Differential SAR Interferometry Technique Research Articles

Integration of DInSAR and SBAS radar techniques to delineate the main areas of river recharge by sediments using ALOS-PALSAR-2 data: Oued Ghis case in Morocco

The Rif mountain range in northern Morocco comprises vulnerable lands highly susceptible to erosion, particularly water-induced erosion. This phenomenon significantly impacts the long-term sustainability of soil and water resources, including the lifespan of dam reservoirs and aquifer replenishment. Given that soil degradation is often accompanied by the transfer and accumulation of sediments over time in surface watercourses, monitoring this process using Differential Synthetic Aperture Radar Interferometry (DInSAR) provides insights into surface deformation. Integrating DInSAR techniques with the Small Baseline Subset (SBAS) approach using ALOS-PALSAR data enables the retrieval of a comprehensive deformation model over the study area. The results highlight the primary sources of erosion and sediment deposition zones. Displacement rates can reach up to 10 cm/year. Evaluation against ground truth data demonstrates that erosion and deposition rates are influenced by geological characteristics, rock mechanical properties, and topography. The good agreement between SBAS and DInSAR suggests that the SBAS technique could be reliable for identifying sediment recharge zones in these areas

On the DInSAR technique for the structural monitoring of modern existing bridges

The setting up of efficient strategies for safety assessments and maintenance of modern existing bridges is a crucial research challenge in structural engineering. In Italy, this topic has recently been addressed in guidelines issued by the Ministry of Infrastructures and Transport in 2020. The guidelines outline procedures and tools for safety assessments and maintenance interventions: a mandatory step is the analysis of original documents (concerning the design, the construction process and the maintenance interventions) in order to acquire robust knowledge of the structure. As noted in recent works in the literature, non-invasive structural monitoring approaches play a crucial role in the safety assessment of existing bridges. One such approach is multi-temporal differential synthetic aperture radar interferometry (DInSAR). This paper presents a cross-disciplinary process for the structural monitoring of modern existing bridges, based on integration of DInSAR measurements, exploiting Cosmo-SkyMed measurements collected during the period 2011–2019, and accurate knowledge of the structures derived from analysis of original documents conserved in historical archives. The procedure is applied to two reinforced concrete Gerber bridges in Rome, designed in the 1930s.

Retrieval of Svalbard ice flow velocities using Sentinel 1A/1B three-pass Differential SAR Interferometry

Glacier velocity is an important parameter to characterize glacier dynamics and to derive ice thickness and mass balance. The 2-pass/3-pass Differential Synthetic Aperture Radar Interferometry (DInSAR) techniques are advantageous in estimating glacier movements. However, the 2-pass DInSAR requires an external Digital Elevation Model (DEM), whereas the 3-pass DInSAR does not. The 3-pass DInSAR technique is adopted with Sentinel-1A/1B to map the Svalbard glacier flow velocities. Furthermore, the effect of glacier surface elevation change on the 2-pass DInSAR results were revealed by comparing glacier velocity with the two time period topographic information. The coherence indicates that Sentinel-1A/1B has a high potential to infer operational glacier velocity using the 3-pass DInSAR method with an average atmospheric uncertainty of 0.24 cm/day over the studied region. The precision of the 3-pass DInSAR is analyzed by comparing 2-pass derived line-of-sight (LOS) velocity on the same dates. The 3-pass DInSAR achieves high-resolution and detailed information.

InSAR as a tool for monitoring hydropower projects: A review

This paper provides a review of using Interferometric Synthetic Aperture Radar (InSAR), a microwave remote sensing technique, for deformation monitoring of hydroelectric power projects, a critical infrastructure that requires consistent and reliable monitoring. Almost all major dams around the world were built for the generation of hydropower. InSAR can enhance dam safety by providing timely settlement measurements at high spatial-resolution. This paper provides a holistic view of different InSAR deformation monitoring techniques such as Differential Synthetic Aperture Radar Interferometry (DInSAR), Ground-Based Synthetic Aperture Radar (GBInSAR), Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR), Multi-Temporal Interferometric Synthetic Aperture Radar (MTInSAR), Quasi-Persistent Scatterer Interferometric Synthetic Aperture Radar (QPSInSAR) and Small BAseline Subset (SBAS). PSInSAR, GBInSAR, MTInSAR, and DInSAR techniques were quite commonly used for deformation studies. These studies demonstrate the advantage of InSAR-based techniques over other conventional methods, which are laborious, costly, and sometimes unachievable. InSAR technology is also favoured for its capability to provide monitoring data at all times of day or night, in all-weather conditions, and particularly for wide areas with mm-scale precision. However, the method also has some disadvantages, such as the maximum deformation rate that can be monitored, and the location for monitoring cannot be dictated. Through this review, we aim to popularize InSAR technology to monitor the deformation of dams, which can also be used as an early warning method to prevent any unprecedented catastrophe. This study also discusses some case studies from southern India to demonstrate the capabilities of InSAR to indirectly monitor dam health.

Satellite radar interferometry: Potential and limitations for structural assessment and monitoring

The present paper analyzes potential and limitations of multi-temporal Differential Synthetic Aperture Radar Interferometry (DInSAR) techniques applied for the structural monitoring and assessment of constructions affected by different external actions. A comprehensive approach for the processing, interpretation and proper use of satellite radar interferometry data for structural analyses at urban and single-construction scales is proposed. Following a brief literature review, highlighting the most relevant applications in this field, some aspects concerning DInSAR techniques are shortly summarized, particularly focusing on the Small BAseline Subset (SBAS) approach applied to perform advanced analyses at structural level. Then, the main issues of the DInSAR measurements exploitation for structural applications are discussed, focusing on the use of both one or two datasets relevant to ascending and descending satellite passes. Analysis at the scale of single construction (i.e., building, bridge, etc.) of displacements time series and mean deformation velocities is discussed, in order to identify scenarios that may become potentially critical for the structures. Some application examples are provided, employing COSMO-SkyMed (CSK) datasets relative to the urban area of Rome (Italy), acquired during the 2011–2019 time interval and processed through the SBAS algorithm. Specific considerations related to the use of DInSAR measurements for structural monitoring and assessment are then proposed, also discussing possible approaches for preliminary and detailed evaluation of structural damages.

Drone-borne Differential SAR Interferometry

Differential synthetic aperture radar interferometry (DInSAR) has been widely applied since the pioneering space-borne experiment in 1989, and subsequently with the launch of the ERS-1 program in 1992. The DInSAR technique is well assessed in the case of space-borne SAR data, whereas in the case of data acquired from aerial platforms, such as airplanes, helicopters, and drones, the effective application of this technique is still a challenging task, mainly due to the limited accuracy of the information provided by the navigation systems mounted onboard the platforms. The first airborne DInSAR results for measuring ground displacement appeared in 2003 using L- and X-bands. DInSAR displacement results with long correlation time in P-band were published in 2011. This letter presents a SAR system and, to the best of our knowledge, the first accuracy assessment of the DInSAR technique using a drone-borne SAR in L-band. A deformation map is shown, and the accuracy and resolution of the methodology are presented and discussed. In particular, we have obtained an accuracy better than 1 cm for the measurement of the observed ground displacement. It is in the same order as that achieved with space-borne systems in C- and X-bands and the airborne systems in X-band. However, compared to these systems, we use here a much longer wavelength. Moreover, compared to the satellite experiments available in the literature and aimed at assessing the accuracy of the DInSAR technique, we use only two flight tracks with low time decorrelation effects and not a big data stack, which helps in reducing the atmospheric effects.

Synergic Use of Multi-Sensor Satellite Data for Volcanic Hazards Monitoring: The Fogo (Cape Verde) 2014–2015 Effusive Eruption

Monitoring and retrieving information of volcanic eruptions are important tasks for assessing the hazard and its evolution in time. Satellite remote sensing data are nowadays suitable tools to perform such tasks, thanks to their capability to access disastrous event also in remote and under-monitored regions, with frequent revisit time and accurate spatial information. In this work, we have analyzed satellite images, coming from both Synthetic Aperture Radar (SAR) and Optical sensors, to characterize the 2014-2015 eruption of Fogo volcano, Cape Verde. In particular, we have exploited images collected by the European Space Agency (ESA) Sentinel-1, the Italian Space Agency (ASI) COSMO-SkyMed, and NASA/USGS Landsat-8 and Earth-Observing-1 missions, for studying the lava emplacement and volcanic source of the eruption that took place between November 2014 and January 2015. On one side, we have adopted a new automatic change detection technique for estimating the lava field and its temporal evolution, taking advantage of the intensity and the Interferometric SAR coherence. The two SAR-based features were combined using an innovative algorithm able to take full advantage of the Sentinel-1 mission’s six-day repeat cycle, thereby providing an unprecedented possibility to fully exploit the multi-temporal InSAR coherence to detect surface changes. On the other side, we have exploited the consolidated differential SAR interferometry technique to map the ground deformation and retrieve the feeding dyke by inverting syn-eruptive data. The proposed methods based on change detection for the estimation of the lava flow is capable of resolving with spatial and temporal detail the evolution of lava flows. Results from source modelling from the SAR data show a SW-NE oriented dyke, located inside Cha das Caldeiras, SW of the Pico do Fogo. The work suggests a multidisciplinary and multi-sensor approach, highlighting the benefits and limitations of satellite data and image processing techniques in an operational environment.

Integration of DInSAR and SBAS Techniques to Determine Mining-Related Deformations Using Sentinel-1 Data: The Case Study of Rydułtowy Mine in Poland

Underground coal exploitation often results in land-surface subsidence, the rate of which depends on geological characteristics, the mechanical properties of the rocks, and the applied extraction technology. Since mining-related subsidence is characterized by “fast” displacement and high nonlinearity, monitoring this process by using Interferometric Synthetic Aperture Radar (InSAR) is very challenging. The Small BAseline Subset (SBAS) approach needs to predefine an a priori deformation model to properly estimate an interferometric component related to displacements. As a consequence, there is a lack of distributed scatterers (DS) when the selected a priori deformation model deviates from the real deformation. The conventional differential SAR interferometry (DInSAR) approach does not have this limitation, since it does not need any deformation model. However, the accuracy of this technique is limited by factors related to spatial and temporal decorrelation, signal delays due to the atmospheric artifacts, and orbital or topographic errors. Therefore, this study presents the integration of DInSAR and SBAS techniques in order to leverage the advantages and overcome the disadvantages of both methods and to retrieve the complete deformation pattern over the investigated study area. The obtained results were evaluated internally and externally with leveling data. Results indicated that the Kriging-based integration method of DInSAR and SBAS can be effectively applied to monitor mining-related subsidence. The root-mean-square Error (RMSE) between modeled and measured deformation by InSAR was found to be 11 and 13 mm for vertical and horizontal displacements, respectively. Moreover, DInSAR technique as a cost-effective and complementary method to conventional geodetic techniques can be applied for effective monitoring fast mining subsidence. The minimum and maximum RMSE between DInSAR displacement and specific leveling profiles were found to be 0.9 and 3.2 cm, respectively. Since the SBAS processing failed in subsidence estimation in the area of maximum deformation rate, the deformation estimates outside the maximum rate could only be compared. In these areas, the good agreement between SBAS and DInSAR indicates that the SBAS technique could be reliable for monitoring the residual subsidence that surrounds the subsidence trough. Using the proposed approach, we detected subsidence of up to −1 m and planar displacements (east–west) of up to 0.24 m.

Comparing DInSAR and PSI Techniques Employed to Sentinel-1 Data to Monitor Highway Stability: A Case Study of a Massive Dobkovičky Landslide, Czech Republic

Single-pair differential synthetic aperture radar interferometry (DInSAR) as well as more advanced methods, such as persistent scatterer interferometry (PSI), allow vertical displacements to be detected at the sub-centimeter level. Since 2014 free SAR data—Sentinel-1—have been collected systematically under the COPERNICUS program at a high temporal resolution and with global coverage. Such an open-access policy greatly helps build a wide user-community and develop diverse SAR-based applications. In this study conventional single-pair DInSAR and the PSI techniques were employed to monitor the vertical displacements of the newly constructed D8 highway, more specifically the part passing through the České Středohoří Mountains, where, during highway construction, a massive landslide occurred in June 2013. For both DInSAR and PSI, free Sentinel-1 radar data were used; moreover, the conventional single-pair DInSAR workflow was processed using freely available SNAP software. Results from the radar interferometry were validated using in situ techniques, such as geodetic measurements, 3D inclinometers, and laser scanning. Both approaches proved their ability to achieve reliable results in detecting vertical displacement “hotspots”. Additionally, in terms of absolute values, the PSI interferometry corresponds very well with the in situ measurements. This study also shows that open-source solutions (free data and SW) provided under the COPERNICUS program bring a great potential for monitoring vertical displacements.

Application of DInSAR Technique to High Coherence Sentinel-1 Images for Dam Monitoring and Result Validation Through In Situ Measurements

Dam monitoring represents a crucial issue in order to avoid catastrophic failures due to infrastructure aging or earthquake damages. Differential SAR Interferometry (DInSAR) is a technique suitable for critical infrastructure monitoring, also for the availability of free data and tools, that can be used by experts in SAR remote sensing and also by geologists and civil engineers, after having acquired the right confidence and experience in these data processing and tool use. In order to apply the DInSAR technique, in its basic and simple version, to critical infrastructure monitoring, it is very important to assess its performance. Nevertheless, validation results are not largely available in literature, because heterogeneous technical competencies are required to this aim and in situ measurements must be collected and made available. In this paper, we propose a highly reproducible DInSAR workflow that can be effectively used for dam monitoring, by validating its results with in situ measurements on some significant case studies in Italy.

OPTIMUM CONDITIONS FOR DIFFERENTIAL SAR INTERFEROMETRY TECHNIQUE TO ESTIMATE HIMALAYAN GLACIER VELOCITY

Abstract. Differential SAR Interferometry (DInSAR) is the process of differencing two Interferograms for measuring surface movement with an accuracy of millimeter range. The DInSAR process can be applied to observe glacier movement, earthquake deformations, volcanic activities and rate of subsidence or uplift caused due to the extraction of groundwater or coal. By using single pass interferometry technique we can also generate accurate DEM. In this paper, we are presenting the movement of a Chhota Shigri glacier with the help two pass DInSAR technique and mainly we concentrated on the optimum conditions for estimating glacier movement using DInSAR. We got good coherence and Interferogram fringes for L-band sensor with less temporal baseline. Therefore, we generated glacier velocity using ALOS-2 data with 14 days temporal baseline. Initially, we generated Interferogram (defo-pair) by taking 10th March 2015 image as a master and 24th March 2015 image as a slave. But this generated Interferogram also having topographic information and atmospheric errors with the displacement component. Therefore, we used SRTM DEM for removing topographic information from the Interferogram. Because we are using L-band data, results may not be affected by troposphere. Maximum glacier velocity we observed in the accumulation zone as 7.285 cm/day in the month of March and while it’s moving towards ablation zone the glacier velocity is decreasing.

Landslide Monitoring Using Multi-Temporal SAR Interferometry with Advanced Persistent Scatterers Identification Methods and Super High-Spatial Resolution TerraSAR-X Images

Landslides are one of the most common and dangerous threats in the world that generate considerable damage and economic losses. An efficient landslide monitoring tool is the Differential Synthetic Aperture Radar Interferometry (DInSAR) or Persistent Scatter Interferometry (PSI). However, landslides are usually located in mountainous areas and the area of interest can be partially or even heavily vegetated. The inherent temporal decorrelation that dramatically reduces the number of Persistent Scatters (PSs) of the scene limits in practice the application of this technique. Thus, it is crucial to be able to detect as much PSs as possible that can be usually embedded in decorrelated areas. High resolution imagery combined with efficient pixel selection methods can make possible the application of DInSAR techniques in landslide monitoring. In this paper, different strategies to identify PS Candidates (PSCs) have been employed together with 32 super high-spatial resolution (SHR) TerraSAR-X (TSX) images, staring-spotlight mode, to monitor the Canillo landslide (Andorra). The results show that advanced PSI strategies (i.e., the temporal sub-look coherence (TSC) and temporal phase coherence (TPC) methods) are able to obtain much more valid PSs than the classical amplitude dispersion (DA) method. In addition, the TPC method presents the best performance among all three full-resolution strategies employed. The SHR TSX data allows for obtaining much higher densities of PSs compared with a lower-spatial resolution SAR data set (Sentinel-1A in this study). Thanks to the huge amount of valid PSs obtained by the TPC method with SHR TSX images, the complexity of the structure of the Canillo landslide has been highlighted and three different slide units have been identified. The results of this study indicate that the TPC approach together with SHR SAR images can be a powerful tool to characterize displacement rates and extension of complex landslides in challenging areas.

Detection of Land Subsidence in Kathmandu Valley, Nepal, Using DInSAR Technique

Differential Synthetic Aperture Radar Interferometry (DInSAR) is a remote sensing technique that is capable of detecting land surface deformation with centimeter accuracy. In this research, this technique was applied to two pairs of Advanced Land Observing Satellite (ALOS) Phased Array L-band SAR (PALSAR) data to detect land subsidence in the Kathmandu valley from 2007 to 2010. The result revealed several subsidence areas towards the center of the valley ranging from a maximum of 9.9 km2 to a minimum of 1 km2 coverage with a maximum velocity of 4.8 cm/year, and a minimum velocity of 1.1 cm/year, respectively. The majority of the subsidence was observed in old settlement areas with mixed use development. The subsidence depth was found to gradually increase from the periphery towards the center in almost all detected subsidence areas. The subsidence depth was found to be in a range of 1 cm to 17 cm. It was found that the concentration of deep water extraction wells was higher in areas with higher subsidence rates. It was also found that the detected subsidence area was situated over geological formations mainly consisting of unconsolidated fine-grained sediments (silica, sand, silt, clay and silty sandy gravel), which is the major factor affecting the occurrence of land subsidence due to groundwater extraction.

CENTIMETER COSMO-SKYMED RANGE MEASUREMENTS FOR MONITORING GROUND DISPLACEMENTS

The SAR (Synthetic Aperture Radar) imagery are widely used in order to monitor displacements impacting the Earth surface and infrastructures. The main remote sensing technique to extract sub-centimeter information from SAR imagery is the Differential SAR Interferometry (DInSAR), based on the phase information only. However, it is well known that DInSAR technique may suffer for lack of coherence among the considered stack of images. New Earth observation SAR satellite sensors, as COSMO-SkyMed, TerraSAR-X, and the coming PAZ, can acquire imagery with high amplitude resolutions too, up to few decimeters. Thanks to this feature, and to the on board dual frequency GPS receivers, allowing orbits determination with an accuracy at few centimetres level, the it was proven by different groups that TerraSAR-X imagery offer the capability to achieve, in a global reference frame, 3D positioning accuracies in the decimeter range and even better just exploiting the slant-range measurements coming from the amplitude information, provided proper corrections of all the involved geophysical phenomena are carefully applied. The core of this work is to test this methodology on COSMO-SkyMed data acquired over the Corvara area (Bolzano – Northern Italy), where, currently, a landslide with relevant yearly displacements, up to decimeters, is monitored, using GPS survey and DInSAR technique. The leading idea is to measure the distance between the satellite and a well identifiable natural or artificial Persistent Scatterer (PS), taking in account the signal propagation delays through the troposphere and ionosphere and filtering out the known geophysical effects that induce periodic and secular ground displacements. The preliminary results here presented and discussed indicate that COSMO-SkyMed Himage imagery appear able to guarantee a displacements monitoring with an accuracy of few centimetres using only the amplitude data, provided few (at least one) stable PS’s are available around the monitored area, in order to correct residual biases, likely due to orbit errors.

CENTIMETER COSMO-SKYMED RANGE MEASUREMENTS FOR MONITORING GROUND DISPLACEMENTS

Abstract. The SAR (Synthetic Aperture Radar) imagery are widely used in order to monitor displacements impacting the Earth surface and infrastructures. The main remote sensing technique to extract sub-centimeter information from SAR imagery is the Differential SAR Interferometry (DInSAR), based on the phase information only. However, it is well known that DInSAR technique may suffer for lack of coherence among the considered stack of images. New Earth observation SAR satellite sensors, as COSMO-SkyMed, TerraSAR-X, and the coming PAZ, can acquire imagery with high amplitude resolutions too, up to few decimeters. Thanks to this feature, and to the on board dual frequency GPS receivers, allowing orbits determination with an accuracy at few centimetres level, the it was proven by different groups that TerraSAR-X imagery offer the capability to achieve, in a global reference frame, 3D positioning accuracies in the decimeter range and even better just exploiting the slant-range measurements coming from the amplitude information, provided proper corrections of all the involved geophysical phenomena are carefully applied. The core of this work is to test this methodology on COSMO-SkyMed data acquired over the Corvara area (Bolzano – Northern Italy), where, currently, a landslide with relevant yearly displacements, up to decimeters, is monitored, using GPS survey and DInSAR technique. The leading idea is to measure the distance between the satellite and a well identifiable natural or artificial Persistent Scatterer (PS), taking in account the signal propagation delays through the troposphere and ionosphere and filtering out the known geophysical effects that induce periodic and secular ground displacements. The preliminary results here presented and discussed indicate that COSMO-SkyMed Himage imagery appear able to guarantee a displacements monitoring with an accuracy of few centimetres using only the amplitude data, provided few (at least one) stable PS’s are available around the monitored area, in order to correct residual biases, likely due to orbit errors.

Detection of coal-mining-induced subsidence and mapping of the resulting deformation using time series of ALOS-PALSAR data

ABSTRACTLand subsidence caused by extracted void collapses due to coal mining activities is a major geohazard in northern China. Differential SAR interferometry (DInSAR) has been adopted as an effective tool for coal mining subsidence detection and deformation mapping. However, previous studies were mostly focused on the derivation of linear deformation rates in coal mines, while the spatial–temporal pattern of coal mining subsidence and its interaction with the fault systems have rarely been investigated. In this study, ALOS-PALSAR images acquired from 19 June 2007 to 12 November 2010 were analysed with DInSAR and small baselines subset (SBAS) techniques to characterize the distribution and magnitude of subsidence in central Henan province, which is one of the leading coal producers in China. More than 40 funnel-shaped subsidence areas distributed within the coalfields have been detected in both Dengfeng and Xinmi. The maximum annual mean deformation can be as high as 8 cm in the line-of-sight (LOS) direction. Deformation maps were generated in the study area, showing an extended subsidence of 2009 compared with that of 2007. We also analysed the deformation profiles perpendicular to the faults, and found an asymmetric subsidence pattern along the profiles. Such a pattern may be an indicator of local fault activities, and it may help understanding of coal mine subsidence near faults.

Detection of mine slope motions in Brazil as revealed by satellite radar interferograms

Differential synthetic aperture radar interferometry (DInSAR) is a space-geodetic technique which allows minute surface displacements over vast areas to be detected with centimetric accuracy. Because of these unique characteristics, the DInSAR approach has great advantages over classical geodetic monitoring systems that allow the anticipation of high-risk situations. In the past few decades, it has been successfully applied in many areas of the earth and environmental sciences. However, there have been very few applications of this approach to active open pit mines in tropical environments. In this work, the DInSAR technique was applied to detect and monitor unknown surface displacements that may be occurring in the N4W iron mine, northern Brazil. X-band data acquired from March 2012 to April 2013 during the TerraSAR-X satellite mission were utilized for this purpose. The results were checked in the field and compared to optical leveling data. Due to the consistent deformation pattern observed over a mine waste pile, Pile W, we also performed numerical modeling in order to carry out a preliminary assessment of its theoretical deformation behavior. The results show that most of the study area can be considered to be stable. The numerical modeling indicated that horizontal displacements may be occurring, and that the DInSAR technique can be used to provide an initial rapid assessment of a large-scale deformation field, which could prove to be very useful, particularly in large active mining areas.

The Space-Borne SBAS-DInSAR Technique as a Supporting Tool for Sustainable Urban Policies: The Case of Istanbul Megacity, Turkey

In today’s urbanizing world, home of 28 megacities, there is a growing need for tools to assess urban policies and support the design and implementation of effective development strategies. Unsustainable practices of urbanization bring major implications for land and environment, and cause a dramatic increase of urban vulnerability to natural hazards. In Istanbul megacity, disaster risk reduction represents a challenging issue for urban managers. In this paper, we show the relevance of the space-borne Differential SAR Interferometry (DInSAR) technique as a tool for supporting risk management, and thus contributing to achieve the urban sustainability. To this aim, we use a dataset of high resolution SAR images collected by the TerraSAR-X satellite that have been processed through the advanced (multi-temporal) Small BAseline Subset (SBAS)—DInSAR technique, thus producing spatially-dense deformation velocity maps and associated time-series. Results allow to depict an up-to-date picture of surface deformations occurring in Istanbul, and thus to identify urban areas subject to potential risk. The joint analysis of remotely sensed measurements and ancillary data (geological and urban development information) provides an opportunity for city planners and land professionals to discuss on the mutual relationship between urban development policies and natural/man-made hazards.

Railway deformation detected by DInSAR over active sinkholes in the Ebro Valley evaporite karst, Spain

Abstract. Subsidence was measured for the first time on railway tracks in the central sector of Ebro Valley (NE Spain) using Differential Synthetic Aperture Radar Interferometry (DInSAR) techniques. This area is affected by evaporite karst and the analysed railway corridors traverse active sinkholes that produce deformations in these infrastructures. One of the railway tracks affected by slight settlements is the Madrid–Barcelona high-speed line, a form of transport infrastructure highly vulnerable to ground deformation processes. Our analysis based on DInSAR measurements and geomorphological surveys indicates that this line shows dissolution-induced subsidence and compaction of anthropogenic deposits (infills and embankments). Significant sinkhole-related subsidence was also measured by DInSAR techniques on the Castejón–Zaragoza conventional railway line. This study demonstrates that DInSAR velocity maps, coupled with detailed geomorphological surveys, may help in the identification of the railway track sections that are affected by active subsidence.

Modified four-pass differential SAR interferometry for estimating mountain glacier surface velocity fields

ABSTRACTConventional four-pass differential synthetic aperture radar interferometry (DInSAR) assumes that there are no significant changes in the ground during the period between the acquisition times of SAR images for topographic DInSAR pairs. This assumption can rarely be satisfied for glacial areas due to their continuous movement. This letter proposes a modified four-pass DInSAR method without an external digital elevation model (DEM), taking into account glacier movement between the acquisition times of SAR images used to form topographic DInSAR pairs. An explicit expression of theoretical formulas for a modified four-pass DInSAR technique was derived for the first time, revealing that four-pass DInSAR considering ground movement of topographic pairs was equivalent to that of conventional four-pass DInSAR with a spatially varying nominal wavelength. Then the proposed method was tested with four Advanced Land Observing Satellite (ALOS) SAR images covering Dongkemadi glacier located on the Tibetan Plateau, China. An experiment with real data showed that the proposed method could obtain glacial flow patterns efficiently, and that the difference between two-pass DInSAR and the proposed method is a result of DEM bias and glacial thinning. The approach presented in this letter proved to be appropriate for monitoring glacial motion and provides a valuable tool for glacier studies, without the need of an external DEM.