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In recent years, phase linking (PL) methods in radar time-series interferometry (TSI) have proven to be powerful tools in geodesy and remote sensing, enabling the precise monitoring of surface displacement and deformation. While these methods are typically designed to operate on a complete network of interferograms, generating such networks is often challenging in practice. For instance, in non-urban or vegetated regions, decorrelation effects lead to significant noise in long-term interferograms, which can degrade the time-series results if included. Additionally, practical issues such as gaps in satellite data, poor acquisitions, or systematic errors during interferogram generation can result in incomplete networks. Furthermore, pre-existing interferogram networks, such as those provided by systems like COMET-LiCSAR, often prioritize short temporal baselines due to the vast volume of data generated by satellites like Sentinel-1. As a result, complete interferogram networks may not always be available. Given these challenges, it is critical to understand the applicability of PL methods on these incomplete networks. This study evaluated the performance of two PL methods, eigenvalue decomposition (EVD) and eigendecomposition-based maximum-likelihood estimator of interferometric phase (EMI), under various network configurations including short temporal baselines, randomly sparsified networks, and networks where low-coherence interferograms have been removed. Using two sets of simulated data, the impact of different network structures on the accuracy and quality of the results was assessed. These patterns were then applied to real data for further comparison and analysis. The findings demonstrate that while both methods can be effectively used on short temporal baselines, their performance is highly sensitive to network sparsity and the noise introduced by low-coherence interferograms, requiring careful parameter tuning to achieve optimal results across different study areas. [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]

• 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]

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]

Landslides are among the most intense geological disasters worldwide. Several remote sensing techniques have been used to study these phenomena over the last few decades, including Global Navigation Satellite Systems (GNSS) and Multi-Temporal Interferometric Synthetic Aperture Radars (MT-InSAR), in particular, Small Baseline Subset (SBAS) and Permanent Scatterer Interferometry (PSI). The University of Azuay and highway infrastructure (Cuenca - Ecuador) were affected by slow-moving landslides which in urban areas had more noticeable deformation effects due to their crowns. Furthermore, evidence indicates that the landslide toe was developed in a rural area. To study landslide boundary and deformation kinematics comprehensively, we need to observe two distinct scattering surfaces using SAR imagery (high coherence areas in the urban area and low coherence areas in the rural area). We can also observe different distributions in X- and C-bands due to the rural area covered by vegetation and trees at the toe of the landslide. Two sets of radar images were analyzed and compared for monitoring the aforementioned slow-moving landslide kinematics, including Sentinel1-A (S1-A) and COSMO-SkyMed (CSK). PSI and SBAS techniques have been used to measure the rate of surface deformation and displacement time series at CSK over the period (2017-2019) and S1-A units over the period (2015-2018), respectively. Furthermore, a GNSS station in the stable area was used as a reference station to integrate the PSI and SBAS results over space. Then, an unsupervised machine learning algorithm (K-medians) was used to determine the most appropriate intervals for preparing mean deformation rate maps. Finally, a comparison was made between the outputs obtained from this study and displacement recorded at two additional GNSS stations located in the area affected by deformation. As a result, by comparing and monitoring double-band SAR satellites and different SAR image processing techniques, it became possible to analyze the whole landslide of our case study appropriately. [ABSTRACT FROM AUTHOR]

A number of productive oil and gas fields are located in the Apsheron Peninsula of Azerbaijan. The primary goal of the presented study was to quantitatively assess the ground deformation rates of oil and gas fields, determine natural and man-made influencing factors and predict deformation trends. The determined maximum displacement rates of subsidence and uplift processes were -26 mm/y and +23 mm/y, respectively. However spatial density analysis of deformation velocity presented the natural patterns of uplift and subsidence tectonic processes. This allowed to determine that two oil and gas fields hold a higher probability of being affected by man-made oil and gas exploration activities, whereas the one oil field is affected by both natural and man-made processes. [ABSTRACT FROM AUTHOR]

The present study was aimed at comparing vertical and horizontal surface displacements derived from the Cosmo-SkyMED, TerraSAR-X and Sentinel-1 satellite missions for the detection of oil extraction-induced subsidence in the Tengiz oilfield during 2018–2021. The vertical and horizontal surface displacements were derived using the 2D decomposition of line-of-sight measurements from three satellite missions. Since the TerraSAR-X mission was only available from an ascending track, it was successfully decomposed by combining it with the Cosmo-SkyMED descending track. Vertical displacement velocities derived from 2D Decomposition showed a good agreement in similar ground motion patterns and an average regression coefficient of 0.98. The maximum average vertical subsidence obtained from the three satellite missions was observed to be −57 mm/year. Higher variations and deviations were observed for horizontal displacement velocities in terms of similar ground motion patterns and an average regression coefficient of 0.80. Fifteen wells and three facilities were observed to be located within the subsidence range between −55.6 mm/year and −42 mm/year. The spatial analyses in the present studies allowed us to suspect that the subsidence processes occurring in the Tengiz oilfield are controlled not solely by oil production activities since it was clearly observed from the detected horizontal movements. The natural tectonic factors related to two seismic faults crossing the oilfield, and terrain characteristics forming water flow towards the detected subsidence hotspot, should also be considered as ground deformation accelerating factors. The novelty of the present research for Kazakhstan's Tengiz oilfield is based on the cross-validation of vertical and horizontal surface displacement measurements derived from three radar satellite missions, 2D Decomposition of Cosmo-SkyMED descending and TerraSAR-X ascending line-of-sight measurements and spatial analysis of man-made and natural factors triggering subsidence processes. [ABSTRACT FROM AUTHOR]

The ground deformation phenomena are the result of the application of natural stress (tectonic) or anthropogenic stress (overexploitation of groundwater, embankment) on the soil. The land deformation may cause several impacts on the environment and human life. A good understanding of the deformation behaviour of the soil is essential to mitigate risks on the infrastructure and environment. In this study, a radar interferometry is carried out to analyse the mobility of an urban and suburban area of Greater Tunis region. The interferometric synthetic aperture radar (SAR) technique has been proven to be an effective methodology for detecting and monitoring soil displacement with millimetre accuracy and also, improving our understanding of the current deformations in the study area. Indeed, the application of differential SAR interferometry made it possible to determine the origin of the surface deformations related to natural or anthropic phenomena. In this paper, the interferometric method of small baseline subset (SBAS) developed by Berardino et al. 2002has been chosen, in order to monitor the spatial and temporal pattern of the deformation phenomena in Greater Tunis region. The analysis of Envisat ASAR (2003–2007, descending satellite orbit) and Sentinel 1B (2016–2018, ascending satellite orbit) SAR data allowed us to create deformation velocity maps associated with line of sight displacement time series. The results obtained by this method showed the existence of subsidence phenomenon in the urban areas (Tunis City) as well as in the rural areas (Mornag plain). In the first site (Tunis City), the subsidence rate reaches up to 13.98 mm/year and 19 mm/year during 2003–2007 and 2016–2018, respectively. The ground deformation that is detected around the region of Tunis Lake and Sebkhet Essijoumi, is probably due to the nature of the highly compressible and thickness alluvial deposits and whose substratum depth sometimes reaches more than 60 m. In the second studied site, ground subsidence was identified in the whole plain of Mornag. Indeed, the comparison between piezometric data and time series deformations shows that the trend of soil subsidence is coherent with the dynamic change in groundwater levels. Furthermore, the analysis of velocity deformation, geological data and hydrogeological information allows us to associate all the detected settlement patterns to groundwater overexploitation and compressible alluvium all over the plain. This overexploitation of groundwater in Mornag plain is mainly caused by the expansion of agricultural and industrial activities and the decrease in annual rainfall in recent years (from 2003 to 2018).

The present study was aimed at comparing vertical and horizontal surface displacements derived from the Cosmo-SkyMED, TerraSAR-X and Sentinel-1 satellite missions for the detection of oil extraction-induced subsidence in the Tengiz oilfield during 2018–2021. The vertical and horizontal surface displacements were derived using the 2D decomposition of line-of-sight measurements from three satellite missions. Since the TerraSAR-X mission was only available from an ascending track, it was successfully decomposed by combining it with the Cosmo-SkyMED descending track. Vertical displacement velocities derived from 2D Decomposition showed a good agreement in similar ground motion patterns and an average regression coefficient of 0.98. The maximum average vertical subsidence obtained from the three satellite missions was observed to be −57 mm/year. Higher variations and deviations were observed for horizontal displacement velocities in terms of similar ground motion patterns and an average regression coefficient of 0.80. Fifteen wells and three facilities were observed to be located within the subsidence range between −55.6 mm/year and −42 mm/year. The spatial analyses in the present studies allowed us to suspect that the subsidence processes occurring in the Tengiz oilfield are controlled not solely by oil production activities since it was clearly observed from the detected horizontal movements. The natural tectonic factors related to two seismic faults crossing the oilfield, and terrain characteristics forming water flow towards the detected subsidence hotspot, should also be considered as ground deformation accelerating factors. The novelty of the present research for Kazakhstan’s Tengiz oilfield is based on the cross-validation of vertical and horizontal surface displacement measurements derived from three radar satellite missions, 2D Decomposition of Cosmo-SkyMED descending and TerraSAR-X ascending line-of-sight measurements and spatial analysis of man-made and natural factors triggering subsidence processes.

The ground deformation phenomena are the result of the application of natural stress (tectonic) or anthropogenic stress (overexploitation of groundwater, embankment) on the soil. The land deformation may cause several impacts on the environment and human life. A good understanding of the deformation behaviour of the soil is essential to mitigate risks on the infrastructure and environment. In this study, a radar interferometry is carried out to analyse the mobility of an urban and suburban area of Greater Tunis region. The interferometric synthetic aperture radar (SAR) technique has been proven to be an effective methodology for detecting and monitoring soil displacement with millimetre accuracy and also, improving our understanding of the current deformations in the study area. Indeed, the application of differential SAR interferometry made it possible to determine the origin of the surface deformations related to natural or anthropic phenomena. In this paper, the interferometric method of small baseline subset (SBAS) developed by Berardino et al. 2002has been chosen, in order to monitor the spatial and temporal pattern of the deformation phenomena in Greater Tunis region. The analysis of Envisat ASAR (2003–2007, descending satellite orbit) and Sentinel 1B (2016–2018, ascending satellite orbit) SAR data allowed us to create deformation velocity maps associated with line of sight displacement time series. The results obtained by this method showed the existence of subsidence phenomenon in the urban areas (Tunis City) as well as in the rural areas (Mornag plain). In the first site (Tunis City), the subsidence rate reaches up to 13.98 mm/year and 19 mm/year during 2003–2007 and 2016–2018, respectively. The ground deformation that is detected around the region of Tunis Lake and Sebkhet Essijoumi, is probably due to the nature of the highly compressible and thickness alluvial deposits and whose substratum depth sometimes reaches more than 60 m. In the second studied site, ground subsidence was identified in the whole plain of Mornag. Indeed, the comparison between piezometric data and time series deformations shows that the trend of soil subsidence is coherent with the dynamic change in groundwater levels. Furthermore, the analysis of velocity deformation, geological data and hydrogeological information allows us to associate all the detected settlement patterns to groundwater overexploitation and compressible alluvium all over the plain. This overexploitation of groundwater in Mornag plain is mainly caused by the expansion of agricultural and industrial activities and the decrease in annual rainfall in recent years (from 2003 to 2018). [ABSTRACT FROM AUTHOR]

This research focused on the quantitative assessment of the surface deformation velocities and rates and their natural and man-made controlling factors at Tengiz Oilfield in Kazakhstan using the Small Baseline Subset remote sensing technique followed by 3D and 2D decompositions and cosine corrections to derive vertical and horizontal movements from line-of-sight (LOS) measurements. In the present research we applied time-series of Sentinel-1 satellite images acquired during 2018–2020. All ground deformation derivatives showed the continuous subsidence at the Tengiz oilfield with increasing velocity. 3D and 2D decompositions of LOS measurements to vertical movement showed that the Tengiz Oil Field 2018–2020 continuously subsided with the maximum annual vertical deformation velocity around 70 mm. Based on the LOS measurements, the maximum annual subsiding velocity was observed to be 60 mm. Cosine corrections of LOS measurements to vertical movement, however, revealed a maximum annual vertical deformation velocity of 77 mm. The vertical deformation confirmed typical patterns of subsidence caused by oil extraction. Detected east-west and north-south horizontal movements at the Tengiz field clearly indicated that the study area crossed by seismic faults is affected by natural tectonic processes. The overall RMSE of 3D decomposed vertical deformation in relationship to LOS measurements and cosine corrections were in the range of 10–13 mm and 6–8 mm, correspondingly. The results of the present research will support operators of oil and gas fields and also other types of infrastructure to evaluate the actual differences of InSAR ground deformation measurements against the required standards and the precision of measurements depending on the operational needs, timeframes and availability of radar imagery.

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This research focused on the quantitative assessment of the surface deformation velocities and rates and their natural and man-made controlling factors as the potential risks along the seismically active 70 km section of buried oil and gas pipeline in Azerbaijan using Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) and Small Baseline Subset (SBAS) remote sensing analysis. Both techniques showed that the continuous subsidence was prevailing in the kilometer range of 13–70 of pipelines crossing two seismic faults. The ground uplift deformations were observed in the pipeline kilometer range of 0–13. Although both PS-InSAR and SBAS measurements were highly consistent in deformation patterns and trends along pipelines, they showed differences in the spatial distribution of ground deformation classes and noisiness of produced results. High dispersion of PS-InSAR measurements caused low regression coefficients with SBAS for the entire pipeline kilometer range of 0–70. SBAS showed better performance than PS-InSAR along buried petroleum and gas pipelines in the following aspects: the complete coverage of the measured points, significantly lower dispersion of the results, continuous and realistic measurements and higher accuracy of ground deformation rates against the GPS historical measurements. As a primary factor of ground deformations, the influence of tectonic movements was observed in the wide scale analysis along 70 km long and 10 km wide section of petroleum and gas pipelines; however, the largest subsidence rates were observed in the areas of agricultural activities which accelerate the deformation rates caused by the tectonic processes. The diverse spatial distribution and variation of ground movement processes along pipelines demonstrated that general geological and geotechnical understanding of the study area is not sufficient to find and mitigate all the critical sites of subsidence and uplifts for the pipeline operators. This means that both techniques outlined in this paper provide a significant improvement for ground deformation monitoring or can significantly contribute to the assessment of geohazards and preventative countermeasures along petroleum and gas pipelines.

Lanzhou New District is the first and largest national-level new district in the Loess Plateau region of China. Large-scale land creation and rapid utilization of the land surface for construction has induced various magnitudes of land subsidence in the region, which is posing an increasing threat to the built environment and quality of life. In this study, the spatial and temporal evolution of surface subsidence in Lanzhou New District was assessed using Persistent Scatterer Interferometric Synthetic Aperture radar (PSInSAR) to process the ENVISAT SAR images from 2003-2010, and the Small Baseline Subset (SBAS) InSAR to process the Sentinel-1A images from 2015-2016. We found that the land subsidence exhibits distinct spatiotemporal patterns in the study region. The spatial pattern of land subsidence has evidently extended from the major urban zone to the land creation region. Significant subsidence of 0-55 mm/year was detected between 2015 and 2016 in the land creation and urbanization area where either zero or minor subsidence of 0-17.2 mm/year was recorded between 2003 and 2010. The change in the spatiotemporal pattern appears to be dominated mainly by the spatial heterogeneity of land creation and urban expansion. The spatial associations of subsidence suggest a clear geological control, in terms of the presence of compressible sedimentary deposits; however, subsidence and groundwater fluctuations are weakly correlated. We infer that the processes of land creation and rapid urban construction are responsible for determining subsidence over the region, and the local geological conditions, including lithology and the thickness of the compressible layer, control the magnitude of the subsidence process. However, anthropogenic activities, especially related to land creation, have more significant impacts on the detected subsidence than other factors. In addition, the higher collapsibility and compressibility of the loess deposits in the land creation region may be the underlying mechanism of macro-subsidence in Lanzhou New District. Our results provide a useful reference for land creation, urban planning and subsidence mitigation in the Loess Plateau region, where the large-scale process of bulldozing mountains and valley infilling to create level areas for city construction is either underway or forthcoming. [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 aim of the here presented research was to investigate the potential of two-pass differential InSAR, and advanced DInSAR techniques, such as Small Baseline Subset (SBAS) and Persistent Scatterers (PS) interferometry, in order to detect and monitor the temporal behaviour of surface deformations in selected areas of the Garhwal and Kumaon Himalaya. We present results from the surroundings of the town of Nainital, from the Mansa Devi Hills area, and the areas around the cities of Chamoli Gopeshwar and Joshimath. [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]

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]

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]

InSAR (Interferometric Synthetic Aperture Radar) cloud computing and the subtraction of LiDAR (Light Detection and Ranging) DEMs (Digital Elevation Models) are innovative approaches to detect subsidence in karst areas. InSAR cloud computing allows for analyzing C-band Envisat and Sentinel S1 SAR images through web platforms to produce displacement maps of the Earth's surface in an easy manner. The subtraction of serial LiDAR DEMs results in the same product but with a different level of accuracy and precision than InSAR maps. Here, we analyze the capability of these products to detect active sinkholes in the mantled evaporite karst of the Ebro Valley (NE Spain). We found that the capability of the displacement maps produced with open access, high-resolution airborne LiDAR DEMs was up to four times higher than InSAR displacement maps generated by the Geohazard Exploitation Platform (GEP). Differential LiDAR maps provide accurate information about the location, active sectors, maximum subsidence rate and growing trend of the most rapid and damaging sinkholes. Unfortunately, artifacts and the subsidence detection limit established at −4 cm/yr entailed important limitations in the precise mapping of the sinkhole edges and the detection of slow-moving sinkholes and small collapses. Although InSAR maps provided by GEP show a worse performance when identifying active sinkholes, in some cases they can serve as a complementary technique to overcome LiDAR limitations in urban areas. [ABSTRACT FROM AUTHOR]

This research focused on the quantitative assessment of the surface deformation velocities and rates and their natural and man-made controlling factors at Tengiz Oilfield in Kazakhstan using the Small Baseline Subset remote sensing technique followed by 3D and 2D decompositions and cosine corrections to derive vertical and horizontal movements from line-of-sight (LOS) measurements. In the present research we applied time-series of Sentinel-1 satellite images acquired during 2018–2020. All ground deformation derivatives showed the continuous subsidence at the Tengiz oilfield with increasing velocity. 3D and 2D decompositions of LOS measurements to vertical movement showed that the Tengiz Oil Field 2018–2020 continuously subsided with the maximum annual vertical deformation velocity around 70 mm. Based on the LOS measurements, the maximum annual subsiding velocity was observed to be 60 mm. Cosine corrections of LOS measurements to vertical movement, however, revealed a maximum annual vertical deformation velocity of 77 mm. The vertical deformation confirmed typical patterns of subsidence caused by oil extraction. Detected east-west and north-south horizontal movements at the Tengiz field clearly indicated that the study area crossed by seismic faults is affected by natural tectonic processes. The overall RMSE of 3D decomposed vertical deformation in relationship to LOS measurements and cosine corrections were in the range of 10–13 mm and 6–8 mm, correspondingly. The results of the present research will support operators of oil and gas fields and also other types of infrastructure to evaluate the actual differences of InSAR ground deformation measurements against the required standards and the precision of measurements depending on the operational needs, timeframes and availability of radar imagery. [ABSTRACT FROM AUTHOR]

Public safety and socio-economic development of the Jharia coalfield (JCF) in India is critically dependent on precise monitoring and comprehensive understanding of coal fires, which have been burning underneath for more than a century. This study utilizes New-Small BAseline Subset (N-SBAS) technique to compute surface deformation time series for 2017–2020 to characterize the spatiotemporal dynamics of coal fires in JCF. The line-of-sight (LOS) surface deformation estimated from ascending and descending Sentinel-1 SAR data are subsequently decomposed to derive precise vertical subsidence estimates. The most prominent subsidence (~22 cm) is observed in Kusunda colliery. The subsidence regions also correspond well with the Landsat-8 based thermal anomaly map and field evidence. Subsequently, the vertical surface deformation time-series is analyzed to characterize temporal variations within the 9.5 km2 area of coal fires. Results reveal that nearly 10% of the coal fire area is newly formed, while 73% persisted throughout the study period. Vulnerability analyses performed in terms of the susceptibility of the population to land surface collapse demonstrate that Tisra, Chhatatanr, and Sijua are the most vulnerable towns. Our results provide critical information for developing early warning systems and remediation strategies. [ABSTRACT FROM AUTHOR]

We present in this comment a Multi-Temporal SAR Interferometry (MT-InSAR) analysis showing that the results published by Milillo et al. (2019) in the Remote Sensing Journal, presenting the evidence of space geodetic observations relevant to displacements occurring before the collapse of the Morandi Bridge, happened in Genova (Italy) on the 14 August 2018, are questionable. In particular, we focus on the InSAR results obtained by Milillo et al. (2019) by processing the 3 m × 3 m resolution COSMO-SkyMed (CSK) data collected from ascending and descending orbits on the area of interest. These results, thanks to the high spatial resolution and the short revisit time characterizing this multi-orbit SAR dataset, represent the cornerstone of their analysis. The main findings of their study allow Milillo et al. to conclude that the InSAR processing of this COSMO-SkyMed dataset reveals the increased deformation magnitude over time of points located near the strands of the deck next to the collapsed pier, between 12 March 2017 and August 2018. In this comment, we show the results obtained by the IREA-CNR SAR team after processing the same ascending and descending CSK dataset, but by using two alternative and independent processing techniques: the Small BAseline Subset (SBAS) and the Advanced Tomographic SAR (TomoSAR) approaches, respectively. Our analysis shows that, although both the SBAS and the TomoSAR analyses allow achieving denser coherent pixel maps relevant to the Morandi bridge, nothing of the pre-collapse large displacements reported in Milillo et al. (2019) appears in our results, leading us to deeply disagree with the findings of their InSAR analysis. [ABSTRACT FROM AUTHOR]

This research focused on the quantitative assessment of the surface deformation velocities and rates and their natural and man-made controlling factors as the potential risks along the seismically active 70 km section of buried oil and gas pipeline in Azerbaijan using Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) and Small Baseline Subset (SBAS) remote sensing analysis. Both techniques showed that the continuous subsidence was prevailing in the kilometer range of 13–70 of pipelines crossing two seismic faults. The ground uplift deformations were observed in the pipeline kilometer range of 0–13. Although both PS-InSAR and SBAS measurements were highly consistent in deformation patterns and trends along pipelines, they showed differences in the spatial distribution of ground deformation classes and noisiness of produced results. High dispersion of PS-InSAR measurements caused low regression coefficients with SBAS for the entire pipeline kilometer range of 0–70. SBAS showed better performance than PS-InSAR along buried petroleum and gas pipelines in the following aspects: the complete coverage of the measured points, significantly lower dispersion of the results, continuous and realistic measurements and higher accuracy of ground deformation rates against the GPS historical measurements. As a primary factor of ground deformations, the influence of tectonic movements was observed in the wide scale analysis along 70 km long and 10 km wide section of petroleum and gas pipelines; however, the largest subsidence rates were observed in the areas of agricultural activities which accelerate the deformation rates caused by the tectonic processes. The diverse spatial distribution and variation of ground movement processes along pipelines demonstrated that general geological and geotechnical understanding of the study area is not sufficient to find and mitigate all the critical sites of subsidence and uplifts for the pipeline operators. This means that both techniques outlined in this paper provide a significant improvement for ground deformation monitoring or can significantly contribute to the assessment of geohazards and preventative countermeasures along petroleum and gas pipelines. [ABSTRACT FROM AUTHOR]

The article presents the results of applying a Small Baseline Subset (SBAS) method to the monitoring of the influence of underground mining exploitation on terrain surface. Calculations were performed on the basis of two large SAR data sets. Calculations of time series additionally employed the Tymofyeyeva and Fialko empirical method for estimating atmospheric delay. A series of test calculations allowed verifying the potential of the method. The SBAS calculations were based on theoretical data prepared with the use of the Mogi model. This approach allowed simulating both underground mining exploitation and induced tremors. The results indicate that the model is useful in detecting sudden ground surface deformations. In such a situation, the image of a tremor can be observed in the atmospheric component. The actual data used in the analysis covered a region of underground copper ore extraction in southwest Poland. The calculations were based on SAR data obtained from the Sentinel 1A/B satellites, for the period between the end of 2014 and May 2018, from paths 22 and 73. In both cases, the total number of images exceeded 120. They served to calculate over 420 interferograms for each set. The results of ground surface displacements allowed precise identification of areas affected by underground mining activity. Over the acquisition period of six days, sufficient amount of SAR data was obtained to precisely monitor surface changes in the analyzed area. The employed empirical atmospheric delay reduction method was demonstrated to enable the detection of sudden ground surface changes due to mining tremors. This feature makes the method useful in detecting induced seismic events in areas characterized by intensive mining activity. It allows determining tremor locations in cases when acquisition dates are greater than the optimal value of 6–12 days (in the case of Sentinel 1A/B). [ABSTRACT FROM AUTHOR]