Risk-based bridge scour management:a survey

Scour is one of the major causes of bridge failure worldwide and results in significant economic losses through disruption to operation. This phenomenon naturally affects bridges with underwater foundations and is exacerbated during high river and/or turbulent flows (e.g. due to extreme events). When scour reaches the bottom or undermines shallow foundations it is likely to trigger various damage mechanisms that may in-fluence the safety of the structure and force asset managers to reduce traffic capacity. Currently, assessing risk of scour is a heuristic process, heavily reliant on qualitative approaches and expert opinion (e.g. visual inspections). These types of assessments typically suffer from insufficient knowledge of influencing factors (e.g. hydraulic parameters) and the requirement to rely on several assumptions (e.g. foundation depth). As a result, current scour assessment and bridge management practices do not provide reliable solutions for ad-dressing the potential risk of bridge failures. In this paper, cross-cutting needs and challenges related to the development of decision support tools for scour-risk management are highlighted and some preliminary re-sults of a literature survey are reported. The review has been performed with several objectives: (i) identify-ing scour-risk indicators describing hydrodynamic actions and the asset condition; (ii) defining indirect and direct consequences needed to assess the risks associated to different decision alternatives related to scour management; and (iii) identifying existing approaches to scour inspections and monitoring as support tools for informed decisions. The results of this survey will serve as a base for future research aimed to develop an informed decision support tool to manage scour risk at both the bridge and at the network level

Advanced SBAS-DInSAR technique for controlling large civil infrastructures: an application to the Genzano di Lucania dam

Monitoring surface deformation on dams is commonly carried out by in situ geodetic surveying, which is time consuming and characterized by some limitations in space coverage and frequency. More recently microwave satellite-based technologies, such as advanced-DInSAR (Differential Synthetic Aperture Radar Interferometry), have allowed the integration and improvement of the observation capabilities of ground-based methods thanks to their effectiveness in collecting displacement measurements on many non-destructive control points, corresponding to radar reflecting targets. The availability of such a large number of points of measurement, which are distributed along the whole structure and are characterized by millimetric accuracy on displacement rates, can be profitably adopted for the calibration of numerical models. These models are implemented to simulate the structural behaviour of a dam under conditions of stress thus improving the ability to maintain safety standards. In this work, after having analysed how advanced DInSAR can effectively enhance the results from traditional monitoring systems that provide comparable accuracy measurements on a limited number of points, an FEM model of the Genzano di Lucania earth dam is developed and calibrated. This work is concentrated on the advanced DInSAR technique referred to as Small BAseline Subset (SBAS) approach, benefiting from its capability to generate deformation time series at full spatial resolution and from multi-sensor SAR data, to measure the vertical consolidation displacement of the Genzano di Lucania earth dam

Analysis of regional large-gradient land subsidence in the Alto Guadalentín Basin (Spain) using open-access aerial LiDAR datasets

Land subsidence associated with groundwater overexploitation in the Alto Guadalentín Basin (Spain) aquifer system has been detected during the last decades. In this work, for the first time, we propose a new point cloud differencing methodology to detect land subsidence at basin scale, based on the multiscale model-to-model cloud comparison (M3C2) algorithm. This method is applied to two open-access airborne LiDAR datasets acquired in 2009 and 2016, respectively. First the internal edge connection errors in the different flight lines were addressed by means of a smoothing point cloud method. LiDAR datasets capture information from ground and non-ground points. Therefore, a method combining gradient filtering and cloth simulation filtering (CSF) algorithms was applied to remove non-ground points. The iterative closest point (ICP) algorithm was used for point cloud registration of both point clouds exhibiting a very stable and robust performance. The results show that vertical deformation rates are up to −14 cm/year in the basin from 2009 to 2016, in agreement with the displacement reported by previous studies. LiDAR results have been compared to the velocity measured by continuous GNSS stations and an InSAR dataset. For the GNSS-LiDAR and InSAR-LiDAR comparison, we computed a common 100 × 100 m grid in order to assess any similarities and discrepancies. The results show a good agreement between the vertical displacements obtained from the three different surveying techniques. Furthermore, LiDAR results were compared with the distribution of compressible soil thickness showing a clear relationship. The study underlines the potential of open-access and non-customized LiDAR to monitor the distribution and magnitude of vertical deformations in areas prone to be affected by groundwater-withdrawal-induced land subsidence.This research was funded by the ESA-MOST China DRAGON-5 project (ref. 59339) and by a Chinese Scholarship Council studentship awarded to Liuru Hu (Ref. 202004180062). María I. Navarro-Hernández and Guadalupe Bru are funded by the PRIMA programme supported by the European Union under grant agreement No 1924, project RESERVOIR

A GeoNode-based platform for an effective exploitation of advanced DInSAR measurements

This work presents the development of an efficient tool for managing, visualizing, analysing, and integrating with other data sources, the deformation time-series obtained by applying the advanced differential interferometric synthetic aperture radar (DInSAR) techniques. To implement such a tool we extend the functionalities of GeoNode, which is a web-based platform providing an open source framework based on the Open Geospatial Consortium (OGC) standards, that allows development of Geospatial Information Systems (GIS) and Spatial Data Infrastructures (SDI). In particular, our efforts have been dedicated to enable the GeoNode platform to effectively analyze and visualize the spatio/temporal characteristics of the DInSAR deformation time-series and their related products. Moreover, the implemented multi-thread based new functionalities allow us to efficiently upload and update large data volumes of the available DInSAR results into a dedicated geodatabase. The examples we present, based on Sentinel-1 DInSAR results relevant to Italy, demonstrate the effectiveness of the extended version of the GeoNode platform

Using Ray Tracing to Improve Bridge Monitoring With High-Resolution SAR Satellite Imagery

While satellite Persistent Scatterer SAR Interferometry (PSI) is an effective technique to monitor the health of structures via selection of long-term coherent pixels, detailed interpretation of displacement measurements requires knowledge of which surfaces, the reflection is coming from. Ray tracing algorithms can be used to simulate SAR backscatter for structures, and link observed PS pixels to specific parts of structures. We investigate the reflectivity of three bridges in London for a high-resolution TerraSAR-X dataset, using a ray tracing technique. Artificial reflectors are mounted on one of the bridges. We compare the simulated backscatter with the location of points selected as PS pixels using a stack of 38 TerraSAR-X images. The results confirm that we can predict overall scattering behaviour of a bridge using SAR simulation techniques when we have access to a 3D model of the structure. However, the results of simulation depend on the level of details in the 3D model and a high-detailed 3D model including corner reflectors allows the ray tracing technique to perfectly simulate position of the strong scatterers. This approach can help designers increase the SAR reflectivity of a bridge in the design phase of structural bridge assets, or in a retrofit phase, by installing artificial reflectors. We also link the strong scatterers in the reflectivity map to the corresponding scattering surfaces in the structural model that contributed to the signal. This allows the end-users of the InSAR products to better understand which sections of a bridge are moving when a PS pixel indicates displacement

Analysis of satellite data applicability for rock glacier creep monitoring

Analýza využitelnosti družicových dat pro monitoring pohybu skalních ledovců Abstrakt Skalní ledovce jsou typickým povrchovým tvarem periglaciálního prostředí velehor. Pohyb aktivních skalních ledovců a změny v jeho rychlosti jsou důležitým indikátorem změn klimatu. V případě nestability mohou skalní ledovce představovat ohrožení pro antropogenní objekty a/nebo obydlené oblasti. Předkládaná práce se zabývá otázkou monitoringu pohybu skalních ledovců s využitím družicových dat. Představuje a popisuje dvě základní metody pro detekci a měření pohybu povrchových tvarů reliéfu na optických a radarových snímcích. Těmito metodami jsou ztotožnění obrazu a diferenční radarová interferometrie. Cílem práce je hodnocení využitelnosti daných metod ve výzkumu pohybu skalních ledovců. Práce poskytuje přehled existujících družicových dat a také rozbor jejich vhodnosti pro analýzu v závislosti na rychlosti pohybu skalních ledovců. Klíčová slova: dálkový průzkum, monitoring pohybu, skalní ledovce, ztotožnění obrazu, DInSARAnalysis of satellite data applicability for rock glacier creep monitoring Abstract Rock glaciers are characteristic forms of periglacial high mountain environments. The creeping of active rock glaciers and changes in its velocity are important indicators of climate change. If unstable, rock glaciers can impose hazards to anthropogenic objects and/or populated areas. The presented thesis deals with the question of rock glacier creep monitoring with the use of satellite data. Two main methods for detecting and measuring the movement of landforms on optical and radar imagery are introduced. These methods are image matching and differential SAR interferometry. The goal of the thesis is to evaluate the applicability of the given methods for the research of the movement of rock glaciers. The thesis provides an overview of existing satellite data as well as an analysis of their suitability for research depending on rock glacier velocity. Keywords: remote sensing, movement monitoring, rock glaciers, image matching, DInSARDepartment of Applied Geoinformatics and CartographyKatedra aplikované geoinformatiky a kartografiePřírodovědecká fakultaFaculty of Scienc

Measuring Coseismic Deformation With Spaceborne Synthetic Aperture Radar: A Review

In the past 25 years, space-borne Synthetic Aperture Radar imagery has become an increasingly available data source for the study of crustal deformation associated with moderate to large earthquakes (M > 4.0). Coseismic surface deformation can be measured with several well-established techniques, the applicability of which depends on the ground displacement pattern, on several radar parameters, and on the surface properties at the time of the radar acquisitions. The state-of-the-art concerning the measurement techniques is reviewed, and their application to over 100 case-studies since the launch of the Sentinel-1a satellite is discussed, including the performance of the different methods and the data processing aspects, which still constitute topics of ongoing research

How second generation SAR systems are impacting the analysis of ground deformation

Abstract In recent years, a second generation of Synthetic Aperture Radar (SAR) satellite sensor has been designed and, partially, put into operation, leading to an important breakthrough in Earth Science studies. The common characteristics of such new systems are, indeed, a reduced revisit time (as short as a few days) and, in most cases, an improved spatial resolution (as small as a few meters), providing scientists with unprecedented data for the mapping and monitoring of natural and human-induced hazards. This paper provides an overview on the new observational capability offered by the second generation of SAR sensors, especially in the field of ground deformation analysis for mitigating the risk associated with natural and human-induced hazards. In particular, we exploit the high resolution X-band data acquired by the COSMO-SkyMed (CSK) constellation to show how deformation phenomena characterized by limited spatial extent and extremely fast dynamics can be detected and investigated in details. Whenever possible, we compare the achieved results with those obtained by using data collected by the first generation ERS-1/2 and ENVISAT systems. A comparison with one ALOS satellite dataset is also included. Most of the results, based on the application of Differential SAR Interferometry (DInSAR) techniques, highlight how this technology is not anymore just a sophisticated tool for remotely studying surface deformation phenomena, but it is becoming an operational system for near-real time deformation monitoring. Moreover, we also show how the improved spatial resolution extends the possibility to exploit SAR image amplitude, instead of phase, for direct comparison with optical data and for imaging large deformation episodes, typically associated with strong seismic events, for which DInSAR may fail

Estimation and validation of InSAR-derived surface displacements at temperate raised peatlands

Peatland surface motion derived from satellite-based Interferometry of Synthetic Aperture Radar (InSAR) is potentially a proxy for groundwater level variations and greenhouse gas emissions from peat soils. Ground validation of these motions at equivalent temporal resolution has proven problematic, either because of limitations of traditional surveying methods or because of limitations with past InSAR time-series approaches. Novel camera-based instrumentation has enabled in-situ measurement of peat surface from mid-2019 to mid-2022 at two large temperate raised bogs undergoing restoration – Cors Fochno and Cors Caron, in mid-Wales, United Kingdom. The cameras provided continuous measurements at sub-millimetre precision and sub-daily temporal resolution. From these data and Sentinel-1 acquisitions spanning mid-2015 to early-2023, we demonstrate that accurate peat surface motion can be derived by InSAR when a combination of interferometric networks with long and short temporal baselines is used. The InSAR time series data closely match the in-situ data at both bogs, and in particular recover well the annual peat surface oscillations of 10-40 mm. Pearson's values for the point-wise correlation of in-situ and InSAR displacements are 0.8–0.9, while 76% of differences are < ±5 mm and 93% are < ±10 mm. RMSE values between multi-annual in-situ and InSAR peat surface displacement rates are ~7 mm·yr−1 and decrease to ∼3.5 mm for individual peat surface motion measurements. Larger differences mainly occur during drought periods. Multi-annual displacement velocities rates based on InSAR indicate long-term subsidence at Cors Caron (maximum −7 mm·yr−1), while Cors Fochno exhibits subsidence at the centre and uplift at the margins (−9 mm·yr−1 to +5 mm·yr−1). Because of the annual peat surface oscillations, however, more robust ground validation of the long-term peat surface motion rates derived from InSAR requires longer time-series of in-situ measurements than are presently available. Nonetheless, the InSAR-derived surface motion rates correlate well spatially with both peat dome elevation and peat thickness. In addition, the annual oscillations in surface motion are synchronous with or lag slightly behind groundwater level changes. A coarse ratio of 10:1 is observed between annual changes in groundwater level and peat surface displacement. Satellite-based InSAR derived from a fusion of short- and long-term temporal baseline networks can thus enable accurate monitoring of hydrologically driven surface motions of moderately degraded to intact temperate raised peatlands