Discontinuous GBSAR deformation monitoring

This paper is focused on deformation monitoring using the Ground-Based SAR (GBSAR) technique and a particular data acquisition configuration, which is called discontinuous GBSAR (D-GBSAR). In the most commonly used GBSAR configuration, the radar is left installed in situ, acquiring data periodically, e.g. every few minutes. Deformations are estimated by processing sets of GBSAR images acquired during several weeks or months, without moving the system. By contrast, in the D-GBSAR the radar is installed and dismounted at each measurement campaign, revisiting a given site periodically. This configuration is useful to monitor slow deformation phenomena. This paper outlines the D-GBSAR data analysis procedure implemented by the authors. This is followed by a discussion of some specific aspects of D-GBSAR monitoring. Two successful examples of D-GBSAR monitoring are discussed: one concerns an urban area, while the second one involves a rural area where the monitoring requires the use of artificial corner reflectors

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

Geodetic monitoring of complex shaped infrastructures using Ground-Based InSAR

In the context of climate change, alternatives to fossil energies need to be used as much as possible to produce electricity. Hydroelectric power generation through the utilisation of dams stands out as an exemplar of highly effective methodologies in this endeavour. Various monitoring sensors can be installed with different characteristics w.r.t. spatial resolution, temporal resolution and accuracy to assess their safe usage. Among the array of techniques available, it is noteworthy that ground-based synthetic aperture radar (GB-SAR) has not yet been widely adopted for this purpose. Despite its remarkable equilibrium between the aforementioned attributes, its sensitivity to atmospheric disruptions, specific acquisition geometry, and the requisite for phase unwrapping collectively contribute to constraining its usage. Several processing strategies are developed in this thesis to capitalise on all the opportunities of GB-SAR systems, such as continuous, flexible and autonomous observation combined with high resolutions and accuracy. The first challenge that needs to be solved is to accurately localise and estimate the azimuth of the GB-SAR to improve the geocoding of the image in the subsequent step. A ray tracing algorithm and tomographic techniques are used to recover these external parameters of the sensors. The introduction of corner reflectors for validation purposes confirms a significant error reduction. However, for the subsequent geocoding, challenges persist in scenarios involving vertical structures due to foreshortening and layover, which notably compromise the geocoding quality of the observed points. These issues arise when multiple points at varying elevations are encapsulated within a singular resolution cell, posing difficulties in pinpointing the precise location of the scattering point responsible for signal return. To surmount these hurdles, a Bayesian approach grounded in intensity models is formulated, offering a tool to enhance the accuracy of the geocoding process. The validation is assessed on a dam in the black forest in Germany, characterised by a very specific structure. The second part of this thesis is focused on the feasibility of using GB-SAR systems for long-term geodetic monitoring of large structures. A first assessment is made by testing large temporal baselines between acquisitions for epoch-wise monitoring. Due to large displacements, the phase unwrapping can not recover all the information. An improvement is made by adapting the geometry of the signal processing with the principal component analysis. The main case study consists of several campaigns from different stations at Enguri Dam in Georgia. The consistency of the estimated displacement map is assessed by comparing it to a numerical model calibrated on the plumblines data. It exhibits a strong agreement between the two results and comforts the usage of GB-SAR for epoch-wise monitoring, as it can measure several thousand points on the dam. It also exhibits the possibility of detecting local anomalies in the numerical model. Finally, the instrument has been installed for continuous monitoring for over two years at Enguri Dam. An adequate flowchart is developed to eliminate the drift happening with classical interferometric algorithms to achieve the accuracy required for geodetic monitoring. The analysis of the obtained time series confirms a very plausible result with classical parametric models of dam deformations. Moreover, the results of this processing strategy are also confronted with the numerical model and demonstrate a high consistency. The final comforting result is the comparison of the GB-SAR time series with the output from four GNSS stations installed on the dam crest. The developed algorithms and methods increase the capabilities of the GB-SAR for dam monitoring in different configurations. It can be a valuable and precious supplement to other classical sensors for long-term geodetic observation purposes as well as short-term monitoring in cases of particular dam operations

Advanced Ground-Based Real and Synthetic Aperture Radar

Ground-based/terrestrial radar interferometry (GBRI) is a scientific topic of increasing interest in recent years. The GBRI is used in several field as remote sensing technique for monitoring natural environment (landslides, glacier, and mines) or infrastructures (bridges, towers). These sensors provide the displacement of targets by measuring the phase difference between sending and receiving radar signal. If the acquisition rate is enough the GBRI can provide the natural frequency, e.g. by calculating the Fourier transform of displacement. The research activity, presented in this work, concerns design and development of some advanced GBRI systems. These systems are related to the following issue: detection of displacement vector, Multiple Input Multiple Output (MIMO) and radars with 3D capability

Novel Approaches in Landslide Monitoring and Data Analysis

Significant progress has been made in the last few years that has expanded the knowledge of landslide processes. It is, therefore, necessary to summarize, share and disseminate the latest knowledge and expertise. This Special Issue brings together novel research focused on landslide monitoring, modelling and data analysis

Development of LiDAR assisted terrestrial radar interferometry for rock deformation monitoring

Rock and soil slope movements cost millions of dollars annually. During the past few decades, engineers have relied on traditional methods to detect slope movements. These tools are valuable for small spatial areas but, may not be adequate or cost effective for large spatial areas. Remote sensing methods such as terrestrial laser scanning (TLS) and terrestrial radar interferometry (TRI) provide excellent spatial coverage, and with adequate post-data-processing software, sub-millimetric scale deformation sensitivity can be achieved. This work will present a comparative experimental study between TLS and TRI. The comparative experimental study will allow us to achieve the two main objectives of this research: 1. The development of a methodology to correct repositioning errors of the TRI during discontinuous measurement campaigns. 2. The development of a methodology to use TLS as an independent measurement device to constrain the results of the TRI when rock displacements exceed multiple wavelengths of the instrument or displacements exceed one quarter of the wavelength of the instrument. Results from the measurement campaigns show that sub-millimetric displacements can be detected with both TLS and TRI systems. Furthermore, TLS systems are widely available, cheaper, lighter, and easier to operate than TRI systems. Data can also be reduced faster, and the results more easily interpreted than with TRI systems. These advantages make TLS systems ideal for rock slope evaluation for highway projects, especially when time, cost, and public opinion are major concerns for the state\u27s Department of Transportation --Abstract, page iv

MONITORAGGIO DI DISSESTI FRANOSI CON METODOLOGIA INTEGRATA BASATA SULL'USO DI SISTEMA RADAR INTERFEROMETRICO TERRESTRE (GBSAR)

2013/2014L’analisi critica del monitoraggio di frane con l’utilizzo dell’interferometria radar da terra è stata lo scopo di questa tesi di dottorato di ricerca in geoscienze. Il progetto prende lo spunto dalla possibilità di poter coniugare le esigenze di una struttura preposta al monitoraggio di dissesti franosi, la disponibilità di tecnologie innovative non invasive e la loro fattibilità nel contesto regionale. L’idea di poter utilizzare ed analizzare criticamente i risultati di una serie di monitoraggi è stata quindi presa come linea guida per questo ciclo di dottorato di ricerca in geoscienze. Nell’ambito delle opere di prevenzione da calamità naturali, il Servizio geologico della Regione Autonoma Friuli Venezia Giulia, di cui l’autore è un componente, ha ritenuto di attivare il monitoraggio di tre frane ubicate nel territorio di competenza con l’utilizzo di misure di superficie eseguite con tecnologie basate sull’uso del sistema radar interferometrico con lo scopo di identificare delle zone caratterizzate da movimenti di versante, così da: • integrare le conoscenze pregresse sulla determinazione della forma ed estensione della massa in movimento nonché della distribuzione di pressioni e sforzi; • determinare gli spostamenti differenziali dell’area di frana; • stimare il campo di velocità e la sua interrelazione con fattori esterni quali piogge o temperatura; I siti individuati per questo piano di monitoraggio sono caratterizzati da diverse tipologie di dissesto e di condizioni al contorno. La loro designazione è stata fatta seguendo questo criterio guida. Considerando l’eterogeneità del territorio regionale sono stati scelti: • Ligosullo (UD): il sito in oggetto è rappresentato dal centro urbano di Ligosullo, caratterizzato da un fenomeno di instabilità generalizzato con tassi di deformazione dell’ordine di alcuni cm/anno; • Cimolais (PN): Il sito in oggetto è rappresentato una parete rocciosa, caratterizzata da fenomeni localizzati di crollo; • Erto e Casso, località La Pineda (PN): il sito in oggetto è rappresentato da una parte dell’accumulo di una paleo frana del monte Salta. Caratterizzato da una zona calanchiva in evoluzione, caratterizzata da frane superficiali diffuse. I motivi che hanno individuato il radar interferometrico terrestre come principale metodo di monitoraggio sono legati alle principali caratteristiche della tecnica, ovvero: • sistema remoto che consente di misurare spostamenti del fronte instabile senza la necessità teorica di installare riflettori artificiali e quindi di accedere direttamente alla zona instabile; • capacità di fornire mappe di spostamento dell’intero versante; • misure in near real time: è possibile elaborare i dati acquisiti in maniera automatica e fornire i risultati in tempo quasi reali (con pochi minuti di ritardo rispetto all’acquisizione); • misure in qualsiasi condizione meteorologica, sia di giorno che di notte grazie all’uso di un sistema radar; • misure ad elevata accuratezza (tra il decimo di millimetro ed il millimetro in funzione della distanza) nate dall’applicazione della ricerca spaziale, che consente di determinare l’entità dello spostamento di un oggetto confrontando le informazioni di fase delle onde elettromagnetiche riflesse dall’oggetto in diversi istanti di tempo.XXVI Ciclo197

Insights into Rockfall from Constant 4D Monitoring

Current understanding of the nature of rockfall and their controls stems from the capabilities of slope monitoring. These capabilities are fundamentally limited by the frequency and resolution of data that can be captured. Various assumptions have therefore arisen, including that the mechanisms that underlie rockfall are instantaneous. Clustering of rockfall across rock faces and sequencing through time have been observed, sometimes with an increase in pre-failure deformation and pre-failure rockfall activity prior to catastrophic failure. An inherent uncertainty, however, lies in whether the behaviour of rockfall monitored over much shorter time intervals (Tint) is consistent with that previously monitored at monthly intervals, including observed failure mechanisms, their response to external drivers, and pre-failure deformation. To address the limitations of previous studies on this topic, 8 987 terrestrial laser scans have been acquired over 10 months from continuous near-real time monitoring of an actively failing coastal rock slope (Tint = 0.5 h). A workflow has been devised that automatically resolves depth changes at the surface to 0.03 m. This workflow filters points with high positional uncertainty and detects change in 3D, with both approaches tailored to natural rock faces, which commonly feature sharp edges and partially occluded areas. Analysis of the resulting rockfall inventory, which includes > 180 000 detachments, shows that the proportion of rockfall < 0.1 m3 increases with more frequent surveys for Tint < ca. 100 h, but this trend does not continue for surface comparison over longer time intervals. Therefore, and advantageously, less frequent surveys will derive the same rockfall magnitude-frequency distribution if captured at ca. 100 h intervals as compared to one month or even longer intervals. The shape and size of detachments shows that they are more shallow and smaller than observable rock mass structure, but appear to be limited in size and extent by jointing. Previously explored relationships between rockfall timing and environmental and marine conditions do not appear to apply to this inventory, however, significant relationships between rockfall and rainfall, temperature gradient and tides are demonstrated over short timescales. Pre-failure deformation and rockfall activity is observed in the footprint of incipient rockfall. Rockfall activity occurs predominantly within the same ca. 100 h timescale observed in the size-distribution analysis, and accelerated deformation is common for the largest rockfall during the final 2 h before block detachment. This study provides insights into the nature and development of rockfall during the period prior to detachment, and the controls upon it. This holds considerable implications for our understanding of rockfall and the improvement of future rockfall monitoring