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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]

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]

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]

• 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]

• The segment method in the SBAS processing. • A novel thermokarst landslides susceptibility (TLS) model integrated improved SBAS method and machine learning. • Influence factors and distribution features of TLS. Thermokarst landslides (TLs), which are made up of retrogressive thaw slumps (RTSs) and active-layer detachments slides (ALDSs), are quickly increasing in the central Qinghai-Tibet Plateau (QTP) permafrost area. TLs induce many environmental problems and threaten the safety of infrastructure. A landslide susceptibility map is crucial to prevent the negative impacts of these landslides. However, traditional thermokarst landslides susceptibility (TLS) evaluations do not consider real-time surface deformation information. Therefore, we propose a novel method that integrates a conventional machine learning model with ground surface deformation. Nine influencing factors, including slope, normalized difference vegetation index, elevation, precipitation, thawing degree days, soil content, active layer thickness, water content, and vegetation type were selected based on the q-index detector, and support vector machine was employed to obtain an initial model (IM). We obtained surface deformation in the study area using the enhanced Small Baseline Subset (SBAS) method. The accuracy of the InSAR results was validated through comparison with data from two field monitoring cross-sections. Subsequently, we established an integrated model (ITM) by combining the initial model with surface deformation using the contribution matrix, and confirmed the fusion model's higher rationality and accuracy through comparison with the IM. Furthermore, we examined the impact of the quadtree segmentation method on atmospheric correction and validated the TLS results obtained using the ITM with high-resolution optical remote sensing imagery from GF6. Finally, the influencing factors and distribution characteristics of TLS was analyzed, and the results indicated that climatic conditions are the primary factors affecting the distribution of TLS. [ABSTRACT FROM AUTHOR]

Detecting and monitoring surface deformation using radar satellite data is vital in geohazard assessment. Sentinel-1 has provided unprecedented spatial and temporal resolution, but data processing is complicated and poses computational challenges. Although software and tools exist, each with its own limitations. SNAP-ESA is notable for its user-friendly interface and stable performance in Interferometric Synthetic Aperture Radar (InSAR). However, SNAP-ESA lacks a flexible approach for generating interferometric time series stacks for Persistent Scatterer Interferometry (PSI) and Small Baseline Subset (SBAS) techniques and faces computational challenges over large areas. Here, we present an automated Python workflow, SNAPWF, using SNAP-ESA to enable efficient PSI and SBAS interferometric time series stacks generation using flexible network graphs. SNAPWF has been implemented on a dedicated geospatial computing platform, enabling efficient performance over large areas. Results confirm its ability to generate PSI and SBAS interferometric stacks using full Sentinel-1 scenes and achieve results comparable to existing software. • This study introduces a Python workflow on the Geospatial Computing Platform (GCP) for generating PSI and SBAS stacks. • Parallelization on GCP enhances workflow performance and reduces computing time for PSI and SBAS interferograms. • The workflow tests show promising results compared to other tools and services. [ABSTRACT FROM AUTHOR]

Diverse studies about equatorial plasma bubble structures and their relation with ionospheric scintillation have been performed in the last decades. Among many findings, the investigations usually reported dominant plasma bubble eastward velocity with a magnitude of few tens of m/s and larger amplitude scintillation for transionospheric signals aligned with these depleted structures. However, an uncommon long-lasting event with negligible average zonal drift prevailing for hundreds of minutes was registered over the Brazilian region, allowing a case study of the scintillation pattern under this particular condition. Data from ionosondes, all-sky imager (6300 Å filter), geostationary satellites and Global Navigation Satellite System were used here, covering the eastern portion of the Brazilian ionosphere. The results show that the scintillation was less intense than in other nights around the event, suggesting that larger plasma density gradients and sequential bubble structures seem to cause more severe scintillation scenario than the alignment condition alone, even though the last also contributes to worsen the scintillation effects. Regarding the stagnant bubble pattern, the results suggest prevailing E region Hall conductivity and equatorward wind as potential agents. [ABSTRACT FROM AUTHOR]

This work discusses InSAR time series analysis using multi-reference stacks with exclusively short time intervals. A 5 months long stack of Sentinel-1 acquisitions over a high alpine territory that includes fast moving landslides is used. Use of the multi-look phases becomes problematic due to non-zero closure phase. The errors induced by non-zero phase closure can be avoided by the use of single-look phases for all scatterers, including distributed scatterers. A weighted least-squares solution of the deformation time-series is obtained using the multi-reference stack interferometric single -look phases. Quality control is done during the regression analysis, the conversion to the time series, and considering the temporal coherence. Spatial filtering of the single-look phase time series can be used to further reduce the phase noise present in areas with intermediate coherence levels. [ABSTRACT FROM AUTHOR]

We compare the processing of Persistent Scatterer Interferometry data in map geometry versus their processing in slant-range/azimuth radar coordinates. In mountainous areas, using the map geometry significantly reduces the geometric distortion of radar coordinates that places scatterers that are actually widely separated in altitude in very close proximity in terms of slant-range. Processing in slant-range coordinates over mountainous regions introduces distortion in the distances used for estimation and filtering of tropospheric phase and phase unwrapping. Spatial filtering, interpolation of missing values, and phase unwrapping have better performance in map geometry because the distances between points are closer to reality. Performing these steps in a map geometry results in a more robust and more reliable processing chain. [ABSTRACT FROM AUTHOR]

• Correlation structure of ionosphere over China was analysed. • An undersampled threat model was developed for China area. • 1500km fit radius and 0.5m decorrelation value are derived with correlation result. • 1500km fit radius and RCM less than 0.5 are suggested with the spatial threat model. Satellite Based Augmentation Systems (SBAS) broadcasts to users Grid Ionospheric Vertical Delays (GIVDs) and associated confidence bounds called Grid Ionospheric Vertical Errors (GIVEs) at Ionospheric Grid Points (IGPs). The correlation structure of ionosphere and undersampled threat should be taken into account in the generation of GIVE to meet the integrity requirement. In this contribution, the correlation structure of ionosphere over China was investigated and a primary undersampled threat model was built for the development of BDSBAS. Planar fit algorithm was used to estimate the GIVDs, the correlation structure was yielded from the differences and residuals of the vertical delays at Ionospheric Pierce Points (IPPs). Then undersampled threat model was created with data deprivation method. Five days' data collected by 24 stations spread over China was selected to perform the correlation analysis and develop the threat model. Based on the correlation analysis, a maximum fit radius of 1500 km and a decorrelation value of 0.5 m were recommended for China area. Due to the ionospheric irregularity which could affect the region under the latitude of 30°N, a fit radius of 1300 km was suggested to improve the system availability. With the spatial threat model, it was found high latitude region owned a smaller threat value due to the relative quiet ionospheric condition. Relative Centroid Metric (RCM) less than 0.5 was proposed for determining the locations of BDSBAS' sites. Threat models derived with different cut-off elevation angle were investigated and 5° elevation mask was proposed to generate the threat model. [ABSTRACT FROM AUTHOR]

The next-generation of satellite-based augmentation system (SBAS) will employ a dual-frequency multi-constellation (DFMC) service providing several advantages over the classical SBAS L1 service. In September 2017, a two-year SBAS test-bed was initiated by Australia and New Zealand in preparation for building an operational system. This system includes DFMC SBAS in addition to the legacy SBAS L1 service and real-time precise point positioning (PPP) service over the Asia-Pacific region. In this paper, we focus on the new DFMC SBAS, and first discuss its positioning and integrity monitoring (IM) algorithms. Next, its performance is tested and analyzed using real DFMC SBAS data, restricting focus to LPV-200 in aviation. Based on real SBAS messages from the geostationary (GEO) satellite Inmarsat-4F1, testing was performed first at two known stations with actual GNSS observations, and next at simulated grids covering the entire Asia-Pacific region. A sensitivity analysis is performed, investigating the contribution of the error sources and the impact of changing the satellite mask angle. Experimental results of 12 consecutive days from September 14 to 25, 2018 of the new SBAS products show that the dual-frequency correction (DFC) residual errors have the dominant contribution in the values of the protection levels needed in IM, whereas other error sources such as the airborne receiver errors, the tropospheric and the ionosphere residual errors have secondary impacts. The accuracy of the positions was found to be at the sub-meter to meter level and was always bounded by the protection levels (PLs) at the known stations. The simulated PLs were less than the alert limit of LPV-200 during the test period in most of the areas of interest, indicating the availability of IM using DFMC SBAS in the main areas of the Asia-pacific region. [ABSTRACT FROM AUTHOR]

On December 27, 2018, the Beidou-3 System (BDS-3) has completed the deployment of 18 Medium Earth Orbit (MEO) satellites combined as a space constellation. In addition to the augmentation information for the new system signals B1C and B2a, the BDS-3 is compatible with the three augmentation information broadcast by the BDS-2 system for B1I and B3I signals: equivalent clock error correction, User Differential Ranging Error (UDRE) and Grid Ionosphere Vertical Error (GIVE). In this paper, the observation data of Beidou monitoring network are used to analyze the pseudo-range observation quality of the smooth transition signals B1I and B3I of BDS-2 and BDS-3. At the same time, the relationship between the equivalent clock error correction and the prediction error of the satellite clock is analyzed by using the Two-Way Satellite Time and Frequency Transfer (TWSTFT) data. The results show that the correlation between the equivalent clock error correction and the monitored clock error by using the TWSTFT data is greater than 60%. We calculate the UDRE by using the equivalent clock error correction. The results show that the satellite equivalent clock error correction can improve the accuracy of User Equivalent Range Error (UERE) by about 50%. This paper also compares the positioning accuracy of the BDS-2 satellites with the BDS-2 satellites combined BDS-3 satellites. The results show that the three-dimensional positioning accuracy is improved by about 30% after the BDS-3 satellites are added. [ABSTRACT FROM AUTHOR]

Abstract The Kilauea volcano on the Hawaii island started erupting on 3rd May 2018 after an earthquake of magnitude 5.0. The initial volcano eruption and the subsequent earthquakes resulted in the opening of new volcanic fissures, continuous lava flow at the lower east rift zone and the collapse of the summit caldera floor. All these activities continued until the 1st week of August 2018. The Small Baseline Subset (SBAS) technique is an advanced form of Differential Interferometry (DInSAR) which is capable of monitoring surface deformations with millimetre level accuracy. SBAS technique was utilised here for estimating the surface deformation on Hawaii island due to the volcanic episode. InSAR coherence technique was also utilised in this study for localised analysis at the summit and at the lower east rift zone to detect the time series deformation information and lava flow patterns. 14 interferometric datasets acquired by the ESA's Sentinel-1 C-band satellite from April 2018 to September 2018 were used in this study. The data acquired by the seismometers installed at Kilauea by Hawaii Volcano Observatory, the SWIR band of Sentinel-2 and the thermal band of Landsat-8 were used to correlate and verify the results obtained through the SBAS and InSAR coherence analysis. The combined interpretation of results obtained from all the sources gave insights about the underground magma conduit system, surface deformations, lava flow channels and the correlation between the magmatic and seismic activity happened there which are discussed in detail in this paper. Highlights • Detected subsidence at the Kilauea summit and Puu Oo crater due to magma withdrawal • Increased seismic activity at summit due to Caldera floor collapse • Open channel lava flow from fissures at Leilani Estates • Lava delta formation due to ocean entry of lava flowing through open channel • Sub-terrain magma conduit from summit reservoir to Leilani Estates [ABSTRACT FROM AUTHOR]

Subsidence in coastal deltas is a challenging issue globally, influenced by both climate and anthropogenic pressures. Owing to its rich economic value, the Godavari Delta on the east coast of India attracts the human population and is therefore a hub of developmental activities. We quantified the line of sight (LOS) rate of land deformation in the Godavari Delta, India, for two different periods using the time series interferometric analysis of Advanced Land Observing Satellite Phase Arrayed L-band Synthetic Aperture Radar (ALOS PALSAR) (2007–2011) and C-band Sentinel-1A (2017–2020) datasets. This approach was based on the Small Baseline Subset (SBAS) algorithm, which constructed 76 (ALOS) and 333 (Sentinel-1A) pairs of interferograms. The results indicated that the majority of deltas had varying LOS deformation rates in both periods. The southern and northern coastline of the deltas showed subsidence (-10 to -20 mm/yr) and uplift (5 mm to 7 mm/yr), respectively, from 2007 to 2011. The uplift (11 mm/yr) during 2017–2020 was attributed to coastal erosion and accretion during the study period. Statistical analyses showed that the majority of the coastline experienced erosion from 2006 to 2011, ranging from 0 ‐30 m/yr. Conversely, during 2017–2019, accretion ranging from 0-30 m/yr was dominant. The Kakinada spit has recently experienced an uplift of 8 mm/yr. Many factors contributing to deformation, such as groundwater fluctuations, rainfall, land use and land cover (LULC) changes, and water quality, were explored. Groundwater level variations were strongly correlated with the rate of deformation. A direct relationship was also observed between water recharge through rainfall and the ground deformation rate. The subsidence rate was estimated as 0 to ‐8 mm/yr from 2007-2011 and -10 to -20 mm/yr for 2017–2020 in the Godavari Delta. Increased urban areas and land conversion from the LULC analysis were the causative factors of subsidence in this region. Thus, the Godavari Delta will become highly vulnerable, as the region has shown various LOS deformation rates. Studies on land subsidence are highly relevant for effective coastal management planning and management. • First study to explore the ground deformation in Godavari delta. • Role of freshwater influence and land use are discussed. • Brought out the human interventions in the Godavari delta. • Needed for environmental management of the Godavari delta. [ABSTRACT FROM AUTHOR]

In this work, we investigate the past and present land deformation in Al Wagan area in the United Arab Emirates. The area is primarily an agricultural region where dependence on groundwater is documented. Such a reliance on ground water resources in a region which is characterized by very low precipitation can lead to significant land subsidence as was observed in this study which identified fast and localized deformation trends. The quantification of ground deformations of large magnitude and small amplitude in this area with SAR Interferometry is a challenging task using moderate resolution data due to the incoherent surface background. Even though SAR acquisitions were sparse over this region, the available ENVISAT, ALOS and Sentinel-1A imagery was analysed with differential interferometry and the Small Baseline Subset technique in order to provide estimates about the evolution of the deformation pattern in a limited area. A clear evidence of subsidence phenomena has been identified in the study area. During the period 2003–2010 the subsidence was estimated to reach 18 cm/year as observed in the DInSAR processing results of data from ENVISAT and ALOS Satellites. However it appears to be slightly more stable during the recent past (Dec/2016–March/2018) as observed in the results with recent Sentinel-1 data where a maximum localized subsidence in the order of 10 cm was estimated. The depletion of the aquifer resources which is confirmed from groundwater level data is speculated to be the most probable cause. [ABSTRACT FROM AUTHOR]

The seasonal freeze/thaw variations of the active layer cause seasonal ground deformation, such as thaw subsidence in summer and frost heave in winter due to the cyclic phase changes of soil water. The Synthetic Aperture Radar (SAR) remote sensing, especially interferometric SAR (InSAR) techniques, has been proven to be a very useful tool for observing surface displacements of permafrost environments. Most previous studies on seasonal InSAR displacement have been concentrated in several study sites in the Arctic tundra regions. The objective of this study is to extend the InSAR analysis of seasonal ground deformations to boreal forest regions, where monitoring ground deformation is particularly important in terms of better understanding active layer dynamics under various ecological and geological conditions. In this study, we presented a strategy to analyze the time series SAR data in the freezing season to estimate the differential phase for seasonal ground deformation while overcoming the problem of coherence losses due to the rapid growth of vegetation during the short growing season. We applied the SBAS-based InSAR processing method to Sentinel-1 SAR in the central Yakutian lowlands, where boreal forests and thermokarst landforms are widely distributed, and retrieved frost-related displacement signals successfully. In addition to the magnitude of ground deformation in the freezing season, we further examined the temporal deformation pattern related to the progression of the freezing front in the soil during active freezing. Based on the Stefan solution, we proposed a piecewise linear model for the time series deformation. The proposed model divides the time series displacement according to the progression of freezing into three linear segments, and the slope parameter of each linear model can be interpreted as indicating the hydrological characteristics of the upper, middle, and lower parts of the soil. The results for the Yakutian lowlands illustrated the potential of SAR remote sensing to observe and quantify spatial details of the thermal and hydrological properties inside the active layer soil even in highly vegetated subarctic boreal forest areas. • Observation of seasonal deformation in boreal permafrost using Sentinel-1 data. • Timeseries InSAR analysis in the freezing season allows retrieval of deformation signals • It is possible to observe spatial details on frost-related ground deformation patterns. • A new model for the temporal InSAR displacement pattern is presented. • Physical properties inside the soil layer can be inferred from the temporal InSAR pattern. [ABSTRACT FROM AUTHOR]

Investigating the effects of the Equatorial Ionization Anomaly (EIA) ionosphere and space weather on Global Navigation Satellite Systems (GNSS) is very crucial, and a key to successful implementation of a GNSS augmentation system (SBAS) over the equatorial and low-latitude regions. A possible ionospheric vertical delay (GIVD, Grid Ionospheric Vertical Delay) broadcast at a Ionospheric Grid Point (IGP) and its confidence bounds errors (GIVE, Grid Ionospheric Vertical Error) are analyzed and compared with the ionospheric vertical delay estimated at a nearby user location over the West African Sub-Saharan region. Since African sub-Saharan ionosphere falls within the EIA region, which is always characterized by a disturbance in form of irregularities after sunset, and the disturbance is even more during the geomagnetically quiet conditions unlike middle latitudes, the need to have a reliable ionospheric threat model to cater for the nighttime ionospheric plasma irregularities for the future SBAS user is essential. The study was done during the most quiet and disturbed geomagnetic conditions on October 2013. A specific low latitude EGNOS-like algorithm, based on single thin layer model, was engaged to simulate SBAS message in the study. Our preliminary results indicate that, the estimated GIVE detects and protects a potential SBAS user against sampled ionospheric plasma irregularities over the region with a steep increment in GIVE to non-monitored after local sunset to post midnight. This corresponds to the onset of the usual ionospheric plasma irregularities in the region. The results further confirm that the effects of the geomagnetic storms on the ionosphere are not consistent in affecting GNSS applications over the region. Finally, this paper suggests further work to be investigated in order to improve the threat integrity model activity, and thereby enhance the availability of the future SBAS over African sub-Saharan region. [ABSTRACT FROM AUTHOR]

Entering the SAR's golden era began with the launch of Sentinel-1A/B satellites in 2014 and 2016 with 6–12 day revisit time, much larger stacks of high-resolution SAR images are available over a given area to perform time series analysis. Algorithms that deal with large stack sizes face several challenges, including interferometric phase quality degradation due to signal decorrelations, phase closure error caused by applied multilooking, and tropospheric phase delay. Here, we present an improved SBAS-type algorithm suitable for processing a large stack of SAR images at an arbitrary resolution. We develop a new pair selection strategy that applies dyadic downsampling combined with widely used Delaunay Triangulation to identify an optimal set of interferometric pairs that minimize systematic errors due to short-lived signals and closure errors. We develop and apply a novel statistical framework that selects elite pixels accounting for distributed and permanent scatterers. Also, we implement a new tropospheric error correction that takes advantage of smooth 2D splines to identify and remove error components with fractal-like structures. We demonstrate the effectiveness of the algorithms by applying them to 3 large datasets of Sentinel-1 SAR images measuring non-linear surface deformation over various terrains. Compared with independent GNSS observations, we find that over the rural/natural terrains adjacent to San Andreas fault in southern California, our approach yields a standard deviation of 0.48 cm for time series differences in both ascending and descending tracks. While in urban areas, such as Los Angeles, standard deviation difference with GNSS time series is 0.30 cm. • Present an improved SBAS-type algorithm for processing a large stack of SAR images. • Develop a new pair selection strategy to identify interferometric pairs. • Apply a novel statistical framework that selects elite pixels. • Implement a new tropospheric error correction that uses smooth 2D splines. [ABSTRACT FROM AUTHOR]

Interferometric synthetic aperture radar (InSAR) time-series analysis provides high spatial resolution and continuous temporal coverage for investigations of long-term ground displacement. Beijing, the capital city of China, has suffered from land subsidence since the 1950s, and extreme groundwater extraction has led to subsidence rates of > 100 mm/year. In this study, InSAR time-series analysis is performed on different data subsets to investigate the ground displacement at Capital International Airport, Beijing, between June 2003 and November 2013. The results show that the ground surface in the airport has deformed at different rates ranging from − 66.2 mm/year (sinking) to 8.2 mm/year (uplift) relative to the reference point. The projected vertical displacement rates agreed with measurements estimated from ground-leveling surveys, and the correlation coefficient of the fitting result is 0.96, with a standard deviation of 0.9 mm/year and a mean different of 2.0 mm/year. The runways and terminals have been affected by land subsidence to various degrees. Previous studies has indicated that long-term intense groundwater extraction is the main reason leading to land subsidence in this area. Other triggering factors, such as active faults, the quaternary compressible layers and urbanization, also have different degrees of contribution or impact on land subsidence in Beijing Plain. Furthermore, some interesting behaviors from groundwater (such as inter- and semi-annual variations) and subsidence, the relationship between them are also found in this study. [ABSTRACT FROM AUTHOR]

The dynamics of rock glaciers in marginal periglacial environments are poorly understood, especially in Eastern Europe where the enhanced continentality produces a distinct pattern of periglacial phenomena. Multi-temporal image analysis of high-resolution optical and radar satellite imagery of the Southern Carpathian Mountains, Romania revealed the small dynamic nature and a slow geomorphologic evolution of rock glaciers over a 46-yr period of record (1968–2014). Nine rock glaciers located in glacial cirques and troughs within the central area of Retezat Mountain were included in this study. Overall, the estimated displacement rates are extremely low (i.e., a few cm/year) compared with other active rock glaciers from all over the world. Despite their relative attenuated activity, it appears that Judele, Valea Rea, and Pietrele are still active rock glaciers, but in an evident disequilibrium/imbalance with the actual climate. These findings document the lowest altitude and easternmost active rock glaciers at this latitude from Europe. Quantitative investigations were concentrated on Pietrele rock glacier, subject of recent field campaigns. Optical data analysis indicated a slight acceleration of the horizontal velocities at the surface of Pietrele rock glacier in recent years. This acceleration appears to be caused by an increase in the temperature of permafrost, resulting from an evident warming of external air temperature. Radar data analysis suggested seasonal variability of surface motion, with higher deformation in autumn, whereas in early summer or spring the deformation is negligible. Overall, the results obtained with cross-correlation analysis, interferometric synthetic aperture radar (InSAR) coherence analysis, and Small BAseline Subset (SBAS) multitemporal interferometry, are consistent, displaying similar deformation patterns with the highest creep rates located in the southern and western portions of the glacier. These findings are supported by thermal and geophysical measurements, which suggest the probable presence of permafrost within these areas. The observed displacements were interpreted as permafrost creep, and their very low velocity rates suggest the deforming frozen layers are very thin. These results provide (i) baseline information and decadal-scale trends and a (ii) strategy for future monitoring of the health and integrity of the rock glacier environment in the Carpathian Mountains. [ABSTRACT FROM AUTHOR]

This paper aims to present some of the most popular multi-temporal differential interferometry (DInSAR) techniques that are used for monitoring surface deformations in different types of areas. We focus on the urban area of Bucharest, where we applied the PS (Persistent Scatterers) and SBAS (Small BAseline Subset) techniques. The PS approach analyzes interferograms generated with a common master image, looking at point targets that remain stable over time, generating signal that remains coherent from an acquisition to another. The SBAS approach relies on small baseline interferograms that maximize the spatial and temporal coherence. In this paper we compare these techniques by applying them to the urban area of Bucharest using TSX data.. Both PS and SBAS methods generate millimetre ground displacement rates. The PS subsidence values range from -22 mm/yr to 22 mm/yr while the SBAS value rates are lower, from -10 mm/yr to 10 mm/yr. The subsidence rate maps are compared from a quantitative and qualitative point of view, taking into account also the type of movements that the techniques can derive. The current paper is mainly methodological oriented, aiming to present the PS and SBAS techniques in a comparative way. Less emphasis is put on the initial results, which are presented briefly in order to give an insight about further study directions. [ABSTRACT FROM AUTHOR]

The Galapagos Archipelago in the Pacific Ocean, situated 1000 km from the Ecuadorian coast, has been considered one of the UNESCO World Heritage sites. Its geographical location, ongoing seismo_volcanic activities, and the island's extreme isolation have led to the development of a wide variety of unique plant and animal species, which inspired Charles Darwin's theory of evolution. La cumbre volcano is one of the most active volcanoes in the Galapagos archipelago and is situated closest to the mantle plume. Eruptions are frequent here, with a record of 30 eruptions since 1800. Recently La Cumbre volcano erupted on 2020 January 12, with 11 seismic tremors recorded on that day with a maximum magnitude of 4.7. The Small Baseline Subset (SBAS) is an advanced Differential Interferometric SAR technique used to generate the deformation time series from the sequence of SAR datasets with a reduced spatiotemporal decorrelation. It is one of the best approaches for monitoring and analyzing surface deformations from space with a millimeter level of accuracy. In this paper, we analyze the January 2020 eruption of the La cumbre volcano using the SBAS technique. 9 Sentinel-1C band SAR data granules from 2019 November 17 to 2020 February 21 were used to generate the deformation time series map for estimating the degree of deformation at the volcanic edifice. As per the analysis, it is evident that the recent eruption has caused a displacement of up to −38 cm at the South Eastern flank of the crater, which has increased initially and then decreased on approaching the steady-state of eruption. • SBAS-DInSAR Analysis for the volcanic eruptions of La cumber volcano • The volcanic eruption was triggered by Earthquake. • La cumbre is the youngest volcano of the Galapagos Archipelago • La cumbre is characterized by its giant caldera, and flank fissures. • Understanding the association between the seismic and magmatic activities [ABSTRACT FROM AUTHOR]

The recent publication of the advanced Required Navigation Performance (RNP) specifications enable constantly precise aircraft path guidance without demanding expensive equipment and crew certification from the operator. Combined with the operational roll-out of satellite based regional augmentation for Global Navigation Satellite Systems (GNSS), it enables new possibilities such as implementing instrument approach procedures at airports, whose location previously forbade such. Here, we design and flight test two advanced RNP procedures at the airports of Saarbrücken and Egelsbach containing a fixed radius turn which terminates at the final approach fix of a 3D guided final. Results show that the track can be followed with a precision of below 0.1 nautical miles both in manual and in automatic flight with a light piston twin aircraft and with a fast business jet. Effectively, the procedures presented in this paper decouple Saarbrücken airport from French airspace and Egelsbach airport from the high density traffic of the Frankfurt (Main) International control zone. [ABSTRACT FROM AUTHOR]

Mapping slope movements in Alpine environments is an increasingly important task in the context of climate change and natural hazard management. We propose the detection, mapping and inventorying of slope movements using different interferometric methods based on TerraSAR-X satellite images. Differential SAR interferograms (DInSAR), Persistent Scatterer Interferometry (PSI), Short-Baseline Interferometry (SBAS) and a semi-automated texture image analysis are presented and compared in order to determine their contribution for the automatic detection and mapping of slope movements of various velocity rates encountered in Alpine environments. Investigations are conducted in a study region of about 6 km × 6 km located in the Western Swiss Alps using a unique large data set of 140 DInSAR scenes computed from 51 summer TerraSAR-X (TSX) acquisitions from 2008 to 2012. We found that PSI is able to precisely detect only points moving with velocities below 3.5 cm/yr in the LOS, with a root mean squared error of about 0.58 cm/yr compared to DGPS records. SBAS employed with 11 days summer interferograms increases the range of detectable movements to rates up to 35 cm/yr in the LOS with a root mean squared error of 6.36 cm/yr, but inaccurate measurements due to phase unwrapping are already possible for velocity rates larger than 20 cm/year. With the semi-automated texture image analysis the rough estimation of the velocity rates over an outlined moving zone is accurate for rates of “cm/day”, “dm/month” and “cm/month”, but due to the decorrelation of yearly TSX interferograms this method fails for the observation of slow movements in the “cm/yr” range. [ABSTRACT FROM AUTHOR]

The foreland fold-and-thrust belt of northern Pakistan is located at the western end of the Himalayan arc, where salt tectonics is responsible for structural styles, hydrocarbon source areas and seismicity. Three sub-regions of fold-and-thrust belt are the Potwar Plateau–Salt Range, Kohat Plateau–Surghar Range and the Bannu Basin–Khisor Range. The difference in deformation intensity between these regions is mainly attributed to the presence, or absence, of an Infra-Cambrian salt layer. This study investigates the active tectonics of the Potwar Plateau and Salt Range region, emphasizing the role of salt, using the Small Baseline Subset Interferometry (SBAS) technique and 2-D seismic interpretations. Ten PALSAR images and four seismic profiles from western Potwar Plateau–Salt Range region were used. SBAS results, derived from PALSAR images spanning from 2007 to 2010, suggest that the Potwar Plateau–Salt Range is active with the western portion of the region experiencing an uplift at an average rate of around 10 mm/year. Two uplift anomalies were observed, which were interpreted as zones of transpression and salt diapirism. Time-migrated seismic profiles show that the salt layer acts as a detachment. Our results show that salt has different roles in different regions of the fold-and-thrust belt; in the Potwar Plateau region the salt layer acts as a detachment, while in Salt Range salt flow-induced structures are prominent. The integration of SBAS and 2D seismic interpretation reveals that the deformation of western Potwar Plateau–Salt Range is influenced by two main faults, the dextral Kalabagh fault and the Main Frontal Thrust. Finally, this work was compared to the Kuqa fold-and-thrust belt in western China due to their structural similarities. [ABSTRACT FROM AUTHOR]

The groundwater in Tucson, Arizona, is a major source for water supply to human residential areas and agricultural use, and the groundwater extraction causes ground deformation responding to aquifer-system compaction. Using multi-temporal C-band and L-band SAR images from ERS/ENVISAT and ALOS PALSAR satellites, we mapped the ground displacement in Tucson. The InSAR-derived ground displacement based on small baseline subset technique (SBAS) is compared to compaction from extensometers, land subsidence from GPS survey, and groundwater elevation at wells. Tucson is characterized by slow and relatively small subsidence over areas with upper stratigraphic till early 2000s when the groundwater had been extremely depleted and by uplifts in areas where the water level has been recently recovered into the slight increase of water table because of recharge into the aquifer. Our multi-sensor SBAS InSAR-derived vertical displacements enabled to monitor the temporal variability in the spatial extent and magnitude of the ground deformation, suggesting that recent ground subsidence is slowing down and the ground motion in places is stable. Our results can provide scientific basis for sound management of ground water pumping and recharge over the study area. [ABSTRACT FROM AUTHOR]

This paper describes the main ideas of a GNSS SDR receiver and its implementation. Aims of the development, advantages, and some specific details are discussed. Particular attention is paid to the issue of security in GNSS receivers used for special purposes and some strategies of tracking. The idea of a snapshot receiver is briefly mentioned. [ABSTRACT FROM AUTHOR]

Sinkholes in karst areas may cause subsidence damage in transportation infrastructures, demolition of buildings and even the loss of human lives when they occur in a catastrophic way. Differential Interferometry (DInSAR) is a promising technology for detecting and characterizing sinkholes, as well as for reducing the associated risk when combined with other sources of data such as a sinkhole inventory. In this work, the usefulness of InSAR techniques and data for sinkhole risk management has been analyzed through the comparison of three DInSAR-derived velocity maps with a comprehensive sinkhole inventory in the Ebro Valley, NE Spain. The DInSAR maps have contributed to improve the sinkhole inventory in different ways: (1) detection of non-inventoried sinkholes; (2) revision of sinkhole areas previously classified as inactive as active; and (3) refinement of underestimated sinkhole boundaries. The obtained results suggest that DInSAR products are suitable for analyzing active dissolution-induced subsidence. The application of these techniques may help in recognizing and better characterizing previously unknown karst subsidence problems and in preventing personal and property losses. However, the analysis reveals that the available DInSAR maps combined overlook about 70% of the previously mapped active sinkholes mainly due to decorrelation. [ABSTRACT FROM AUTHOR]

Abstract: Advancement in augmented satellite navigation enables a new class of instrument approach procedures for aircraft. These approaches are based on regional augmentation systems which broadcast corrections via a geostationary satellite. The enhanced GNSS navigation solution using the corrections from the satellite provides the necessary accuracy and integrity to perform approaches with vertical and lateral angular guidance to a given runway threshold. This enables cost effective and simple procedure generation with low descent minima even for small airports. Moreover, it supports high precision en-route navigation and future high precision flight guidance applications. [Copyright &y& Elsevier]

Abstract: We extensively exploit advanced Differential SAR Interferometry (DInSAR) techniques for enhanced landslide investigations. We focus on the Ivancich area, Assisi, Central Italy, which is affected by a deep-seated landslide investigated through in-situ surveys. For this area, large data sets of SAR acquisitions were collected by the C-band ERS-1/2 and ENVISAT sensors (from April 1992 to November 2010), and by the X-band radars of the COSMO-SkyMed (CSK) constellation (from December 2009 to February 2012). We concentrate on the advanced DInSAR technique referred to as Small BAseline Subset (SBAS) approach, benefiting of its capability to generate deformation time series at full spatial resolution and from multi-sensor SAR data. This allows us to present one of the first examples for a landslide area of ERS-1/2 — ENVISAT deformation time series exceeding 18 years. The results allowed characterizing the long-term behaviour of the landslide, and identifying sectors of the unstable slope affected by different deformation dynamics. Analysis of the CSK data set, characterized by a reduced revisit time and improved spatial resolution, resulted in a 15-time larger point density with respect to the ERS-ENVISAT measurements, allowing to investigate nearly all the buildings (and, in many cases, portions of buildings) in the landslide area. Lastly, we present an innovative modelling approach based on the effective integration of the DInSAR measurements with traditional geological and geotechnical information, providing deeper insights on the kinematical evolution of the landslide. We consider our analysis a prototype example that can be extended to different geological and geotechnical conditions, providing significant advances in the understanding of ground deformations induced by active landslides. [Copyright &y& Elsevier]

In recent years, two-dimensional (2D) materials that have ferroelectric, valley polarization as well as topological order is a major focal topic of nanomaterials research. We studied the monolayer (ML) SbAs(CH 2 OCH 3) 2 based on first-principles calculations. The adsorption energy results and phono spectra results show that the structure are stable. The in-plane ferroelectricity can be adjusted by rotating functional groups, CH 2 OCH 3 -. Chosen a suitable substrate (for example, diagonal boron nitride), an in-plane electric field can be supplied to control the ferroelectric switch. The topological order can be adjusted by stress stretching. After 6% tensile stress, it represents the quantum spin Hall effect. Considering energy band of spin polarization, it shows that the spin-splitting Dirac states at the K and -K valleys have opposite spin moments. The discovery of coexisting ferroelectric, valley polarization and topology in functional 2D materials opens a way for non-volatile memory storage and spintronics applications. • The in-plane ferroelectricity of ML SbAs(CH 2 OCH 3) 2 can be adjusted by rotating functional groups. • The topological order can be adjusted by stress stretching. • The spin-splitting Dirac states at the K and -K valleys have been observed. [ABSTRACT FROM AUTHOR]

We present a novel methodology for integration of multiple InSAR data sets for computation of two dimensional time series of ground deformation. The proposed approach allows combination of SAR data acquired with different acquisition parameters, temporal and spatial sampling and resolution, wavelength and polarization. Produced time series have combined coverage, improved temporal resolution and lower noise level. We apply this methodology for mapping coal mining related ground subsidence and uplift in the Greater Region of Luxembourg along the French–German border. For this we processed 167 Synthetic Aperture Radar ERS-1/2 and ENVISAT images acquired between 1995 and 2009 from one ascending (track 29) and one descending (track 337) tracks and created over five hundred interferograms that were used for time series analysis. Derived vertical and east–west linear deformation rates show with remarkable precision a region of localized ground deformation located above and caused by mining and post-mining activities. Time series of ground deformation display temporal variability: reversal from subsidence to uplift and acceleration of subsidence in the vertical component, and horizontal motion toward the center of the subsidence on the east–west component. InSAR results are validated by leveling measurements collected by the French Geological Survey (BRGM) during 2006–2008. We determined that deformation rate changes are mainly caused by water level variations in the mines. Due to higher temporal and spatial resolution the proposed space-borne method detected a larger number of subsidence and uplift areas in comparison to leveling measurements restricted to annual monitoring of benchmark points along roads. We also identified one deformation region that is not precisely located above the mining sites. Comparison of InSAR measurements with the water levels measured in the mining pits suggest that part of the water that filled the galleries after termination of the dewatering systems may come from this region. Providing that enough SAR data is available, this method opens new opportunities for detecting and locating man-made and natural ground deformation signals with high temporal resolution and precision. [ABSTRACT FROM AUTHOR]

Abstract: The spatial–temporal evolution of surface displacement of Los Angeles area over 2003–2007 is measured with weighted least squares (WLS) small baseline (SB) DInSAR technique. 32 small baseline interferograms are generated from 18 SAR images acquired by the ENVISAT satellite and separated into two independent subsets. An additional interferogram with a longer baseline but good interferometric quality is used to link the two subsets. A time series of displacements with their corresponding standard deviations (STD) are derived from the WLS DInSAR solution by considering the interferometric displacement variances when determining the weighting scheme. Both the long-term trends and the seasonal variations of the displacements in the area are determined in the study and validated with GPS measurements from a number of stations of the Southern California Integrated GPS Network (SCIGN). The mean line-of-sight (LOS) displacement velocity map shows up to 3cm/year of ground motion and up to 10cm of accumulated displacements in Santa Fe Springs and −8cm in Pomona over 2003–2007. Seasonal variations are identified in Santa Ana basin, the San Gabriel valley and the Lytle Creek basin, respectively. [Copyright &y& Elsevier]

Abstract: The introduction of a European space-based satellite augmentation system (SBAS) named EGNOS promises a strong business case by reducing communication, navigation, and surveillance (CNS) cost through the replacement of precision approach NAV facilities like instrument landing system (ILS) stations at airports by permitting satellite-based approaches. Unfortunately, the system fails to cover areas that could strongly benefit from space-based augmentation, such as Greenland, for instance, a semi-autonomous dependency of Denmark which unlike the Danish state is not part of the European Union. Whilst the American WAAS system coverage ends just east of Canada, full EGNOS availability is limited to as far west as Iceland and only permits GNSS non-precision approaches with lateral guidance in Greenland. The large island is thus stuck within two SBAS systems which would be highly useful at its airports that rely heavily on expensive ground stations whilst having a thin income base. This is an illustrative example of remote regions being left out from larger-scale developments in ATM, even if they could benefit disproportionately. [Copyright &y& Elsevier]

Abstract: We demonstrate here a computer code for calculation of time series and also mean and linear deformation rates from a set of coregistered unwrapped differential interferograms using a linear least-squares inversion technique based on the small baseline subset (SBAS) algorithm. The computer code is written in C and uses a singular value decomposition (SVD) routine from the LAPACK library and the fast Fourier transform for spatial filtering from the FFTW library. Various offset estimation and topographic correction algorithms are implemented, including simultaneous inversion for deformation rates and residual topographic error. This approach is particularly useful when applied to ALOS PALSAR interferograms that are coherent even at large perpendicular baselines and acquired with orbital parameters correlated with the time of acquisition. This methodology is applied to produce time series of ground deformation at Tauhara and Wairakei geothermal fields (Taupo Volcanic Zone, North Island, New Zealand) from 12 ALOS PALSAR images acquired between July 2007 and December 2009. We also present here a high-resolution deformation map of the ground subsidence caused by the extraction of geothermal groundwater for power generation, with maximum rates of subsidence of about 7cm/y. [Copyright &y& Elsevier]

Abstract: Rockslides have a high socioeconomic and environmental importance in many countries. Norway is particularly susceptible to large rockslides due to its many fjords and steep mountains. One of the most dangerous hazards related with rock slope failures are tsunamis that can lead to large loss of life. It is therefore very important to systematically identify potential unstable rock slopes. Traditional landslide monitoring techniques are expensive and time consuming. Differential satellite interferometric synthetic aperture radar (InSAR) is an invaluable tool for land displacement monitoring. Improved access to time series of satellite data has led to the development of several innovative multitemporal algorithms. Small baseline (SB) methods are based on combining and inverting a set of unwrapped interferograms that are computed with a small perpendicular baseline in order to reduce spatial phase decorrelation. Another well proven technique is the persistent scatterer interferometric method (PSI) that is based on analysis of persistent point targets. In this paper, we apply both approaches to study several rockslide sites in Troms County in the far north of Norway. Moreover, we take the opportunity to address the difference and similarities between the SB and the PSI multitemporal InSAR methods for displacement studies in rural terrain. [Copyright &y& Elsevier]

Abstract: Ionospheric disturbances are known to have adverse effects on the satellite-based communication and navigation. One particular type of ionospheric effects, observed during major geomagnetic storms and threatening the integrity performance of both ground-based and space-based GNSS augmentation systems, is the sharp increase/decrease in the ionospheric delay that propagates in horizontal direction, thus called for convenience ‘moving ionospheric wall’. This paper presents preliminary results from researching such anomalous ionospheric delay gradients at European middle latitudes during the storm events of 29 October 2003 and 20 November 2003. For the purpose, 30-s GPS data from the Belgian permanent network was used for calculating and analysing the slant ionospheric delay and total electron content values. It has been found that, during these two particular storm events, substantial gradients did occur in Europe although they were not so pronounced as in the American sector. [Copyright &y& Elsevier]

Landslides originating from remote steep slopes render people living downhill vulnerable, unaware of the impending danger. Identifications of slow-moving mountain slopes are possible now due to time series measurement from space using microwave satellite data and the InSAR technique, which potentially can detect displacement at millimetre level. Availability of open-source Sentinel-1 data has revolutionised the study involving landslide kinematics and predicting the time of failure. However, identification of accelerating trend, demarcation of release area and prediction of flow path after failure initiation are still challenging. In this paper, we present a novel method for time and path prediction of landslides using two large landslides (Kikruma and Kotropi) located in the Himalayas in India. Sentinel-1 data stack was processed using the Persistent Scatterer and Small Baseline Subset interferometric techniques to analyse the trend of ground deformation leading to slope failures. The displacement time series of the measurement points, analysed using inverse velocity and modified inverse velocity methods, show that the instability had commenced almost a year or more with the final onset of acceleration triggered by heavy rainfall, couple of weeks prior to the actual failure. The acceleration image created from displacement time series data was clustered using image segmentation techniques to demarcate the release area of landslides. The flow simulation was done using the Voellmy friction model with a high-resolution DEM to predict the flow path. The analysis done for Kikruma and Kotropi landslide case studies with the proposed method provided a safe prediction of the time of landslide with ~90% accuracy of the flow path prediction. Results show that the method demonstrated in this study may evolve as an effective tool for landslide early warning in hilly areas. • A novel method to map landslide release area from InSAR derived slope acceleration. • PSI and SBAS are used to detect the deformation trend leading to slope failures. • Velocity (Inverse and Modified Inverse) are used for failure time prediction. • Flow path simulated using the Voellmy friction model. [ABSTRACT FROM AUTHOR]

We present a quantitative assessment of the capability of the differential SAR interferometry (DInSAR) technique referred to as Small BAseline Subset (SBAS) approach to investigate fault creep phenomena. In particular we have computed, via the SBAS-DInSAR algorithm, time series of the surface displacements relevant to the Hayward fault zone, within the San Francisco Bay Area (California), from the European Space Agency''s ERS-1/2 satellite radar data for the 1992 to 2000 time period. Starting from the DInSAR time series we measured the relative displacements across the fault with no need for any atmospheric filtering step. These results have been systematically compared to the measurements available from the alignment arrays that are located along the fault. Our analysis shows that the standard deviation of the differences between the DInSAR and the in situ measurements is on the order of 2 mm. Moreover, the estimated mean deformation rates have an accuracy that is better than 1 mm/year. [Copyright &y& Elsevier]

To address increasing water demands in expanding cities, many aquifers in Mexico are overexploited and deplete. The resulting land subsidence often combines with ground faulting/fracturing and damage to infrastructure. This study provides the longest Synthetic Aperture Radar (SAR) survey ever undertaken for the Aguascalientes Valley, aimed to constrain its structurally-controlled subsidence process and the induced risk. 275 ERS-1/2 1996–2002, ENVISAT 2003–2010 and Sentinel-1 2014–2020 C-band SAR images are processed with change detection, differential Interferometric SAR (InSAR) and Small Baseline Subset (SBAS) methods. Aguascalientes notably expanded over the last four decades, as revealed by Seasat 1978 L-band SAR, Landsat 1985–2010 and Sentinel-2 2020 optical imagery. The observed subsidence pattern involves alluvial/fluvial deposits within the N-S trending graben. Maximum settlement rates are −14 cm/year in 1996, −10 cm/year in 2000–2010 and over −12 cm/year in 2015–2020. An acceleration (−0.70 cm/year2) is recorded in 2015–2020 close to recently developed industrial plants and housing districts. Satellite estimates agree with in-situ observations, static GPS surveying and continuous GPS monitoring data. Rough correlation is found with piezometric level drop rates, whereas aquifer thickness plays a stronger role in the subsidence process. While these outcomes align with the existing literature, this InSAR survey: (i) unveils previously unknown E-W deformation affecting two N-S oriented bands within the valley, with up to ~ ±3 cm/year in 2015–2020 towards its center; (ii) identifies zones of sagging and hogging with horizontal strain (ε) of up to 0.05–0.1%; (iii) retrieves differential rates reaching 6–8 cm/year and angular distortions (β) of 1/500 along the Oriente fault; and (iv) investigates the statistical distribution of β across field surveyed faults and fissures, and marks areas with potentially yet-unmapped ground discontinuities. A new surface faulting risk matrix embedding β and ε is therefore proposed to estimate subsidence impact on properties and population. Given its scale-dependency, the risk assessment provides a lower bound to the percentage of urban areas at risk within the Aguascalientes state: at least 2% of the urban areas were at high and very high risk in 2003–2010 (involving ~12,000 properties and ~39,000 inhabitants), but this increased to 6% in 2015–2020 (~25,600 properties, ~85,200 inhabitants). The evidence of a subsidence process evolving spatially and temporally highlights the need for continuous updating of hazard information. • Subsidence in Aguascalientes is unveiled with ERS-1/2, ENVISAT and Sentinel-1 InSAR. • Up to −12 cm/year vertical and ±3 cm/year E-W rates are observed in 2015–2020. • Subsidence acceleration is recorded near new industrial/housing developments. • Angular distortions reach 1/500 and horizontal strain 0.1% along surface faults. • 6% urban areas are at high to very-high risk in 2015–2020, i.e. ~85,200 inhabitants. [ABSTRACT FROM AUTHOR]

Among the fastest sinking cities globally, the metropolitan area of Mexico City is the target of an unprecedented satellite investigation based on over 300 Sentinel-1 Synthetic Aperture Radar (SAR) Interferometric Wide swath mode scenes acquired in 2014–2020. Two-pass differential Interferometric SAR (InSAR) and the parallelized Small BAseline Subset (SBAS) repeat-pass InSAR approach provide a complete account of spatial patterns, long-term trend and present-day settlement rates affecting the city. The 3D deformation field reveals that foremost is the role of the vertical velocity V U , with peaks of −38.7 cm/year in Nezahualcóyotl, −32.0 cm/year in Gustavo A. Madero and Venustiano Carranza, and −39.1 cm/year in Iztapalapa. Settlement at the metropolitan Cathedral in Cuauhtémoc is ongoing at up to −8.8 cm/year, consistently with the last six decades. Volcanic edifices mark ground stability "islets" inside the main subsidence bowls. East-west rates are limited, except for some horizontal strain (up to ±5 cm/year) within the subsidence bowls. Comparison with surface geology and geotechnical zoning confirms that aquitard compaction is the predominant process. The power relationship between V U [cm/year] and the thickness of lacustrine clay deposits H C [m] is: V U = 1 76 ∗ H C 1.8. The 2019–2020 deformation scenario shows that subsidence still involves most of Nezahualcóyotl, with −3.0 cm/month V U. A well-defined long-term deformation behaviour comes out from 2014–2019 InSAR time series and comparison with 2008–2020 GPS data. RMSE of 0.9 cm is found at MMX1 station deployed within the lacustrine unit, and 0.6 cm at TNGF station onto hard volcanic rocks. The sharpest subsidence gradients and angular distortions β in 2017–2019 (up to over 1/400, i.e. 0.14°) – thus the greatest vulnerability to surface faulting and cracking as a consequence of large tensile stress in the soil caused by differential settlement – are found at the foothills of Sierra de Santa Catarina, Peñón del Marqués, Cerro Chimalhuachi, Peñón de los Baños and Sierra de Chichinautzin, where the transition unit is narrower (or absent). Faults and cracks develop where β > 1/3000, i.e. 0.03%, in 2017–2019. The observed width of the influence zone (i.e. damage band), where β is still significant to induce damage, is 250 m. Differential settlement and surface faulting could compromise the serviceability of housing and utility infrastructure. It is estimated that over 457,000 properties and 1.5 million inhabitants of the Valley of Mexico Metropolitan Area (ZMVM) are in zones at high to very high surface faulting risk, mainly in Iztapalapa, Tláhuac, Chimalhuacán and Chalco. Increased flood exposure due to formation of topographic depressions involves over 751,000 properties and ~2.7 million inhabitants of the ZMVM, mainly in Nezahualcóyotl, Tláhuac, Venustiano Carranza, Iztapalapa, Gustavo A. Madero and Ecatepec de Morelos. These municipalities are often hit by catastrophic floods. • Over 300 Sentinel-1 SAR scenes are used to monitor land subsidence in Mexico City. • InSAR reveals vertical displacement rates as high as −39 cm/year in 2014–2020. • Urban infrastructure is vulnerable to cracking, as angular distortions reach 1/400. • 1.5 million inhabitants live in zones at high to very high risk of surface faulting. • Increased flood exposure due to subsidence involves over 751,000 properties. [ABSTRACT FROM AUTHOR]

• Peatland degradation due to the 2015 El Niño event has been identified. • The subsidence and land cover have been estimated using the Sentinel-1A SAR images. • Drainage networks have significant impacts on the subsidence patterns. • Vegetation cover degradation is correlated with the hotspot distribution. • The 2015 El Niño significantly increased subsidence and vegetation degradation. Indonesia has the world's largest tropical peatland, mostly located in the southern province of Sumatra, the south of Kalimantan, and Papua. The catastrophic fires between June and October 2015 induced by the El Niño event burnt most of these peatland areas. We analyzed spatio-temporal peat subsidence during pre- and post-fires in the peat hydrological unit of Sungai Sugihan – Sungai Saleh (KHGSS), South Sumatra using Sentinel-1 images by applying DInSAR-SBAS algorithm. Based on our analysis, the linear subsidence rate after the 2015 peat fires increased by a factor 6.4 compared to that of pre-fires. Generally, the estimated subsidence is temporally well-correlated with the precipitation variation. In addition, the subsidence patterns are spatially correlated with the hotspot distribution, peat thickness, and drainage networks. Furthermore, we mapped vegetation cover over the KHGSS by using the Sentinel-1 images as well. The results show that the vegetation degradation is correlated with the hotspot distribution and the highly-degraded vegetation associated with the 2015 peat fires. It demonstrated that the 2015 El Niño event has significant impacts on increasing the amount of the subsidence and the vegetation degradation in KHGSS area. [ABSTRACT FROM AUTHOR]

Ionospheric delay error is one of the most significant error sources for single frequency SBAS (Satellite Based Augmentation System) users and its error bound is the key point for PL (protection level) calculation. To satisfy the integrity specifications for users anywhere in the service region, the error bound need to be inflated according to various threat. Among them, the undersampled threat plays an important role in the inflation. The fundamental reason for the undersampled threat lies in the disagreement of the linear planar model to the actual ionosphere characteristics, which cannot be accurately described by the discrete IPP (Ionospheric Pierce Point) samples. Ionosphere threat model is established to handle this problem. It uses historical irregular ionosphere data to generate the two-dimensional lookup table which illustrates the relationship between the IPP distribution and the maximum estimation error. How to abstract the metrics to describe the discrete two-dimensional IPP distribution is the key to the establishment of ionosphere threat model. In this paper, we conclude the properties of a 'good' metric from a physical point of view and propose the Relative COVerage (RCOV) metric. Based on the measured data from IGS (International GNSS Service) stations, taking the regions of Europe (20°N~70°N, −30°W~60°E) as an example, the ionosphere threat model based on RCOV metric is established and compared with the RCM (Relative Centroid Metric) model used in WAAS (Wide Area Augmentation System) and MSAS (MTSAT Satellite based Augmentation System). At the same time, the integrity of the ionosphere GIVE (Grid Ionosphere Vertical Error) results is verified. The experimental results show that under the experimental configuration given in this paper, the RCOV metric proposed can improve the system availability on the premise of meeting the integrity requirements. • We conclude the properties of a 'good' metric and propose the RCOV metric. • Taking the regions of Europe as an example, the RCOV threat model is established and compared with the RCM used in WAAS. • RCOV metric proposed can improve the system availability on the premise of meeting the integrity requirements. [ABSTRACT FROM AUTHOR]