stations spread over a 50 000 km2 area of southern Louisiana.

The ionospheric disturbances induced by the Falcon 9 rocket launch on 17 January 2016 were reconstructed by three-dimensional computerized ionospheric tomography using observations from the North American global navigation satellite system networks. The results showed that concentric traveling ionospheric disturbances (CTIDs) occurred ∼18 min after the rocket launch and were remarkable at 200–300 km altitudes. The vertical phase velocities of the CTIDs were consistent with the inclinations of the U-shaped structures. At specific azimuth directions of 350°, 30°, and 105°, the estimated vertical phase velocities between 100 and 200 km altitudes were ∼222.2, ∼208.3, and ∼242.4 m/s, respectively. When the CTIDs propagated upward to 400–500 km altitudes, their vertical velocities increased to ∼566.7, ∼966.7, and ∼944.4 m/s. CTIDs traveling northward (azimuths 350°, 30°) had periods of ∼11 min. At 200 and 300 km altitudes, their horizontal phase velocities were ∼309.9–323.3 and ∼309.4–330.9 m/s, respectively, with horizontal wavelengths of ∼204.5–213.4 and ∼204.2–218.4 km. In contrast, CTIDs propagating eastward (azimuth 105°) displayed a period of ∼15 min. At 200 and 300 km altitudes, their horizontal phase velocities were ∼223.2 and ∼241.1 m/s, respectively, with horizontal wavelengths of ∼200.9 and ∼217.0 km. These CTIDs propagation characteristics agreed well with the theory of gravity waves.

This article provides a comprehensive analysis of Ukraine’s satellite navigation development, focusing on the evolution of its legal frameworks in the context of ongoing regional conflict. It examines historical and current aspects of Global Navigation Satellite System (GNSS) development in Ukraine, highlighting the intersection of technological innovation, international cooperation, and Ukraine’s role in global space initiatives. Special attention is paid to the 2023 bill “On State Regulation in the Sphere of Satellite Navigation,” emphasizing its critical role in national security and defense. The article underlines the need for robust legal and regulatory structures, professional expertise, and public-private collaboration to adapt to rapid industry changes and integrate effectively into the global space market.

The vertical profile of the ionosphere density plays a significant role in the development of low-latitude Equatorial Plasma Bubbles (EPBs), that in turn lead to ionospheric scintillation which can severely degrade precision and availability of critical users of the Global Navigation Satellite System (GNSS). Accurate estimation of ionospheric delays through vertical electron density profiles is vital for mitigating GNSS errors and enhancing location-based services. The objective of this study is to propose a neural network, trained with radio occultation data from the COSMIC-1 mission, that generates average ionospheric electron density profiles during dusk, focusing on the pre-reversal enhancement of the zonal electric field. Results show that the estimated profiles exhibit a clear seasonal pattern, and reproduce adequately the climatological behavior of the ionosphere, thus presenting strong appeal on ionospheric error attenuation.