Advanced exploitation of Sentinel-1 data for supporting landslide risk analysis

Tesi en modalitat de compendi de publicacionsSatellite Synthetic Aperture Radar Interferometry (InSAR) and Persistent Scatterer Interferometry (PSI) are now consolidated tools for ground movement detection and monitoring. Sentinel-1 (S1) is the first satellite providing free data access and ensuring a regular acquisition worldwide, every 6 days, increasing its potential for long-term monitoring applications. Several regional and national ground motion services are already active, providing products based on S1 data. Soon in 2022 the first European Ground Motion Service (EGMS) will be available and freely provide a displacement map over the whole Europe, with annual updates. This implies a strong expansion of availability of PSI-based displacement maps and an easy access for anyone, with an increasing interest among a wider range of users, including public or governmental institutions, academia, industry, and citizens. The analysis and interpretation of this amount of data is difficult and time consuming, mostly for non-expert InSAR users. The objective of this work is developing methodologies to simplify the operational use of PSI displacement maps, generating derived products with a clear message, easy-to-interpret, and fast to read. We propose a method to be applied over regional scale PSI displacement maps, to fast detect the most significant Active Deformation Areas (ADAs). The ADA map is a first product that allows a fast focusing on the active areas, to prioritize further analysis and investigation. Starting from the ADAs, the potential phenomena are attributed to each area through a preliminary interpretation based on auxiliary data, to derive the Geohazard Activity Map. In this work, a methodology to include the ADA information in the Civil Protection Activities is proposed, with the main output called Vulnerable Elements Activity Maps (VEAM). An application of the VEAM is illustrated in the Canary Islands. Furthermore, the ADA map is used in the Valle d'Aosta Region (Northern of Italy) to generate vulnerability and potential loss maps. Finally, a methodology to derive potential damage maps of the exposed buildings, based on the spatial gradients of movement, is proposed, and applied in a coastal area of the Province of Granada (Spain). A pack of software tools has been developed based on the proposed methods to extract ADA and then classify them to generate a Geohazard Activity Map. The set of tools is called ADATools, it is open-access, easy to use and fast, improving the operational exploitation of PSI regional-scale displacement maps. All the methodologies have been developed in the frame of several European projects (Safety, U-Geohaz, MOMIT and RISKCOAST), and are aimed at supporting the multi-scale territorial management and risk analysis activities, with a specific focus on landslides.La interferometría satelital radar (InSAR) y la interferometría de dispersores persistentes (PSI) son herramientas consolidadas para la detección y el monitoreo de movimientos de la superficie de la Tierra. Sentinel-1 (S1) es el primer satélite que proporciona acceso gratuito a los datos y garantiza una adquisición regular en todo el mundo, cada 6 días, aumentando su potencial para aplicaciones de monitoreo a largo plazo. Varios Ground Motion Services regionales y nacionales ya están activos, proporcionando productos basados en datos S1. Pronto, en 2022, el primer servicio europeo (European Ground Motion Service - EGMS) estará disponible y facilitará libremente un mapa de movimientos de toda Europa, con actualizaciones anuales. Esto implica un aumento de la disponibilidad de mapas de movimientos basados en PSI y un fácil acceso para cualquier persona, con un interés creciente entre una amplia gama de usuarios, incluyendo instituciones públicas o gubernamentales, academias, industrias y ciudadanos. El análisis e interpretación de esta cantidad de datos es difícil y consume mucho tiempo, mayormente para usuarios no expertos en la técnica. El objetivo de este trabajo es desarrollar metodologías para simplificar el uso operativo de los mapas de desplazamiento PSI, generando productos derivados con un mensaje claro, fácil de interpretar, y rápido de leer. Se propone un método para detectar rápidamente las Áreas de Deformación Activas (ADAs) más significativas, a partir de mapas de desplazamiento PSI de escala regional. El mapa de las ADAs es un primer producto que permite un enfoque rápido en las áreas activas, útil para priorizar el análisis y las investigaciones adicionales. A partir de las ADAs, se propone una interpretación preliminar basada en datos auxiliares, que atribuye a cada área el fenómeno que está detrás del movimiento, generando el Geohazard Activity Map (GAM). Después, se propone una metodología para incluir la información de las ADAs en las actividades de protección civil, generando los Vulnerable Element Activity Maps (VEAM), a través de su aplicación en las Islas Canarias. Además, el mapa de las ADAs se utiliza en la región de Valle D'Aosta (norte de Italia) para generar mapas de vulnerabilidad y posibles pérdidas económicas. Finalmente, se propone una metodología para obtener mapas de daños potenciales de los edificios expuestos, basados en los gradientes espaciales de movimiento, y se aplica en un área costera de la provincia de Granada (España). A partir de los métodos propuestos para extraer y clasificar las ADAs, y de otros métodos de análisis existentes, se ha desarrollado un paquete de herramientas, los ADAtools, de acceso abierto, fáciles de usar y rápidas, que optimizan la explotación operativa de los mapas de desplazamiento de escala regional. Todas las metodologías se han desarrollado en el marco de varios proyectos europeos (Safety, U-Geohaz, MOMIT y RISKCOAST), y están dirigidos a apoyar las actividades de gestión territorial y análisis de riesgos, con un enfoque específico a los deslizamientos de tierra.Postprint (published version

Advanced exploitation of Sentinel-1 data for supporting landslide risk analysis

Tesi en modalitat de compendi de publicacionsSatellite Synthetic Aperture Radar Interferometry (InSAR) and Persistent Scatterer Interferometry (PSI) are now consolidated tools for ground movement detection and monitoring. Sentinel-1 (S1) is the first satellite providing free data access and ensuring a regular acquisition worldwide, every 6 days, increasing its potential for long-term monitoring applications. Several regional and national ground motion services are already active, providing products based on S1 data. Soon in 2022 the first European Ground Motion Service (EGMS) will be available and freely provide a displacement map over the whole Europe, with annual updates. This implies a strong expansion of availability of PSI-based displacement maps and an easy access for anyone, with an increasing interest among a wider range of users, including public or governmental institutions, academia, industry, and citizens. The analysis and interpretation of this amount of data is difficult and time consuming, mostly for non-expert InSAR users. The objective of this work is developing methodologies to simplify the operational use of PSI displacement maps, generating derived products with a clear message, easy-to-interpret, and fast to read. We propose a method to be applied over regional scale PSI displacement maps, to fast detect the most significant Active Deformation Areas (ADAs). The ADA map is a first product that allows a fast focusing on the active areas, to prioritize further analysis and investigation. Starting from the ADAs, the potential phenomena are attributed to each area through a preliminary interpretation based on auxiliary data, to derive the Geohazard Activity Map. In this work, a methodology to include the ADA information in the Civil Protection Activities is proposed, with the main output called Vulnerable Elements Activity Maps (VEAM). An application of the VEAM is illustrated in the Canary Islands. Furthermore, the ADA map is used in the Valle d'Aosta Region (Northern of Italy) to generate vulnerability and potential loss maps. Finally, a methodology to derive potential damage maps of the exposed buildings, based on the spatial gradients of movement, is proposed, and applied in a coastal area of the Province of Granada (Spain). A pack of software tools has been developed based on the proposed methods to extract ADA and then classify them to generate a Geohazard Activity Map. The set of tools is called ADATools, it is open-access, easy to use and fast, improving the operational exploitation of PSI regional-scale displacement maps. All the methodologies have been developed in the frame of several European projects (Safety, U-Geohaz, MOMIT and RISKCOAST), and are aimed at supporting the multi-scale territorial management and risk analysis activities, with a specific focus on landslides.La interferometría satelital radar (InSAR) y la interferometría de dispersores persistentes (PSI) son herramientas consolidadas para la detección y el monitoreo de movimientos de la superficie de la Tierra. Sentinel-1 (S1) es el primer satélite que proporciona acceso gratuito a los datos y garantiza una adquisición regular en todo el mundo, cada 6 días, aumentando su potencial para aplicaciones de monitoreo a largo plazo. Varios Ground Motion Services regionales y nacionales ya están activos, proporcionando productos basados en datos S1. Pronto, en 2022, el primer servicio europeo (European Ground Motion Service - EGMS) estará disponible y facilitará libremente un mapa de movimientos de toda Europa, con actualizaciones anuales. Esto implica un aumento de la disponibilidad de mapas de movimientos basados en PSI y un fácil acceso para cualquier persona, con un interés creciente entre una amplia gama de usuarios, incluyendo instituciones públicas o gubernamentales, academias, industrias y ciudadanos. El análisis e interpretación de esta cantidad de datos es difícil y consume mucho tiempo, mayormente para usuarios no expertos en la técnica. El objetivo de este trabajo es desarrollar metodologías para simplificar el uso operativo de los mapas de desplazamiento PSI, generando productos derivados con un mensaje claro, fácil de interpretar, y rápido de leer. Se propone un método para detectar rápidamente las Áreas de Deformación Activas (ADAs) más significativas, a partir de mapas de desplazamiento PSI de escala regional. El mapa de las ADAs es un primer producto que permite un enfoque rápido en las áreas activas, útil para priorizar el análisis y las investigaciones adicionales. A partir de las ADAs, se propone una interpretación preliminar basada en datos auxiliares, que atribuye a cada área el fenómeno que está detrás del movimiento, generando el Geohazard Activity Map (GAM). Después, se propone una metodología para incluir la información de las ADAs en las actividades de protección civil, generando los Vulnerable Element Activity Maps (VEAM), a través de su aplicación en las Islas Canarias. Además, el mapa de las ADAs se utiliza en la región de Valle D'Aosta (norte de Italia) para generar mapas de vulnerabilidad y posibles pérdidas económicas. Finalmente, se propone una metodología para obtener mapas de daños potenciales de los edificios expuestos, basados en los gradientes espaciales de movimiento, y se aplica en un área costera de la provincia de Granada (España). A partir de los métodos propuestos para extraer y clasificar las ADAs, y de otros métodos de análisis existentes, se ha desarrollado un paquete de herramientas, los ADAtools, de acceso abierto, fáciles de usar y rápidas, que optimizan la explotación operativa de los mapas de desplazamiento de escala regional. Todas las metodologías se han desarrollado en el marco de varios proyectos europeos (Safety, U-Geohaz, MOMIT y RISKCOAST), y están dirigidos a apoyar las actividades de gestión territorial y análisis de riesgos, con un enfoque específico a los deslizamientos de tierra.Enginyeria del terren

Ground-based synthetic aperture radar (GBSAR) interferometry for deformation monitoring

Ph. D ThesisGround-based synthetic aperture radar (GBSAR), together with interferometry, represents a powerful tool for deformation monitoring. GBSAR has inherent flexibility, allowing data to be collected with adjustable temporal resolutions through either continuous or discontinuous mode. The goal of this research is to develop a framework to effectively utilise GBSAR for deformation monitoring in both modes, with the emphasis on accuracy, robustness, and real-time capability. To achieve this goal, advanced Interferometric SAR (InSAR) processing algorithms have been proposed to address existing issues in conventional interferometry for GBSAR deformation monitoring. The proposed interferometric algorithms include a new non-local method for the accurate estimation of coherence and interferometric phase, a new approach to selecting coherent pixels with the aim of maximising the density of selected pixels and optimizing the reliability of time series analysis, and a rigorous model for the correction of atmospheric and repositioning errors. On the basis of these algorithms, two complete interferometric processing chains have been developed: one for continuous and the other for discontinuous GBSAR deformation monitoring. The continuous chain is able to process infinite incoming images in real time and extract the evolution of surface movements through temporally coherent pixels. The discontinuous chain integrates additional automatic coregistration of images and correction of repositioning errors between different campaigns. Successful deformation monitoring applications have been completed, including three continuous (a dune, a bridge, and a coastal cliff) and one discontinuous (a hillside), which have demonstrated the feasibility and effectiveness of the presented algorithms and chains for high-accuracy GBSAR interferometric measurement. Significant deformation signals were detected from the three continuous applications and no deformation from the discontinuous. The achieved results are justified quantitatively via a defined precision indicator for the time series estimation and validated qualitatively via a priori knowledge of these observing sites.China Scholarship Council (CSC), Newcastle Universit

Monitoring activity at the Daguangbao mega-landslide (China) using Sentinel-1 TOPS time series interferometry

The Daguangbao mega-landslide (China), induced by the 2008 Wenchuan earthquake (Mw = 7.9), with an area of approximately 8 km2, is one of the largest landslides in the world. Experts predicted that the potential risk and instability of the landslide might remain for many decades, or even longer. Monitoring the activity of such a large landslide is hence critical. Terrain Observation by Progressive Scans (TOPS) mode from the Sentinel-1 satellite provides us with up-to-date high-quality Synthetic Aperture Radar (SAR) images over a wide ground coverage (250 × 250 km), enabling full exploitation of various InSAR applications. However, the TOPS mode introduces azimuth-dependent Doppler variations to radar signals, which requires an additional processing step especially for SAR interferometry. Sentinel-1 TOPS data have been widely applied to earthquakes, but the performance of TOPS data-based time series analysis requires further exploitation. In this study, Sentinel-1 TOPS data were employed to investigate landslide post-seismic activities for the first time. To deal with the azimuth-dependent Doppler variations, a processing chain of TOPS time series interferometry approach was developed. Since the Daguangbao landslide is as a result of the collapse of a whole mountain caused by the 2008 Mw 7.9 Wenchuan earthquake, the existing Digital Elevation Models (DEMs, e.g. SRTM and ASTER) exhibit height differences of up to approximately 500 m. Tandem-X images acquired after the earthquake were used to generate a high resolution post-seismic DEM. The high gradient topographic errors of the SRTM DEM (i.e. the differences between the pre-seismic SRTM and the actual post-seismic elevation), together with low coherence in mountainous areas make it difficult to derive a precise DEM using the traditional InSAR processing procedure. A re-flattening iterative method was hence developed to generate a precise TanDEM-X DEM in this study. The volume of the coseismic Daguangbao landslide was estimated to be of 1.189 ± 0.110 × 109 m3 by comparing the postseismic Tandem-X DEM with the preseismic SRTM DEM, which is consistent with the engineering geological survey result. The time-series results from Sentinel-1 show that some sectors of the Daguangbao landslide are still active (and displaying four sliding zones) and exhibiting a maximum displacement rate of 8 cm/year, even eight years after the Wenchuan earthquake. The good performance of TOPS in this time series analysis indicates that up-to-date high-quality TOPS data with spatiotemporal baselines offer significant potential in terms of future InSAR applications.This work was supported by the National Natural Science Foundation of China under Grant No. 41474003. The research stay of Dr. Tomás at Newcastle University was funded by the Ministry of Education, Culture and Sport within the framework of Project PRX14/00100. Additional funding was obtained from the Spanish Government under projects TIN2014-55413-C2-2-P and ESP2013-47780-C2-2-R. Part of this work is also supported by the UK Natural Environmental Research Council (NERC) through the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET, ref.: come30001) and the LICS and CEDRRiC projects (ref. NE/K010794/1 and NE/N012151/1, respectively), the ESA-MOST DRAGON-3 projects (ref. 10607 and 10665), the ESA-MOST DRAGON-4 project (ref. 32244) and the Open Fund from the Key Laboratory of Earth Fissures Geological Disaster, Ministry of Land and Resources (ref.: gla2013001)

Displacements Monitoring over Czechia by IT4S1 System for Automatised Interferometric Measurements Using Sentinel-1 Data

The Sentinel-1 satellite system continuously observes European countries at a relatively high revisit frequency of six days per orbital track. Given the Sentinel-1 configuration, most areas in Czechia are observed every 1–2 days by different tracks in a moderate resolution. This is attractive for various types of analyses by various research groups. The starting point for interferometric (InSAR) processing is an original data provided in a Single Look Complex (SLC) level. This work represents advantages of storing data augmented to a specifically corrected level of data, SLC-C. The presented database contains Czech nationwide Sentinel-1 data stored in burst units that have been pre-processed to the state of a consistent well-coregistered dataset of SLC-C. These are resampled SLC data with their phase values reduced by a topographic phase signature, ready for fast interferometric analyses (an interferogram is generated by a complex conjugate between two stored SLC-C files). The data can be used directly into multitemporal interferometry techniques, e.g., Persistent Scatterers (PS) or Small Baseline (SB) techniques applied here. A further development of the nationwide system utilising SLC-C data would lead into a dynamic state where every new pre-processed burst triggers a processing update to detect unexpected changes from InSAR time series and therefore provides a signal for early warning against a potential dangerous displacement, e.g., a landslide, instability of an engineering structure or a formation of a sinkhole. An update of the processing chain would also allow use of cross-polarised Sentinel-1 data, needed for polarimetric analyses. The current system is running at a national supercomputing centre IT4Innovations in interconnection to the Czech Copernicus Collaborative Ground Segment (CESNET), providing fast on-demand InSAR results over Czech territories. A full nationwide PS processing using data over Czechia was performed in 2017, discovering several areas of land deformation. Its downsampled version and basic findings are demonstrated within the article

Elevation and Deformation Extraction from TomoSAR

3D SAR tomography (TomoSAR) and 4D SAR differential tomography (Diff-TomoSAR) exploit multi-baseline SAR data stacks to provide an essential innovation of SAR Interferometry for many applications, sensing complex scenes with multiple scatterers mapped into the same SAR pixel cell. However, these are still influenced by DEM uncertainty, temporal decorrelation, orbital, tropospheric and ionospheric phase distortion and height blurring. In this thesis, these techniques are explored. As part of this exploration, the systematic procedures for DEM generation, DEM quality assessment, DEM quality improvement and DEM applications are first studied. Besides, this thesis focuses on the whole cycle of systematic methods for 3D & 4D TomoSAR imaging for height and deformation retrieval, from the problem formation phase, through the development of methods to testing on real SAR data. After DEM generation introduction from spaceborne bistatic InSAR (TanDEM-X) and airborne photogrammetry (Bluesky), a new DEM co-registration method with line feature validation (river network line, ridgeline, valley line, crater boundary feature and so on) is developed and demonstrated to assist the study of a wide area DEM data quality. This DEM co-registration method aligns two DEMs irrespective of the linear distortion model, which improves the quality of DEM vertical comparison accuracy significantly and is suitable and helpful for DEM quality assessment. A systematic TomoSAR algorithm and method have been established, tested, analysed and demonstrated for various applications (urban buildings, bridges, dams) to achieve better 3D & 4D tomographic SAR imaging results. These include applying Cosmo-Skymed X band single-polarisation data over the Zipingpu dam, Dujiangyan, Sichuan, China, to map topography; and using ALOS L band data in the San Francisco Bay region to map urban building and bridge. A new ionospheric correction method based on the tile method employing IGS TEC data, a split-spectrum and an ionospheric model via least squares are developed to correct ionospheric distortion to improve the accuracy of 3D & 4D tomographic SAR imaging. Meanwhile, a pixel by pixel orbit baseline estimation method is developed to address the research gaps of baseline estimation for 3D & 4D spaceborne SAR tomography imaging. Moreover, a SAR tomography imaging algorithm and a differential tomography four-dimensional SAR imaging algorithm based on compressive sensing, SAR interferometry phase (InSAR) calibration reference to DEM with DEM error correction, a new phase error calibration and compensation algorithm, based on PS, SVD, PGA, weighted least squares and minimum entropy, are developed to obtain accurate 3D & 4D tomographic SAR imaging results. The new baseline estimation method and consequent TomoSAR processing results showed that an accurate baseline estimation is essential to build up the TomoSAR model. After baseline estimation, phase calibration experiments (via FFT and Capon method) indicate that a phase calibration step is indispensable for TomoSAR imaging, which eventually influences the inversion results. A super-resolution reconstruction CS based study demonstrates X band data with the CS method does not fit for forest reconstruction but works for reconstruction of large civil engineering structures such as dams and urban buildings. Meanwhile, the L band data with FFT, Capon and the CS method are shown to work for the reconstruction of large manmade structures (such as bridges) and urban buildings

Post-disaster assessment of 2017 catastrophic Xinmo landslide (China) by spaceborne SAR interferometry

Timely and effective post-disaster assessment is of significance for the design of rescue plan, taking disaster mitigation measures and disaster analysis. Field investigation and remote sensing methods are the common ways to perform post-disaster assessment, which are usually limited by dense cloud coverage, potential risk, and tough transportation etc. in the mountainous area. In this paper, we employ the 2017 catastrophic Xinmo landslide (Sichuan, China) to demonstrate the feasibility of using spaceborne synthetic aperture radar (SAR) data to perform timely and effective post-disaster assessment. With C-band Sentinel-1 data, we propose to combine interferometric coherence to recognize the stable area, which helps us successfully identify landslide source area and boundaries in a space-based remote sensing way. Complementarily, X-band TanDEM-X SAR data allow us to generate a precise pre-failure high-resolution digital elevation model (DEM), which provides us the ability to accurately estimate the depletion volume and accumulation volume of Xinmo landslide. The results prove that spaceborne SAR can provide a quick, valuable, and unique assistance for post-disaster assessment of landslides from a space remote sensing way. At some conditions (bad weather, clouds, etc.), it can provide reliable alternative.This work was funded by Sichuan Science and Technology Plan Key Research and Development Program (Grant No. 2018SZ0339), National Natural Science Foundation of China (Grant No. 41801391), State Key Laboratory of Geodesy and Earth’s Dynamics Open fund (Grant No. SKLGED2018-5-3-E), The Funds for Creative Research Groups of China (Grant No. 41521002) and partially supported by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO), the State Agency of Research (AEI), and European Funds for Regional Development (FEDER), under project TIN2014-55413-C2-2-P and by the Spanish Ministry of Education, Culture and Sport, under project PRX17/00439. This work was also supported by the National Environment Research Council (NERC) through the Centre for the Observation and Modeling of Earthquakes, Volcanoes and Tectonics (COMET, ref.: come30001), the LiCS project (ref. NE/K010794/1), the ESA-MOST DRAGON-4 project (ref. 32244), and the Hunan Province Key Laboratory of Coal Resources Clean-Utilization and Mine Environment Protection, Hunan University of Science and Technology (Ref. E21608)

Complex Surface Displacements above the Storage Cavern Field at Epe, NW-Germany, Observed by Multi-Temporal SAR-Interferometry

The storage cavern field at Epe has been brined out of a salt deposit belonging to the lower Rhine salt flat, which extends under the surface of the North German lowlands and part of the Netherlands. Cavern convergence and operational pressure changes cause surface displacements that have been studied for this work with the help of SAR interferometry (InSAR) using distributed and persistent scatterers. Vertical and East-West movements have been determined based on Sentinel-1 data from ascending and descending orbit. Simple geophysical modeling is used to support InSAR processing and helps to interpret the observations. In particular, an approach is presented that allows to relate the deposit pressures with the observed surface displacements. Seasonal movements occurring over a fen situated over the western part of the storage site further complicate the analysis. Findings are validated with ground truth from levelling and groundwater level measurements