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Landslides pose significant threats to life and property, particularly in mountainous regions. To address this, this study develops a landslide susceptibility model integrating Earth Observation (EO) data, historical data, and Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) ground movement results. The model categorizes areas into four susceptibility classes (from Class 1 to Class 4) using a multi-class classification approach. Results indicate that the Xtreme Gradient Boosting (XGB) model effectively predicts landslide susceptibility with area under the curve (AUC) values ranging from 0.93 to 0.97, with high accuracy of 0.89 and a balanced performance across different susceptibility classes. The integration of MT-InSAR data enhances the model's ability to capture dynamic ground movement and improves landslide mapping. The landslide susceptibility map generated by the XGB model indicates high susceptibility along the Pacific coast. The optimal model was validated against 272 historical landslide occurrences, with predictions distributed as follows: 68 occurrences (25%) in Class 1, 142 occurrences (52%) in Class 2, 58 occurrences (21.5%) in Class 3, and 4 occurrences (1.5%) in Class 4. This study highlights the importance of considering temporal changes in environmental conditions such as precipitation, distance to streams, and changes in vegetation for accurate landslide susceptibility assessment. [ABSTRACT FROM AUTHOR]

Monitoring of dam reservoirs is crucial for developing effective management strategies especially in regions with slope instabilities. Recent developments in satellite synthetic aperture radar (SAR) sensors and their processing techniques enabled frequent observations, allowing monitoring of landslides and revealing the triggering factors. In this study, we analyzed the slope movements in Kalekoy dam reservoir built in 2018 in Bingol Province, Türkiye using weekly Sentinel-1 SAR time series data. We used LiCSAR (Looking into Continents from Space with SAR) products freely served by the COMET-LiCS (Center for the Observation and Modeling of Earthquake Volcanoes and Tectonics) web portal to perform interferometric SAR (InSAR) time-series analysis. Using land use land cover, snow and vegetation indices derived from the Sentinel-2 optical imagery, and combining with precipitation, lake level measurements, and seismic and anthropogenic activities between 2015 and 2022, our findings revealed that the use of SAR data with regular global coverage is essential for deformation monitoring in dam reservoirs and ensure a comprehensive understanding of landslide phenomena in regions prone to such events. The slope movements were clearly observable in the InSAR time series with seasonal cycles especially in winter, and changes of snow cover were linked to them. Vegetation cover decreased over time in the region, likely influenced by the dam reservoir. Sudden changes in slope deformations were related to lake water levels and spring snowmelt as the saturation of landslide toe zones increased pore water pressure. Despite varying characteristics, changes in lake water levels and snowmelt were common triggers for all landslides analyzed. [ABSTRACT FROM AUTHOR]

Global Navigation Satellite Systems (GNSS) has become an essential component in modern times for positioning, navigation, and timing. A fast-growing economic region in Malaysia required a GNSS-based augmentation positioning and navigation service. To improve navigation solution, several augmentation techniques exist, such as a differential Global Positioning System (DGPS) assisted by reference station, or augmentation service provided by commercial communication satellite. The DGPS correction is applied through a real-time communication medium and can be received at the user side by several communication methods including internet-based, and this method is favourable for land and near-coast areas. This case study aims to investigate the reliability of internet-based DGPS and SBAS along the Peninsular Malaysia. A test was conducted and data were collected over 15 hours at a rate of 1 Hz from the available GNSS satellite using a geodetic-grade receiver mounted on a moving vehicle. The obtained results showed that DGPS and SBAS perform better than the navigation solution with an accuracy of 1.536 m and 0.955 m respectively, compared to the navigation solution with an accuracy of 3.159 m. The limitations of both augmentation techniques were also analysed and discussed in this study. [ABSTRACT FROM AUTHOR]

SBAS systems are applied in precise positioning of UAV. The paper presents the results of studies on the improvement of UAV positioning with the use of the EGNOS+SDCM solutions. In particular, the article focuses on the application of the model of totaling the SBAS positioning accuracy to improve the accuracy of determining the coordinates of UAVs during the realisation of a test flight. The developed algorithm takes into account the position errors determined from the EGNOS and SDCM solutions. as well as the linear coefficients that are used in the linear combination model. The research was based on data from GPS observations and SBAS corrections from the AsteRx-m2 UAS receiver installed on a Tailsitter platform. The tests were conducted in September 2020 in northern Poland. The application of the proposed algorithm that sums up the positioning accuracy of EGNOS and SDCM allowed for the improvement of the accuracy of determining the position of the UAV by 82-87% in comparison to the application of either only EGNOS or SDCM. Apart from that, another important result of the application of the proposed algorithm was the reduction of outlier positioning errors that reduced the accuracy of the positioning of UAV when a single SBAS solution (EGNOS or SDCM) was used. The study also presents the effectiveness of the proposed algorithm in terms of calculating the accuracy of EGNOS+SDCM positioning for the weighted average model. The developed algorithm may be used in research conducted on other SBAS supporting systems.

User differential range error (UDRE) is used to bound satellite clock and orbit errors in satellite-based augmentation system (SBAS). The code carrier incoherence (CCI) originated from satellite payload faults may degrade generated satellite corrections and corresponding UDRE/DFRE bounding. To ease the burden on UDRE caused by the CCI induced ranging error, a code carrier coherence (CCC) monitor is implemented. With SBAS evolving towards L1-L5 dual-frequency multi-constellation direction, ionosphere-free smoothing is preferred for both ground and airborne data processing, saving the great effort of bounding the ionosphere correction. Due to the more pronounced CCI fault in the L5 signal compared to the L1 signal, its impact on user positioning is magnified. It has been analyzed that the presence of satellite clock failure CCI fault does not undermine the accuracy of the generated satellite corrections. However, to enhance the system availability, the satellite clock failure should be considered and a dual-frequency CCC monitor is required to monitor the measurements from both frequencies, while excluding the effects of ionosphere delay. One solution is to add another L1-like monitor for monitoring the additional L5 signal. Since only ionosphere-free errors need to be bounded in the dual-frequency system, an ionosphere-free monitor is another choice. Furthermore, a chi-squared monitor is proposed combining of three ionosphere-free statistics to monitor both frequencies simultaneously. These options are compared on the protected fault space and the performance on the probability of missed detection. It is concluded that the chi-squared monitor is an optimal choice, which protects user against an arbitrary CCI fault space excluding the ones with the form of ionosphere anomalies, and at the same time, achieves lower probability of missed detection than other monitors with the same fault magnitude. [ABSTRACT FROM AUTHOR]

Objectives Satellite based augmentation system (SBAS) improves the positioning accuracy and integrity by broadcasting ephemeris corrections and associated integrity parameters through geostationary Earth orbit (GEO) satellites. SBAS GEO satellite can also be used as a ranging source together with GPS satellites to improve the system performance. User range error (URE) of the GEO satellite and their effect on positioning results are investigated. URE of SBAS GEO and GPS satellite is determined by weighting the observation residuals which are derived with fixed station coordinates. SBAS messages are applied to correct the orbit and clock errors contained in broadcast ephemeris and the ionosphere delay. Ranging data from GEO satellite is engaged in the SBAS positioning process to explore the impact on positioning accuracy, integrity and availability.Methods SBAS messages broadcast by wide area augmentation system (WAAS), BeiDou SBAS (BDSBAS), GPS aided GEO augmented navigation (GAGAN) and multi-functional satellite augmentation system (MSAS) and real data from international GNSS service (IGS) stations are applied to perform the assessment. European geostationary navigation overlay service (EGNOS) and system for differential corrections and monitoring (SDCM) are not included because of the absence of the ranging capability.Results WAAS GEO satellite has the best performance with ranging accuracy better than 1.6 m. The 99.9% error bound is less than 6.8 m while the broadcast user differential range error (UDRE) for the GEO satellite is 7.5 m, which meets the integrity requirement. The 3 GEO satellites of BDSBAS show ranging biases of 14.32 m, 12.64 m and 17.44 m respectively, and the accuracy is better than 2.9 m. After removing the bias, the related 99.9% error bound is 8.60 m, 7.80 m and 11.60 m which suggests an UDRE of 11-12. User range accuracy (URA) of 15 is broadcast in message type 9 for the BDSBAS GEO satellites. URE of the GAGAN GEO satellite is better than 13.9 m and MSAS is better than 3.2 m. The UDRE of GAGAN and MSAS is 14. URE of GPS satellite after augmented by SBAS is also calculated for comparison purpose. Ranging accuracy of GPS is 0.60 m, 0.53 m, 0.21 m and 0.34 m for WAAS, BDSBAS, GAGAN and MSAS respectively. WAAS GEO satellite is selected to perform the positioning analysis whose UDRE is less than 14 so that it can be weighted properly in the solution. Engagement of GEO satellite in SBAS positioning will lead to lower position dilution of precision (PDOP) and reduce the protection level especially for the blockage circumstance. The system availability of localizer performance with vertical guidance 200 (LPV200) service is improved from 99.984% to 99.997% with collaboration of 3 GEO satellites' observation.Conclusions With sufficient GPS satellites, the combination of GEO satellites will decrease the positioning accuracy because of the relative larger range error, while with less available satellites, combining the GEO satellite data effectively reduces the protection level and improves the system availability. Results suggest that SBAS GEO ranging data should be included in the SBAS solution for aviation users. [ABSTRACT FROM AUTHOR]

This research evaluates the performance of the first and second-generation satellite-based augmentation system (SBAS) GAGAN and BDSBAS services in Thailand. The study initially analyses GNSS observations from 40 local continuously operating reference stations (CORS) over the past 12 months in 2022, providing initial horizontal and vertical accuracies at 2.03 and 3.66 m respectively with the single point positioning (SPP) mode. The positioning accuracies are 2.27 m horizontally and 2.54 m vertically as of GAGAN, while 2.94 m horizontally and 3.90 m vertically as of BDSBAS with the first-generation system. Since the 1st generation SBAS performance is affected by the ionosphere, especially in the equatorial and auroral regions, the ionosphere-free combination is applied in the SPP algorithm as well as the 2nd generation SBAS with the Dual-Frequency Multi-Constellation (DFMC) capable receivers for BDSBAS only. The SPP accuracies are 1.51 m horizontally and 3.26 m vertically, where the BDSBAS results are 2.16 m horizontally and 4.28 m vertically. Demonstrated results show that the positioning accuracy cannot be improved significantly when applying the 1st generation GAGAN and BDSBAS systems and the 2nd generation BDSBAS system in Thailand due to the low number of common satellites available, especially when using the SBAS outside their ground tracking network; therefore, it is expected to apply the GNSS observation and computed satellite error correction from the regional ground tracking network to enhance the performance of the 2nd generation SBAS. The positioning accuracy result could be achieved at sub-metre level, which will greatly benefit high-accuracy applications such as air, land, and sea navigation in the region. [ABSTRACT FROM AUTHOR]

In Jakarta, Indonesia, rapid urbanization and intensive groundwater extraction have led to significant land subsidence, posing challenges for sustainable urban management. This study utilized Interferometry Synthetic Aperture Radar (InSAR) integrated with multi-track data analysis to generate refined time-series and velocities of 2D displacement across Greater Jakarta. This study reveals notable variation in subsidence rates across different areas, with the most significant subsidence observed in Cikarang and the coastal regions of North Jakarta, which remains linear to this day. Notably, while the 2D approach improved accuracy by up to 53% at some locations, discrepancies at others indicated that simpler descending projections might sometimes yield better results. This underscores the necessity for a nuanced application of geodetic methods based on specific site conditions to effectively monitor and manage land subsidence in complex urban environments. Our findings highlight the critical importance of integrating multiple monitoring approaches to comprehensively address both vertical and horizontal displacement. [ABSTRACT FROM AUTHOR]

Ground deformation is one of the crucial issues threatening many cities in both societal and economic aspects. Interferometric synthetic aperture radar (InSAR) has been widely used for deformation monitoring. Recently, there has been an increasing availability of massive archives of SAR images from various satellites or sensors. This paper introduces Multi-Satellite SBAS that exploits complementary information from different SAR data to generate integrated long-term ground displacement time series. The proposed method is employed to create the vertical displacement maps of Almokattam City in Egypt from 2000 to 2020. The experimental results are promising using ERS, ENVISAT ASAR, and Sentinel-1A displacement integration. There is a remarkable deformation in the vertical direction along the west area while the mean deformation velocity is −2.32 mm/year. Cross-validation confirms that the root mean square error (RMSE) did not exceed 2.8 mm/year. In addition, the research findings are comparable to those of the previous research in the study area. Consequently, the proposed integration method has great potential to generate displacement time series based on multi-satellite SAR data; however, it still requires further evaluation using field measurements. [ABSTRACT FROM AUTHOR]

The article shows the results of a study on the determination of SBAS satellite positioning integrity parameters as a HPL and VPL protection levels. To this end, a modified algorithm was developed to determine the HPL and VPL protection levels from a common aircraft position navigation solution based on EGNOS and SDCM augmentation systems. The developed mathematical scheme was verified on real GNSS kinematic data recorded by two onboard Septentrio AsterRx2i and Trimble Alloy receivers installed on a Diamond DA 20-C aircraft. Based on the conducted tests, it was found that the HPL parameter does not exceed 12.24 m, while respectively the VPL does not exceed 18.01 m. In addition, in the course of the study it was found that the proposed EGNOS+SDCM solution improves the HPL/VPL integrity determination in relation to the EGNOS solution by 8÷66%. The mathematical scheme used in the study was also applied to designation the HPL/VPL terms for the UAV platform. The obtained results of the HPL/VPL values for the positioning of the aircraft and the UAV platform show a high efficiency of the developed algorithm for improving the integrity parameter.

This work discusses landslide velocity mapping in the Swiss Alps using ALOS-2 PALSAR-2 ScanSAR differential interferometry and interferometric time series analyses based on small data stacks of about 10 images over eight years. A wide area coverage is possible due to the 350km swath width of the ScanSAR data. In our processing sequence we resampled the sub-swath SLCs to a common spatial grid. The co-registered sub-swath SLCs were mosaiced into large co-registered mosaic SLCs. We then applied normal procedures also used for stripmap mode data to generate differential interferograms and conduct a Persistent Scatterer Interferometry (PSI) processing. The results obtained over the Swiss Alps provide a good spatial coverage, with line-of-sight displacement velocities also extracted for some landslides in forested areas. The future applicability of the technique is very promising with upcoming L-band SAR missions (NISAR, ROSE-L and PALSAR-3) that provide data of even better suitability – higher spatial resolution, shorter revisit time intervals, and free and open data access. [ABSTRACT FROM AUTHOR]

Vertical deformation associated with the displacement of rock glaciers in the upper Mapocho river basin, in the central Andes of Chile, was monitored using a series of PAZ radar satellite images and the DInSAR technique. Forty-one PAZ images of ascending and descending orbit were processed with the Small Baseline Subset (SBAS) technique. Regarding the obtained results, it was estimated that the vertical displacement velocity of rock glaciers between October 9, 2019 and April 22, 2021 reached up to -22 mm/year and the movement in the W-E direction ranged from -47 to 38 mm/year. This remote sensing technique is a useful tool to measure the surface displacement of rock glaciers, compared to conventional techniques such as GNSS point measurements, especially in the semi-arid Andes, which is one of the most important reservoirs of these geoforms worldwide. [ABSTRACT FROM AUTHOR]

Today, the phenomenon of subsidence has affected many regions of the world, including densely populated cities in arid and semi-arid regions, and has caused a lot of damage. The phenomenon of subsidence is imperceptible and gradual, and in the long term it causes a lot of damage to agricultural lands as well as urban areas. Considering the many negative effects that the subsidence phenomenon has on human activities and man-made phenomena including buildings and facilities, not paying attention to it can be associated with many human and financial losses. Based on this, it will be very important to monitor the amount of land subsidence in order to reduce the negative effects and also to control its development process, and it is necessary to regularly estimate the subsidence process of the areas. Due to the fact that the phenomenon of subsidence occurs imperceptibly and its monitoring requires high precision, therefore, new methods should be used to monitor this risk. One of the methods that has received a lot of attention in recent years is the radar interferometry method, which has high accuracy and speed in processing information and monitoring changes in the earth's surface. Accordingly, in this research, this method is used. It will be used to evaluate the subsidence of Asadabad Plain. According to the mentioned cases, in this research, using radar images and radar interferometry method, the state of subsidence and its trend in Asadabad Plain and the analysis of the geomorphological factors affecting its occurrence have been evaluated. [ABSTRACT FROM AUTHOR]

Subsidence induced by groundwater (GW) in the plains of Zanjan and Qazvin provinces in northwestern parts of Iran has impacted various infrastructures. Hence, investigating the study area to identify the risky zones and identifying the vulnerable members of power transmission towers (PTTs) are required by policy-makers. This study investigated the impact of GW depletion on land subsidence and its effect on PTTs in the Zanjan and Qazvin provinces. Subsidence maps were acquired via time series analysis by performing a small baseline subset on Sentinel-1 (2017-02-23 till 2019-02-25) satellite data. Results indicate maxima values of 132 mm/years and 80 mm/years subsidence rates in line-of-sight direction for Qazvin and Zanjan provinces, respectively. Observed GW shows a rapid decline of piezometric head of 13.2 m for Qazvin province. Furthermore, GW head drop, coupled with the dominance of fine-grained soils in Qazvin province, increases the probability of plain-wide subsidence. Employing a finite element method analysis on two commonly utilized PTTs in the region illustrated such vulnerable members (bottom legs and first transverse plane) under support settlement conditions. However, the T-30 tower, by mitigating the stress to more members of the tower, performed superior in most subsidence scenarios. It is recommended to implement new policies such as avoiding risky zones for developing PTTs, installing T-30 towers instead of DC towers in obstructed routes, and continuous monitoring of threatened PTTs. [ABSTRACT FROM AUTHOR]

SBAS systems are applied in precise positioning of UAV. The paper presents the results of studies on the improvement of UAV positioning with the use of the EGNOS+SDCM solutions. In particular, the article focuses on the application of the model of totaling the SBAS positioning accuracy to improve the accuracy of determining the coordinates of UAVs during the realisation of a test flight. The developed algorithm takes into account the position errors determined from the EGNOS and SDCM solutions. as well as the linear coefficients that are used in the linear combination model. The research was based on data from GPS observations and SBAS corrections from the AsteRx-m2 UAS receiver installed on a Tailsitter platform. The tests were conducted in September 2020 in northern Poland. The application of the proposed algorithm that sums up the positioning accuracy of EGNOS and SDCM allowed for the improvement of the accuracy of determining the position of the UAV by 82-87% in comparison to the application of either only EGNOS or SDCM. Apart from that, another important result of the application of the proposed algorithm was the reduction of outlier positioning errors that reduced the accuracy of the positioning of UAV when a single SBAS solution (EGNOS or SDCM) was used. The study also presents the effectiveness of the proposed algorithm in terms of calculating the accuracy of EGNOS+SDCM positioning for the weighted average model. The developed algorithm may be used in research conducted on other SBAS supporting systems. [ABSTRACT FROM AUTHOR]

The tectonic positioning of Iran has led to significant seismic activity in the region, particularly in the Alborz Unit. This study focused on investigating the morphotectonic status of Lavasan Sub-basins located on the southern slopes of the Alborz. To achieve this, a digital elevation model with 30-meter resolution, a 1:50,000 topographic map, a 1:100,000 geological map, and Sentinel-1 radar images were utilized as research data. The analysis employed GMT, ArcGIS, and SPSS software, along with specific indicators to assess the tectonic condition of the region. The research was conducted in two stages. Firstly, the tectonic conditions of the sub-basins were evaluated using morphotectonic indicators and secondly, the vertical displacement of the region was assessed using radar images and the SBAS time-series method. The results of the study indicated that Lavasan Sub-basins exhibited high tectonic activities with Barg and Kond basins averaging a score of 1.88 and Lavasan and Afjeh basins averaging a score of 2. Consequently, the latter basins demonstrated a more active tectonic status based on the IAT index. Additionally, the results obtained from the SBAS time-series method over a 3-year period (from 01/06/2016 to 12/21/2018) revealed a 79-mm elevation and a 14-mm depression, which could be attributed to tectonic activity, thus corroborating the accuracy of the results obtained from morphotectonic indicators. [ABSTRACT FROM AUTHOR]

Interferometry synthetic aperture radar (InSAR) technology has emerged as a powerful tool for the early identification and monitoring of geological hazards in the Loess Plateau. Since the SAR satellite adopts the range-azimuth two-dimensional side-looking imaging mode, the corresponding field area of the pixel will change with slope, aspect, and incident angle, especially in areas with severe changes in terrain and landforms, which causes serious area distortion, leading to abnormal deformation rate mapping. Considering the SAR imaging geometry, terrain slope and aspect conditions, this article proposes a quantitative analysis method for accurate geometric distortion (GD) based on pixel area and corresponding field area and constructs a weighted fusion method based on distortion values for InSAR deformation rate maps in overlapping regions of adjacent tracks. Taking Lingtai County, Gansu Province as the research area and sentinel-1 data as the research data, we utilize the SBAS method to process the sentinel-1 data and estimate the deformation rate, and then use the GD value as a weight factor to estimate the fusion rate of the overlapping area of adjacent tracks. The results demonstrate that the weighted fusion method based on distortion values can achieve a high-quality mosaic effect of deformation rate maps of adjacent tracks, effectively improve the GD influence in deformation rate mapping, and the identification of geological hazards.

In this study, Differential Interferometric Synthetic Aperture Radar Interferometry (DInSAR) of artificial Corner Reflectors (CRs) were validated in the area of fast and nonlinear deformation gradient caused by active coal longwall exploitation. Three Sentinel-1 datasets were processed using conventional DInSAR, Persistent Scatterer Interferometry (PSI), and Small BAseline Subset methods implemented in ENVI SARscape™. For evaluation, leveling and Global Navigation Satellite System (GNSS) measurements were used. Considering the challenge of snow cover, the removal of all winter images was not a successful strategy due to the long temporal baseline and strong movement, which cause phase unwrapping problems and underestimate the real deformation. The results indicate that only conventional DInSAR and SBAS with low network redundancy allow us to capture maximal deformation gradient and the root mean square error calculated between the CRs and the ground truth is on the level of 2–3 cm for the vertical and easting deformation component, respectively. For the small deformation gradient represented by the permanent GNSS station (4 cm/year), all SBAS techniques appeared to be more accurate than DInSAR, which corresponds to higher redundancy and better removal of the atmospheric signal. In contrast, DInSAR results allowed to capture information about two subsidence basins, which was not possible with SBAS and PSI approaches.

Landslides pose significant threats to life and property, particularly in mountainous regions. To address this, this study develops a landslide susceptibility model integrating Earth Observation (EO) data, historical data, and Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) ground movement results. The model categorizes areas into four susceptibility classes (from Class 1 to Class 4) using a multi-class classification approach. Results indicate that the Xtreme Gradient Boosting (XGB) model effectively predicts landslide susceptibility with area under the curve (AUC) values ranging from 0.93 to 0.97, with high accuracy of 0.89 and a balanced performance across different susceptibility classes. The integration of MT-InSAR data enhances the model’s ability to capture dynamic ground movement and improves landslide mapping. The landslide susceptibility map generated by the XGB model indicates high susceptibility along the Pacific coast. The optimal model was validated against 272 historical landslide occurrences, with predictions distributed as follows: 68 occurrences (25%) in Class 1, 142 occurrences (52%) in Class 2, 58 occurrences (21.5%) in Class 3, and 4 occurrences (1.5%) in Class 4. This study highlights the importance of considering temporal changes in environmental conditions such as precipitation, distance to streams, and changes in vegetation for accurate landslide susceptibility assessment.

SBAS is mainly used in civil aviation and navigation, and will be applied to autonomous driving in the future. Given the open signal format of the Satellite Based Augmentation System (SBAS), which exposes security threats such as spoofing attacks, the utilization of SBAS navigation message authentication technology can improve the SBAS anti-spoofing ability from the system side. SBAS message authentication technology has become the future direction of SBAS system development. However, during the initial design of SBAS on L1, message authentication technology was not considered, and the addition of authentication messages will lead to further strain on existing message bandwidth resources. Therefore, in response to the issue of insufficient bandwidth resources after adding authentication messages to SBAS L1, a study on message scheduler for SBAS L1 authentication was conducted. A fixed time sequence dynamic message scheduler for incorporating authentication messages was proposed. This scheduler reduces the frequency of broadcasting clock error parameters to mitigate the impact of adding authentication messages. Furthermore, an optimized fixed time sequence dynamic message scheduler based on SBAS clock error messages was introduced. The results show that the message scheduler can not only improve the flexibility of SBAS message broadcasting, but also shorten the update interval of various types of messages under the premise of meeting the maximum update interval requirement. With minimal impact on the maximum message update interval, it improves the integrity, authenticity, and availability of messages. This approach can increase the effective message ratio in SBAS to over 91%, and the optimal solution reduces the initial user positioning time to 26 s. [ABSTRACT FROM AUTHOR]

Nowadays, the risk of subsidence as a natural risk has covered many cities, including Izeh city. Considering that subsidence is associated with many negative effects for residential areas, in this research, the amount of subsidence in the Izeh Plain and the analysis of factors influencing its occurrence have been evaluated. In this research, Landsat satellite images, Sentinel 1 radar images, SRTM 30 meters high digital model and library information were used as research data. The most important research tools are ArcGIS, ENVI, IDRISI and GMT. The models used in the research included maximum likelihood model, LCM model and SBAS model. This research has been done in two general stages, in the first stage, the subsidence of the region was evaluated using the SBAS time series method, and in the second stage, using Landsat satellite images, the development process of man-made uses and areas A settlement has been evaluated. According to the results, the city of Izeh has subsided between 13 and 68 mm during a period of 2 years (from 2020/10/01 to 2022/15/01), the highest amount of which is related to the southern and southern regions. It was east of this city. Also, the results of this research have shown that the residential and man-made urban areas and urban outskirts of Izeh have encountered an increase of 7.2 square kilometers during the years 1992 to 2022, and considering that the highest amount of subsidence is also related to this has been areas. Also, based on the studies conducted in Izeh Plain, this plain is faced with the annual discharge of 14.8 Million Cubic Meters of underground water. The total results have shown that human factors, the development of man-made uses and the decline of underground water resources have caused the city of Izeh, especially its southern and southeastern regions, to be at risk of subsidence. [ABSTRACT FROM AUTHOR]

The subsidence is one of the hazards that has posed a significant threat to many plains in the country in recent years. Asadabad Plain in Hamedan province is among those plains with a high potential for subsidence due to its hydro climatic conditions and geomorphology. Because of the importance of this issue, in this research the subsidence status of Asadabad Plain has been assessed and unlike many previous researches, the role of human factors in its occurrence has been analyzed. To do so, Sentinel-1 radar images, Landsat 5 and 8 satellite images, statistical information related to piezo metric wells in the region, and digital elevation layers were used as the primary data sources. Using the SBAS time series method, a subsidence map of the area from 2015 to 2022 was generated, followed by an analysis of the impact of groundwater depletion and land-use changes on subsidence. The results indicate subsidence ranging from 132 to 704 millimeters in Asadabad Plain during 2015 to 2022, with the highest subsidence occurring in the central regions of the plain. Considering the significant correlation (a correlation coefficient of 0.709) between subsidence and groundwater level decline, it can be concluded that one of the main causes of subsidence in Asadabad Plain is the depletion of groundwater resources. The assessment of land-use changes also reveals an increasing trend in agricultural land and human-built areas, corresponding to increased exploitation of groundwater resources and intensified land surface pressure, leading to exacerbated subsidence. Given the persistence of subsidence in this plain, remote sensing monitoring and the establishment of fixed GPS measurement stations facilitate monitoring the rate and extent of subsidence. [ABSTRACT FROM AUTHOR]

Since the first receiver independent exchange format (RINEX) version was released in 1989, it has gone through several versions, making the existing software, such as TEQC, incompatible with certain later versions. This study proposes a new Python package named PyRINEX, which is developed to batch process the most generally used versions of RINEX files, namely 2.0 and 3.0. The proposed package can be used to manage and edit numerous RINEX files as well as perform a data quality check function. PyRINEX can be easily imported into any Python IDE similar to any other open-source Python package, it also makes secondary development easy for users. [ABSTRACT FROM AUTHOR]

The article shows the results of a study on the determination of SBAS satellite positioning integrity parameters as a HPL and VPL protection levels. To this end, a modified algorithm was developed to determine the HPL and VPL protection levels from a common aircraft position navigation solution based on EGNOS and SDCM augmentation systems. The developed mathematical scheme was verified on real GNSS kinematic data recorded by two onboard Septentrio AsterRx2i and Trimble Alloy receivers installed on a Diamond DA 20-C aircraft. Based on the conducted tests, it was found that the HPL parameter does not exceed 12.24 m, while respectively the VPL does not exceed 18.01 m. In addition, in the course of the study it was found that the proposed EGNOS+SDCM solution improves the HPL/VPL integrity determination in relation to the EGNOS solution by 8÷66%. The mathematical scheme used in the study was also applied to designation the HPL/VPL terms for the UAV platform. The obtained results of the HPL/VPL values for the positioning of the aircraft and the UAV platform show a high efficiency of the developed algorithm for improving the integrity parameter. [ABSTRACT FROM AUTHOR]

InSAR capabilities allow us to understand ground deformations in large metropolitan areas, this is key to assessing site conditions in areas in an inherently expanding context. The multi-temporal interferometry of SAR data records ground surface displacement velocities over large metropolitan areas, identifying anomalous and potential geological hazards. The metropolitan city of Concepción, Chile, is an alluvial basin in one of the world's most seismically active subduction zones, where many subduction earthquakes have occurred throughout history. In this study, we monitored the deformations of the ground surface in the metropolitan area of Concepción using two interferometric techniques, the first being Persistent Scatterer Interferometry (PSI) and the second, the Small Baseline Subset (SBAS) technique. To do this, we have used the same Sentinel-1 dataset, obtaining ground movement rates between 2019 and 2021. The velocities were aligned with the GNSS station available in the area. Ground deformation patterns show local deformations depending on factors such as soil type and heterogeneity, and regional deformations due to geographical location in the subduction area. Our results highlight the similarity of the deformation rates obtained with different processing techniques and have also allowed us to identify areas of deformation and compare them to site conditions. These results are essential to evaluate ground conditions and contribute to urban planning and risk management in highly seismic areas. [ABSTRACT FROM AUTHOR]

The frequent geohazards happened in Dadu River basin has greatly threatened the safety of the infrastructure construction and hydropower stations, thus it is of great significance to obtain a geohazard map of Dadu River for the disaster prevention and mitigation. The ascending Sentinel-1A dataset acquired by 2017—2021 were collected to conduct deformation monitoring for regions from Danba to Leshan Section along the Dadu River, based on time series InSAR technique. And through the analysis of InSAR deformation results and optical images, the hidden landslide pots were detected along the Dadu River. The results show that the maximum deformation rate region has reached - 65. 2 mm/ year. Most of the deforming regions are located in the Danba, Shimian and Hanyuan, which are closely related to the geological activity and climate. With the consideration of deformation rate, topography, vegetation cover and deformation areas, totally 15 obvious landslide regions have been identified. InSAR deformation results in the typical region has shown well agreement with the geodetical measurements, which can prove the effectiveness of InSAR large-scale landslide monitoring in the complex regions of Southwestern China. The deformation results in this work will provide important guidance for geohazard control and prevention for the local government. [ABSTRACT FROM AUTHOR]

Satellite-Based Augmentation Systems (SBASs) are designed to enhance the performance of Global Navigation Satellite Systems (GNSSs) for civil aviation users. As SBAS Geostationary Earth Orbit (GEO) satellite signals are received in a wide area, far more non-aeronautical GNSS users utilize SBAS to improve navigation performance. Since ionospheric delay is the principal error source of GNSS and a leading correction aspect of SBAS, the GEO-broadcast ionospheric data quality of six SBASs over the past three years is assessed in this article. Results show that European Geostationary Navigation Overlay Service (EGNOS), System for Differential Correction and Monitoring (SDCM), and Wide-Area Augmentation System (WAAS) have the highest Grid Ionospheric Vertical Delay (GIVD) accuracy judged by the residual Standard Deviation (STD), then followed by BeiDou SBAS (BDSBAS) and Multi-functional Satellite Augmentation System (MSAS), while GPS-Aided GEO Augmented Navigation (GAGAN) is the worst. The 6 m Grid Ionospheric Vertical Error (GIVE) availability is over 90 percent of the time for most Ionospheric Grid Points (IGPs) of all tested SBASs. However, GAGAN and WAAS have a significant availability decline at 3 m GIVE. In addition, the integrity limits of MSAS and WAAS are fairly conservative. In contrast, the confidence bounds of BDSBAS and SDCM are excessively radical that fail to meet the integrity requirement. To improve the ionospheric data quality received from SBAS, a Multi-Layer Perceptron (MLP)-based user-applicable GIVD calibration method is proposed in the article. A well-trained MLP learned temporal and spatial correlations of the IGP delays and extracted transfer functions between broadcast and reference GIVDs to eliminate error. The SBAS processing errors in Differential Code Bias (DCB) compensation, GIVD estimation modeling, and GEO message quantization are rectified by the MLP trained by abundant historical data with Center for Orbit Determination in Europe (CODE) final Global Ionospheric Maps (GIMs) as reference. Test results on real-time data show that over 85 percent IGPs have STD decline after calibration. The STD declination rates of six SBASs except for SDCM are over 15 percent, and the Mean Absolute Error (MAE) and Root Mean Square Error (RMS) calibration effects are dramatic for all systems. Finally, the average GIVEs are reduced by more than 50 percent for EGNOS, GAGAN, MSAS, and WAAS with a 99.9 percent integrity level maintained. Despite no promotion on availability for BDSBAS and SDCM, the proposed method compensates for the integrity issues of the systems. [ABSTRACT FROM AUTHOR]

From the beginning of World War II, dual-axis tracking radars have played an important role in the tracking of missiles in test ranges. These radars operate mostly in S- or C-band of frequencies. However, these Radars have associated problems with the costly maintenance budget, various errors that creep into the data, and inter-radar bias correction. The modern-day global navigation satellite system (GNSS) together with space-based augmentation systems (SBAS) have provided scope to obtain internally generated and telemetered trajectory data from the missile under test (MUT) from the onboard GNSS receiver with SBAS capabilities within comparable or better accuracies. This research presents a comparison of the precession parameters of the MUT's position solutions between data from several tracking radars and those from the enhanced GNSS data. Also, experiments have been conducted using various satellite navigation constellations including NavIC and SBAS augmentation to demonstrate the improvement in accuracy and precession parameters applicable to the Indian scenario. To compete with the outcomes of contemporary satellite-based navigation system together with the augmentation systems for trajectory generation of cooperative missile targets, radar manufacturers must reconsider their design philosophies for usage on missile test ranges. [ABSTRACT FROM AUTHOR]

Urban land subsidence is one of the important limiting factors for urban development, and strengthening the monitoring of urban surface subsidence contributes to long-term urban planning and construction needs. As a subcentral city in the Yangtze River Delta region of China, it is particularly important for Heifei to enhance the monitoring of surface subsidence. In this study, the persistent scatterer interferometric synthetic aperture radar (PS-InSAR) and small baseline subset (SBAS) techniques were used to process 139 scenes of Sentinel-1A SAR satellite ascending orbit data covering the central urban area of Hefei from July 2015 to July 2020, obtaining subsidence information for the region. The results show that the overall urban area of Heifei is relatively stable, but there are certain deformation trends in local areas. Four regions with obvious deformation were selected for the in-depth analysis of their deformation time series. The experimental study in this paper demonstrates that the PS-InSAR and SBAS techniques can achieve the accurate monitoring of large-scale ground subsidence in urban areas, ensuring the safety of buildings and their surrounding environments, and providing information support for urban security maintenance monitoring. [ABSTRACT FROM AUTHOR]

The Great Wall of China constitutes a significant cultural treasure of the Chinese nation and a valuable piece of heritage of world civilization. Owing to both natural and anthropogenic factors, the Great Wall is undergoing gradual deformation, thereby posing considerable challenges to the overall preservation of the associated sites. This study aims to investigate techniques for monitoring deformation at large-scale linear heritage sites, leveraging the Great Wall as a representative example, and to offer valuable insights for monitoring surface deformations at extensive cultural heritage sites worldwide. Employing SBAS-InSAR technology, this research analyzes and monitors the deformation of the Great Wall. A series of Sentinel-1A images captured between March 2017 and January 2022, consisting of 161 scenes, were subjected to SBAS-InSAR processing to derive the deformation rate field along the wall. To ensure the reliability of the findings, a representative mountainous segment, spanning approximately 896.53 km within the scenic corridor of the Great Wall, was selected for analysis. The outcomes indicate that 75.8% of the scenic corridor in Shanxi Province, representing the Ming Great Wall, exhibits relative stability with deformation rates ranging from −10 to 10 mm/year. Conversely, 24.2% of the scenic corridor demonstrates significant deformation, with a maximum subsidence rate of 33.1 mm/year and a maximum subsidence of 148.6 mm. Therefore, this research highlights the potential application of SBAS-InSAR technology in the monitoring and assessment of surface deformation at massive linear cultural heritage sites and offers a reference point for similar monitoring efforts on a global scale. [ABSTRACT FROM AUTHOR]

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Low-altitude photogrammetric studies are often applied in detection of aviation obstacles. The low altitude of the Unmanned Aerial Vehicle (UAV) flight guarantees high spatial resolution (X, Y) of the obtained data. At the same time, due to high temporal resolution, UAVs have become an appropriate tool for gathering data about such obstacles. In order to ensure the required accuracy of orientation of the photogrammetric block, Ground Control Points (GCPs) are measured. The recently introduced UAV positioning solutions that are based on Post-Processing Kinematic (PPK) and Real Time Kinematic (RTK) are known to effectively reduce, or, according to other sources, even completely eliminate the necessity to conduct GCP measurements. However, the RTK method involves multiple limitations that result from the need to ensure continuous communication between the reference station and the rover receiver. The main challenge lies in achieving accurate orientation of the block without the need to conduct time-consuming ground measurements that are connected to signalling and measuring the GCPs. Such solution is required if the SPP code method is applied to designation the position of the UAV. The paper presents a research experiment aimed at improving the accuracy of the determination of the coordinates of UAV for the SPP method, in real time. The algorithm of the SPP method was improved with the use of IGS products.

Here we delineate a complete satellite-based augmentation system (SBAS) authentication scheme, including over-the-air rekeying (OTAR), that uses the elliptic curve digital signature algorithm (ECDSA) and timed efficient stream loss-tolerant authentication (TESLA) without the quadrature (Q) channel. This scheme appends two new message types to the SBAS scheduler without overburdening the message schedule. We have taken special care to ensure that our scheme (1) meets the appropriate security requirements needed to prevent and deter spoofing; (2) is compatible with existing cryptographic standards; (3) is flexible, expandable, and future-proof to different cryptographic and implementation schemes; and (4) is backward compatible with legacy receivers. The scheme accommodates a diverse set of features, including authenticating core-constellation ephemerides. We discuss the SBAS provider and receiver machine state and its startup, including its use by aircraft that traverse differing SBAS coverage areas. We tested our scheme with existing SBAS simulation and analysis tools and found that it had negligible effects on current SBAS availability and continuity requirements. [ABSTRACT FROM AUTHOR]

According to aviation minimum operational performance standards (MOPS), protection levels for satellite-based augmentation systems (SBASs) are to be computed as the product of the estimated standard deviation of errors and a scaling, or K-factor. MOPS recognized that K-factors were originally chosen to be consistent with certain assumptions that may not hold under all conditions. Considering the limited applicability of aviation-based K-factors, it will be important to identify a more rigorous method for deriving new SBAS applications for road, rail, or maritime use. Here we describe an innovative method applicable to any integrity risk (e.g., at 10-7 for aviation or 10-5 for maritime applications) and time interval T (e.g., 150 seconds to 1 hour for aviation or 3 hours for maritime use). This new method relies on rigorous probability justification. No restrictive assumptions are needed for the time correlation pattern of the errors. The method is easy-to-implement and applicable to any type of integrity risk or time interval T. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Geodesy & Geodynamics (1671-5942) is the property of Editorial Board Journal of Geodesy & Geodynamics 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.)

Jiaozuo, located in the northwest of Henan Province, is one of the six major anthracite production bases in China. It is susceptible to land subsidence due to over a hundred years of mining history, continuous urbanization, frequent human activities, etc., which poses a great threat to urban infrastructure construction and people's production and lives. However, traditional leveling techniques are not sufficient for monitoring large areas of land subsidence due to the time-consuming, labor-intensive, and expensive nature of the process. Furthermore, the results of conventional methods may not be timely, rendering them ineffective for monitoring purposes. With the continuous advancement of urbanization, land subsidence caused by groundwater extraction, ground load, and other factors in daily life poses a great threat to urban infrastructure construction and people's production and lives. In order to monitor the land subsidence in the area of Jiaozuo city, this article uses the Sentienl-1A satellite data covering the city from March 2017 to March 2021 to obtain the accumulated land subsidence and the average land subsidence rate based on the Small Baselines Subset InSAR (SBAS-InSAR) technology. The results indicate that the surface of Jiaozuo area is generally stable, and there has been no large-scale settlement. The settlement rate is roughly between −1 mm/a and 2.2 mm/a, and the areas with obvious land subsidence are mainly located in the southeast and east of Jiaozuo city center. After field investigation, it was found that the land subsidence is mainly caused by two reasons: groundwater excessive mining and excessive surface load. In the northeast of Jiaozuo city, there is a certain uplift area. After on-site investigation, it was found that the area is connected to a tailings pond of an aluminum mine, constantly accumulating abandoned rock masses and sediment, causing an annual uplift rate of +6~+ 24 mm/a. The large-scale extraction of groundwater from farmland in the urban–rural integration area for irrigation of wheat has led to the settlement of buildings in the area with a rate of −11–−74 mm/a. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study on the use of different tropospheric correction models in SBAS positioning for air navigation. The paper, in particular, determines the influence of the Saastamoinen troposphere and RTCA-MOPS models on the determination of aircraft coordinates and mean coordinate errors in the SBAS positioning method. The study uses real kinematic data from a GPS navigation system recorded by an onboard GNSS satellite receiver as well as SBAS corrections. In the experiment, the authors include SBAS corrections from EGNOS and SDCM augmentation systems. The navigation calculations were performed using RTKLIB v.2.4.3 and Scilab 6.1.1 software. Based on the conducted research, it was found that the difference in aircraft coordinates using different troposphere models can reach up to ±2.14 m. Furthermore, the use of the RTCA-MOPS troposphere model improved the values of mean coordinate errors from 5 to 9% for the GPS+EGNOS solution and from 7 to 12% for the GPS+SDCM solution, respectively. The obtained computational findings confirm the validity of using the RTCA-MOPS troposphere model for SBAS positioning in aerial navigation.

Ground deformation is one of the crucial issues threatening many cities in both societal and economic aspects. Interferometric synthetic aperture radar (InSAR) has been widely used for deformation monitoring. Recently, there has been an increasing availability of massive archives of SAR images from various satellites or sensors. This paper introduces Multi-Satellite SBAS that exploits complementary information from different SAR data to generate integrated long-term ground displacement time series. The proposed method is employed to create the vertical displacement maps of Almokattam City in Egypt from 2000 to 2020. The experimental results are promising using ERS, ENVISAT ASAR, and Sentinel-1A displacement integration. There is a remarkable deformation in the vertical direction along the west area while the mean deformation velocity is −2.32 mm/year. Cross-validation confirms that the root mean square error (RMSE) did not exceed 2.8 mm/year. In addition, the research findings are comparable to those of the previous research in the study area. Consequently, the proposed integration method has great potential to generate displacement time series based on multi-satellite SAR data; however, it still requires further evaluation using field measurements.

• A method for extending polarimetric optimization of PS-InSAR and SBAS techniques on dual polarized Sentinel-1 data is proposed. • The phase quality and density of coherent pixels in both techniques are improved with the proposed method. • The potentials of the proposed method for differential land covers are investigated. The rationale of combining polarimetric SAR data with multi-temporal InSAR techniques, which is based on polarimetric optimization, is to improve their performance in identifying coherent pixels and increasing the accuracy of deformation monitoring. This paper extended the polarimetric optimization of Persistent Scatterer Interferometry (PSI) and Small Baseline Subset (SBAS) techniques on dual-polarized Sentinel-1 data. For this purpose, 20 dual-polarization (VV/VH) SAR images acquired by the Sentinel-1A sensor were used. The results indicated that by applying polarimetric optimization on dual-polarized data in the SBAS technique, the number of candidate and final coherent pixels increased 2.95 and 1.42 times, respectively. Similarly, the number of candidate and final coherent pixels (CP) increased 3.12 and 1.45 times in the PSI technique, respectively. Also, the effect of the polarimetric optimization on increasing the density of coherent points in different regions was investigated. In this framework, Sentinel-2 time-series images were classified into four classes (bare soil, vegetation, build-up, and others) using Google Earth Engine by applying remote sensing indices. This demonstrated that polarimetric optimization of the SBAS technique was more effective in bare soil and vegetated regions than in urban areas. However, polarimetric optimization of the PSI technique was more successful in non-urban regions than in urban areas. An external comparative analysis was also performed between the deformation results derived by PSI and SBAS techniques and GPS observation. The evaluation demonstrated that polarimetric optimization coupled with multi-temporal InSAR analysis yielded more reliable deformation results than conventional single-polarimetric data. [ABSTRACT FROM AUTHOR]

This work demonstrates the potential of synthetic aperture radar interferometry (InSAR) based on interferometric point target analysis (IPTA) approach for landslide-induced deformation measurement. Twenty-eight Sentinel-1A images acquired between October 14, 2014, and October 27, 2016, are employed in order to measure the surface deformation associated with Kahroud landslide, northern Iran. Due to the lack of geodetic measurements and thanks to capability of processing small baseline highly coherent interferograms in the study area, the conventional small baseline subset (SBAS) time series analysis is exploited for investigation of the IPTA performance. The cross-comparison indicates some unwrapping errors in the IPTA results and removal of a large number of point target candidates due to the remained nuisance terms in the phase measurements, the deviation of the deformation behavior from a simple linear model employed by IPTA and the temporal gap in the available dataset. Two different sliding mechanisms, however, are revealed based on the SBAS time series analysis results. In the second part of the research, the slope stability analysis to characterize the slope dynamics is finally performed based on the deformation field extracted from two ascending and descending single interferograms. Accordingly, the soil shear strength parameters as well as a 3D model of the sliding surface are estimated followed by the calculation of the soil mass involved by the Kahroud landslide. [ABSTRACT FROM AUTHOR]

A strong earthquake of Mw 7.3 hit the border region between Iran and Iraq on November 12, 2017. Several InSAR-based coseismic inversion studies suggested that the earthquake occurred on a northeast dipping Mountain Front Fault within the Precambrian Arabian basement. In this study, we use multiple ascending and descending pass C-band Sentinel-1 images to study the earthquake's pre- and post-seismic surface displacements. We performed SBAS time series from June 2017 to March 2018 to understand the spatiotemporal evolution of the displacement before and after the November event. The pre-seismic time series displacement values range as high as –89 mm in descending pass and –96 mm in ascending pass. The pre-seismic time series analysis reveals subsidence between 84 and 0 days before the earthquake, which might be due to excessive groundwater pumping. The post-seismic displacements showed logarithmic decay, indicating afterslip. Even though the earthquake occurred on a blind reverse fault, we highlight that the post-seismic afterslip is composed of horizontal and vertical deformation components, which can be inferred from the variation in the displacement values of the descending and ascending passes. We believe that the small magnitude earthquakes and the January 2018 Mandali earthquake sequence in the Zagros Mountain region affect the spatiotemporal evolution of the November event afterslip. Research Highlights: The temporal evolution of the pre-seismic displacement indicates significant ground subsidence before the earthquake. The pre-seismic ground subsidence due to excessive groundwater withdrawal combined with the interseismic strain accumulation might result in a reverse faulting earthquake. The results highlight the importance of the multi-temporal InSAR technique in the field of earthquake precursory studies. Several small magnitude earthquakes and the Mandali earthquake sequence that occurred after the earthquake affected the temporal evolution of the post-seismic afterslip. The pre-seismic deformation is dominantly vertical, whereas the post-seismic deformation is a combination of horizontal and vertical motion. [ABSTRACT FROM AUTHOR]

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Copyright of Mountain Research (10082786) is the property of Mountain Research Editorial Office 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.)

مخاطره فرونشست در طی سال­های اخیر، شهرهای زیادی ازجمله شهرهای مناطق خشک و نیمه­خشک ایران را با چالش جدی مواجه کرده است. شهر همدان ازجمله شهرهایی است که در معرض این مخاطره قرار دارد و به همین دلیل در این پژوهش به ارزیابی میزان فرونشست در محدوده این شهر پرداخته شده است. داده­های مورد استفاده در این تحقیق شامل تصاویر راداری سنتینل 1، تصاویر ماهواره لندست، مدل رقومی ارتفاعی 30 متر SRTM و اطلاعات مربوط به منابع آب زیرزمینی بوده است. ابزارهای مهم نیز تحقیق شامل ArcGIS، GMT و ENVI بوده است. این تحقیق به‌طورکلی در سه مرحله انجام شده است که در مرحله اول، نقشه­های کاربری اراضی منطقه مربوط به سال­های 1991 و 2020، تهیه و تحلیل شده است. در مرحله دوم وضعیت افت منابع آب زیرزمینی در محدوده مطالعاتی بررسی شده است و در مرحله سوم نیز با استفاده از تصاویر راداری و روش سری زمانی SBAS، میزان فرونشست منطقه در طی دوره زمانی سه‌ساله (2017 تا 2020) محاسبه شده است. بر اساس نتایج به دست آمده، محدوده شهری و حاشیه شهری همدان سالانه با حدود 1 متر افت منابع آب و 7/. کیلومترمربع توسعه فیزیکی مواجه شده است. همچنین میزان فرونشست این محدوده در طی دوره زمانی سه‌ساله، بین 6 تا 98 میلی­متر بوده است که مطابق نقشه نهایی تهیه شده، مناطق غربی شهر همدان بین 60 تا 98 میلی­متر، مناطق مرکزی بین 30 تا 60 میلی­متر و بخش زیادی از مناطق شرقی آن بین 6 تا 30 میلی­متر فرونشست داشته است. با توجه به اینکه بیش­ترین میزان توسعه فیزیکی شهر همدان در طی سال­های اخیر، در مناطق غربی و حاشیه­ای این شهر بوده است؛ می­توان گفت که توسعه فیزیکی شهر همدان به‌موازات افت منابع آب زیرزمینی، عامل اصلی این فرونشست بوده است.

Currently operating satellite-based augmentation systems (SBASs) provide an augmentation service that improves global positioning system (GPS) performance at 250 bps via the L1 signal. Despite their efficiency, existing SBASs cannot support other global navigation satellite systems (GNSSs) owing to their narrow bandwidth, which prevents us from taking advantage of multi-constellation GNSS positioning. This paper proposes the concept of single-frequency multi-constellation (SFMC) SBAS, which enables the L1 legacy SBAS to support up to four or five constellations with minimal changes to existing standards and systems. Since upgrading existing SBAS avionics and changing international standards are not trivial tasks, we propose the SFMC SBAS messages that offer backward compatibility with legacy SBAS users. The transmission of fast corrections along with long-term corrections in message type (MT) 25 allows us to reserve the bandwidth for providing multi-constellation messages by removing MT 2 to 5, while modified MT 6 does not let the service compromise the timely alert requirements. Performance evaluations using the actual broadcast SBAS messages and observation data from GNSS reference stations show that the proposed SFMC SBAS reduces the maximum error of the legacy SBAS by 25% to 40% and enables Wide-Area Augmentation System (WAAS) to meet high integrity trucking user requirements anywhere in the continental United States (CONUS). Thus, SFMC SBAS is expected to not only improve the navigation performance of existing SBASs practically and effectively but also contribute to the improvements of accuracy and integrity performance. Specifically, we suggest the SFMC SBAS messages that are designed to be compatible with both L1 legacy and upgraded SBAS equipment, allowing for a smooth transition to the new technology.