Surface Displacement Monitoring Research Articles

Effect of digital elevation models on monitoring slope displacements in open-pit mine by differential interferometry synthetic aperture radar

Abstract Displacement monitoring in open-pit mines is one of the important tasks for safe management of mining processes. Differential interferometric synthetic aperture radar (DInSAR), mounted on an artificial satellite, has the potential to be a cost-effective method for monitoring surface displacements over extensive areas, such as open-pit mines. DInSAR requires the ground surface elevation data in the process of its analysis as a digital elevation model (DEM). However, since the topography of the ground surface in open-pit mines changes largely due to excavations, measurement errors can occur due to insufficient information on the elevation of mining areas. In this paper, effect of different elevation models on the accuracy of the displacement monitoring results by DInSAR is investigated at a limestone quarry. In addition, validity of the DInSAR results using an appropriate DEM is examined by comparing them with the results obtained by global positioning system (GPS) monitoring conducted for three years at the same limestone quarry. It is found that the uncertainty of DEMs induces large errors in the displacement monitoring results if the baseline length of the satellites between the master and the slave data is longer than a few hundred meters. Comparing the monitoring results of DInSAR and GPS, the root mean square error (RMSE) of the discrepancy between the two sets of results is less than 10 mm if an appropriate DEM, considering the excavation processes, is used. It is proven that DInSAR can be applied for monitoring the displacements of mine slopes with centimeter-level accuracy.

Accuracy Improvement of Binocular Vision Measurement System for Slope Deformation Monitoring.

This paper studies the limitations of binocular vision technology in monitoring accuracy. The factors affecting the surface displacement monitoring of the slope are analyzed mainly from system structure parameters and environment parameters. Based on the error analysis theory, the functional relationship between the structure parameters and the monitoring error is studied. The error distribution curve is obtained through laboratory testing and sensitivity analysis, and parameter selection criteria are proposed. Corresponding image optimization methods are designed according to the error distribution curve of the environment parameters, and a large number of tests proved that the methods effectively improved the measurement accuracy of slope deformation monitoring. Finally, the reliability and accuracy of the proposed system and method are verified by displacement measurement of a slope on site.

Prediction of Mining Subsidence in Shallow Coal Seam

Theoretical calculation, numerical simulation, and field measurement were combined to study the recovery of coal resources in the 5th pan area of Dianping Coal Mine without damaging surface buildings. A mathematical model was established to predict the settlement range and displacement of the surface after coal mining. The FLAC3D5.0 program was used to simulate the evolution law of the overburden strata under the coal mining conditions of the study area. The lateral influence range was 45.8 m and 42.4 m, and the maximum surface subsidence was 2.604 m and 2.78 m, respectively. The mining boundary of the 5-210 working face was designed using the result of the simulation program. Real-time dynamic observation data collected from 18 surface displacement monitoring points measured surface subsidence as 2.69 m. The civil construction protection area was not deformed. The working face provided safe recovery of 1,471,446,000 kg of coal, resulting in significant economic and social benefits.

Rainfall-induced reactivation mechanism of a landslide with multiple-soft layers

A study on the site investigation data from the Chengnan landslide, which was a partially reactivated ancient landslide in Meigu County, Xichang City, China, is presented. To explore the reactivation mechanism of the Chengnan landslide, we conducted site investigation, surface displacement monitoring, deep displacement monitoring, finite element analysis, and limit the equilibrium analysis of the Chengnan landslide. The results indicated that the Chengnan landslide experienced multiple reactivations. It was initially reactivated in 2002 along the first clay layer at a depth of 14 m; after comprehensive treatment measures, which included excavating to reduce loads, improving the drainage system, and installing anti-sliding piles in 2006, further deformation was prevented. However, heavy rainfall in 2007 caused groundwater infiltration, softening the second clay layer at a depth of 28 m and transforming it into a new sliding surface (i.e., the second sliding surface). Consequently, Chengnan landslide was reactivated again along the second sliding surface, and the anti-sliding piles moved together with upper sliding body along the second sliding surface because this sliding surface was located deeper than the anti-sliding piles. Based on the results of this study, a multilayer creeping–tension mechanism controlled by multiple soft layers of the Chengnan landslide was proposed. This interesting case study should be considered from a scientific and technical point of view; some valuable suggestions for site investigation and treatment of this kind of landslide are also proposed.

Slope structures and formation of rock-soil aggregate landslides in deeply incised valleys

Rock-soil aggregate landslides (RSALs) are a common geological hazard in deeply incised valleys in southwestern China. Large-scale RSALs are widely distributed in the upper reaches of the Dadu River, Danba County, Sichuan Province, and are influenced by slope structure, which can be divided into open, lock, strip, and dumbbell types, as well as soil type and meso-structure, which can be classified as layered rock-soil aggregate, block-soil, and grain-soil. In this study, the evolution of four types of structures, such as layered-dumbbell, block-soil lock, banded block-soil, and block-soil open types, were analyzed by field surveys, surface and deep displacement monitoring, and Flac3D. It was found that the Danba reach of the Dadu River showed incised valley through the evolution from wide to slow valley affected by internal and external geological processes since the Quaternary Glaciation. In the layered-dumbbell rock-soil aggregate, the main sliding pattern is multi-stage sliding at different depths. Circular sliding in the trailing edge and plane sliding along the bedrock in the front edge body occur in the block-soil-lock type aggregate. Large-scale multi-level and circular sliding over long distances occur in the banded block-soil aggregate. The block-soil open type is stable, with only circular sliding occurring in local and shallow surfaces of the body. The monitoring and numerical simulation results further show that slope structure and regularity have diversified with RSALs. The results provide a basis for analyzing the stability mechanism of RSALs and preventing RSALs in deeply incised valleys.

Redundancy and coherence of multi-method displacement monitoring data as key issues for the analysis of extremely slow landslides (Isarco valley, Eastern Alps, Italy)

The paper describes the study of two extremely slow, active-continuous, deep-seated landslides located in the Isarco Valley (Eastern Alps, Italy): a Multiple Rotational Rock Slide (MRRS) and partial reactivation of a Deep-Seated Gravitational Slope Deformation (DSGSD). Both landslides interact with viaducts on the E45 highway. Extensive multi-method field investigation, monitoring of surface and subsurface displacements and limit equilibrium stability analyses were adopted to fully characterize slope dynamics. In order to overcome the limitations due to the systematic errors affecting each single monitoring system and analysis method, an operative framework based on redundancy and coherence tests was introduced to check the reliability of the data and results. In this framework, the geological and geotechnical models of the investigated slopes were progressively refined. This allowed assessment of the type of interaction between the slopes and the highway viaducts.

Feasibility study of surface motion tracking with millimeter wave technology during radiotherapy.

Continuous monitoring of patient movement is crucial to administering safe radiation therapy (RT). Conventional optical approaches often cannot be used when the patient's surface is blocked by immobilization devices. Millimeter waves (mmWaves) are capable of penetrating nonconductive objects. In this study, we investigated using mmWave technology to monitor patient surface displacements, as well as breathing and cardiac phases, through clothing and body fixtures. A mmWave device was mounted inside the bore of a ring-based radiotherapy linear accelerator and pointed at a reflective surface on top of the couch. Measurements were obtained at displacements of 10, 7.5, 5.0, 2.5, and 1.0mm at heights 100, 150, and 200 mm below isocenter. Submillimeter displacements were performed at a height of 200mm. Additionally, millimeter and submillimeter displacements were measured with and without a gown and body mold placed between the surface and the sensor. The device was programmed to transmit chirp signals at 77-81GHz. The subject's surface was detected by fast Fourier transform (FFT) of the reflected chirp signal within a rough range bin. Fine displacements within that range bin were calculated through phase extraction and phase demodulation. The displacement data were sent through two separate bandpass filters with passbands of 0.1-0.6 and 0.8-2.0Hz to obtain the subject's breathing and cardiac waveforms, respectively. The breathing and cardiac measurements were compared to those of a Vernier Respiration Monitor Belt and an electrocardiogram (EKG), respectively, to assess validity. The device was able to detect millimeter and submillimeter displacements as small as 0.1mm, as well as monitor displacement with an accuracy within 1mm in the presence of an obstructive object. The device's breathing and cardiac waveforms exhibited a strong phase correlation between the respiration monitor belt (ρ=0.9156) and EKG (ρ=0.7895), respectively. The mmWave device can monitor surface displacements with an accuracy better than 0.1mm without obstructions and better than 1mm with obstructions. It can also provide real-time monitoring of breathing and cardiac waveforms simultaneously with high correlation with traditional respiratory and cardiac monitoring devices. Overall, mmWave technology demonstrates potential for motion monitoring in the field of radiation oncology.

Acoustic Emission Characteristics of Normal and Layered Concrete Blocks during Dilating/Static Fracture

Static fracturing technology is one of the most effective methods for localized breaking of rock and concrete. Layered concrete and rock structures are commonly seen in engineering applications such as breaking of concrete buildings, stone cutting, and excavation of rock in underground spaces. Therefore, it is essential to study the static fracturing characteristics of layered concrete to ensure the safety of engineering construction processes. In this paper, using acoustic emission (AE) technology and surface displacement monitoring, the deformation and fracturing of ordinary‐strength concrete, concrete with a soft interlayer, and layered concrete (with strength decreasing successively by layer) were studied under the effect of a static (or soundless) cracking agent (SCA). The experimental results indicated that (1) AE activity of the two layered concrete test blocks during static fracturing showed a gradually increasing trend, while that of the ordinary‐strength concrete tended to first increase and then decrease; (2) for the concrete test block with a soft interlayer sandwiched by high‐strength layers, the AE events reached a maximum in the transfer of expansion pressure stage, which accounted for 47.11% of the total value in static cracking; the macroscopic damage to layered concrete test blocks comprising multiple interlaid layers with different strengths mainly occurred in the fracturing stage, during which the AE events and AE energy accounted for 76.22% and 66.94%, respectively, of those in the whole static fracturing process; and (3) the duration of static fracturing prolonged with the increase of the overall strength of the concrete test blocks. The results provide a useful experimental reference for the application of static fracturing technology in the breaking of layered concrete and rock.

A Ground Surface Deformation Monitoring InSAR Method Using Improved Distributed Scatterers Phase Estimation

Persistent scatterer interferometric synthetic aperture radar (PSInSAR) technology provides a powerful tool for detecting ground surface displacements. However, one of its major limitations is an insufficient number of coherence points due to decorrelation. In this article, we propose an effective ground surface displacement monitoring approach based on the Stanford method for persistent scatterer (StaMPS). This approach dramatically increases the density of coherence points by jointly exploiting persistent scatterer (PS) and distributed scatterer (DS) points. In particular, we develop a new DS phase estimation method based on nonlinear optimization estimation (NLE) and exploit it in our approach. The NLE can obtain better DS phase noise reduction, can detect more coherence points, and requires slightly less computational time than conventional maximum-likelihood estimation (MLE). To demonstrate the effectiveness of our new approach, we apply it over 24 Envisat SAR images acquired over Tucson, Arizona in the USA. The coherence pixel density is increased substantially (> 6 times) compared with the conventional StaMPS-based PSInSAR approach. As for the improvement of our NLE over MLE, it can detect 11.7% more coherence pixels, can achieve better phase noise reduction, and needs approximately one third less computational time. These results validate the effectiveness of our new approach and suggest its great potential for land displacement measurements.

Improvement of Persistent Scatterer Interferometry to Detect Large Non-Linear Displacements with the 2π Ambiguity by a Non-Parametric Approach

Persistent scatterer interferometry (PSI) is commonly applied to monitor surface displacements with millimetric precision. However, this technique still has trouble estimating non-linear displacements because the algorithm is designed for the slow and linear displacements. Additionally, there is a variety of non-linear displacement types, and finding an appropriate displacement model for PSI is still assumed to be a fairly large task. In this paper, the conventional PSI technique is extended using a non-parametric non-linear approach (NN-PSI), and the performance of the extended method is investigated by simulations and actual observation data processing with TerraSAR-X. In the simulation, non-linear displacements are modeled by the magnitudes and periods of the displacement, and the evaluation of NN-PSI is conducted. According to the simulation results, the maximum magnitude of the displacement that can be estimated by NN-PSI is two and a half times the magnitude of the SAR sensor’s wavelength (2.5λ that is roughly equivalent to 8 cm for X-band, 14 cm for C-band, and 60 cm for L-band), and the period of the displacement is about three months. However, this displacement cannot be reconstructed by the conventional PSI due to the limitation, known as the 2π displacement ambiguity. The result of the observation data processing shows that a large displacement with the 2π ambiguity can be estimated by NN-PSI as the simulation results show, but the conventional PSI cannot reconstruct it. In addition, a different approach, Small BAseline Subset (SBAS), is applied to the same data to ensure the accuracy of results, and the correlation between NN-PSI and SBAS is 0.95, while that between the conventional PSI and SBAS is –0.66. It is concluded that NN-PSI enables the reconstruction of non-linear displacements by the non-parametric approach and the expansion of applications to measure surface displacements that could not be measured due to the limitations of the traditional PSI methods.

Landslide Deformation Monitoring by Adaptive Distributed Scatterer Interferometric Synthetic Aperture Radar

Landslide is the second most frequent geological disaster after earthquake, which causes a large number of casualties and economic losses every year. China frequently experiences devastating landslides in mountainous areas. Interferometric Synthetic Aperture Radar (InSAR) technology has great potential for detecting potentially unstable landslides across wide areas and can monitor surface displacement of a single landslide. However traditional time series InSAR technology such as persistent scatterer interferometry (PSI) and small-baseline subset (SBAS) cannot identify enough points in mountainous areas because of dense vegetation and steep terrain. In order to improve the accuracy of landslide hazard detection and the reliability of landslide deformation monitoring in areas lacking high coherence stability point targets, this study proposes an adaptive distributed scatterer interferometric synthetic aperture radar (ADS-InSAR) method based on the spatiotemporal coherence of the distributed scatterer (DS), which automatically adjusts its detection threshold to improve the spatial distribution density and reliability of DS detection in the landslide area. After time series network modeling and deformation calculation of the ADS target, the displacement deformation of the landslide area can be accurately extracted. Shuibuya Town in Enshi Prefecture, Hubei Province, China, was used as a case study, along with 18 Sentinal-1A images acquired from March 2016 to April 2017. The ADS-InSAR method was used to obtain regional deformation data. The deformation time series was combined with hydrometeorological and related data to analyze landslide deformation. The results show that the ADS-InSAR method can effectively improve the density of DS distribution, successfully detect existing ancient landslide groups and determine multiple potential landslide areas, enabling early warning for landslide hazards. This study verifies the reliability and accuracy of ADS-InSAR for landslide disaster prevention and mitigation.

Monitoring and Analyzing Mountain Glacier Surface Movement Using SAR Data and a Terrestrial Laser Scanner: A Case Study of the Himalayas North Slope Glacier Area

The offset tracking technique based on synthetic aperture radar (SAR) image intensity information can estimate glacier displacement even when glacier velocities are high and the time interval between images is long, allowing for the broad use of this technique in glacier velocity monitoring. Terrestrial laser scanners, a non-contact measuring system, can measure the velocity of a glacier even if there are no control points arranged on a glacier. In this study, six COSMO-SkyMed images acquired between 31 July and 22 December 2016 were used to obtain the glacial movements of five glaciers on the northern slope of the central Himalayas using the offset tracking approach. During the period of image acquirement, a terrestrial laser scanner was used, and point clouds of two periods in a small area at the terminus of the Pingcuoliesa Glacier were obtained. By selecting three fixed areas of the point clouds that have similar shapes across two periods, the displacements of the centers of gravity of the selected areas were calculated by using contrast analyses of feature points. Although the overall low-density point clouds data indicate that the glacial surfaces have low albedos relative to the wavelength of the terrestrial laser scanner and the effect of its application is therefore influenced in this research, the registration accuracy of 0.0023 m/d in the non-glacial areas of the scanner’s measurements is acceptable, considering the magnitude of 0.072 m/d of the minimum glacial velocity measured by the scanner. The displacements from the point clouds broadly agree with the results of the offset tracking technique in the same area, which provides further evidence of the reliability of the measurements of the SAR data in addition to the analyses of the root mean squared error of the velocity residuals in non-glacial areas. The analysis of the movement of five glaciers in the study area revealed the dynamic behavior of these glacial surfaces across five periods. G089972E28213N Glacier, Pingcuoliesa Glacier and Shimo Glacier show increasing surface movement velocities from the terminus end to the upper part with elevations of 1500 m, 4500 m, and 6400 m, respectively. The maximum velocities on the glacial surface profiles were 31.69 cm/d, 62.40 cm/d, and 42.00 cm/d, respectively. In contrast, the maximum velocity of Shie Glacier, 50.60 cm/d, was observed at the glacier’s terminus. For each period, Glacier G090138E28210N exhibited similar velocity values across the surface profile, with a maximum velocity of 39.70 cm/d. The maximum velocities of G089972E28213N Glacier, Pingcuoliesa Glacier, and Shie Glacier occur in the areas where the topography is steepest. In general, glacial surface velocities are higher in the summer than in the winter in this region. With the assistance of a terrestrial laser scanner with optimized wavelengths or other proper ground-based remote sensing instruments, the offset tracking technique based on high-resolution satellite SAR data should provide more reliable and detailed information for local and even single glacial surface displacement monitoring.

Contribution of the BDS to availability and reliability improvement: A case study of dam surface displacement monitoring in China

The GPS-only system is limited in dam surface monitoring because of its low availability and reliability due to the visible satellites are not enough. This dilemma is expected to be solved through incorporating the China's BeiDou System (BDS). This contribution will quantitatively analyse the availability and reliability improvements from DBS in different shielding situations of dams. The analysis is conducted through simulating a dam obstruction with different size, azimuth and distance to receiver. The similar experiments are simulated in the area across China in order to explore these contributions in different locations. Quantitative analysis results derive conclusions: (1) In most areas, the availability improved from 50% of GPS-only to 95% of BDS + GPS when most of the GEO/IGSO satellites are not blocked, and to 70% even when most of GEO/IGSO satellites are blocked. (2) The average MDBs can be reduced by half when most of the GEO/IGSO satellites are not blocked, and by 10% even when most of GEO/IGSO satellites are blocked.

Comparison of leaf-off and leaf-on combined UAV imagery and airborne LiDAR for assessment of a post-mining site terrain and vegetation structure: Prospects for monitoring hazards and restoration success

Mining is an important human activity that significantly affects the landscape character, particularly through excavation of spoil material and its deposition on spoil banks. The information on terrain or vegetation cover of spoil banks is often required for two different reasons: (i) to monitor and prevent adverse effect of hazards associated with unstable terrain; and (ii) to assess restoration success. Traditionally used in situ methods for monitoring surface displacement or restoration success are restricted in terms of spatial and temporal coverage. Therefore, in this study, we assessed the value of photogrammetrically and Light Detection and Ranging (LiDAR) derived point clouds for characterizing a post-mining site. We acquired images under leaf-off and leaf-on conditions and showed that point densities of point clouds acquired photogrammetrically under leaf-off conditions exceeded densities of those acquired under leaf-on conditions and uniformly covered ground of the entire study area (an average density of 288 points per m2). In addition, the accuracy of the digital terrain model (DTM; 1 m resolution) derived from images acquired under leaf-off conditions was comparable to the LiDAR-derived DTM (RMSE of 0.19 m and 0.12 m, respectively). While LiDAR-derived DTM accuracies were consistent across vegetation categories (RMSE 0.12–0.14 m), accuracy of image-based DTMs declined in the following order: forest (RMSE 0.15 m), steppes (RMSE 0.21 m), and aquatic vegetation (RMSE 0.36 m). We suggest the leaf-off UAV imagery as a viable alternative for building DTMs that can be utilized for assessment of risks associated with instability of spoil banks terrain. In addition, we also suggest that a combination of acquisitions under leaf-off and leaf-on conditions have a potential to replace expensive airborne LiDAR surveys for applications requiring information on vegetation cover or vegetation height.

Application of InSAR in Surface Deformation Monitoring of Electric Power Line Selection

In the process of site selection and the facility construction in power engineering, the geological conditions of the foundation have an important impact on the displacement of completed power facilities. Usually, the conventional surface displacement has certain continuity in time and space. Therefore, in the initial stage of power line selection, the relatively stable geological conditions can greatly reduce the probability of major accidents due to ground deformation. As a new surface displacement monitoring method, InSAR can obtain the displacement monitoring results in long time series. This paper used 20 Sentinel-1A data to study the geological conditions of power line selection. Based on the fact that the vegetation coverage in the line selection area and the poor penetration of C-band data may cause serious body scattering correlation, we verified the possibility of obtaining accurate results in a long-time baseline with less influence on volume scattering decorrelation. Using this method, we obtained the surface history displacement line chart of the 220 kV power line to be erected in Laiyuan to Quanyu, Hebei Province. By analyzing 10 high coherence points on the line, we found that the largest historical surface displacement in the 18 months is less than 30mm, and the maximum cumulative deformation rate is only 12 mm/a, which meets the requirements of power line erection.

A New Nonlocal Method for Ground-Based Synthetic Aperture Radar Deformation Monitoring

Ground-based synthetic aperture radar (GBSAR) interferometry offers an effective solution for the monitoring of surface displacements with high precision. However, coherence estimation and phase filtering in GBSAR interferometry is often based on a rectangular window, resulting in estimation biases and resolution loss. To address these issues, conventional nonlocal methods developed for spaceborne synthetic aperture radar are investigated with GBSAR data for the first time. Based on investigation and analysis, an efficient similarity measure is proposed to identify pixels with similar amplitude behaviors and a comprehensive nonlocal method is presented on the basis of this concept with the aim of overcoming current limitations. Pixels with high similarity are identified from a large search window for each point based on a stack of GBSAR single look complex images. Coherence is calculated based on the selected sibling pixels and then enhanced by the second kind statistic estimator. Nonlocal means filtering is also performed based on the sibling pixels to reduce interferometric phase noise. Experiments were conducted using short- and long-term GBSAR interferograms. Qualitative and quantitative analyses of the proposed nonlocal method and other existing techniques demonstrate that the new approach has advantages in terms of coherence estimation and phase filtering capability. The proposed method was integrated into a complete GBSAR small baseline subset algorithm and a time series analysis was achieved for two stacks of data sets. Considered alongside experimental results, this successful application demonstrates the feasibility of the proposed nonlocal method to facilitate the adoption of GBSAR for deformation monitoring applications.

Integration of Range Split Spectrum Interferometry and conventional InSAR to monitor large gradient surface displacements

Incorrect unwrapping of dense interferometric fringes caused by large gradient displacements make it difficult to measure mining subsidence using conventional Interferometric Synthetic Aperture Radar (InSAR). This paper presents a Range Split Spectrum Interferometry assisted Phase Unwrapping (R-SSIaPU) method for the first time. The R-SSIaPU method takes advantage of (i) the capability of Range Split Spectrum Interferometry of measuring surface displacements with large spatial gradients, and (ii) the capability of conventional InSAR of being sensitive to surface displacements with limited spatial gradients. Both simulated and real experiments show that the R-SSIaPU method can monitor large gradient mining-induced surface movements with high precision. In the case of the Tangjiahui mine, the R-SSIaPU method agreed with GPS with differences of approximately 4.2 cm, whilst conventional InSAR deviated from GPS with differences of nearly 1 m. The R-SSIaPU method makes phase unwrapping less challenge, especially in the cases with large surface displacements. In addition to mining subsidence, it is believed that the R-SSIaPU method can be used to monitor surface displacements caused by landslides, earthquakes, volcanic eruptions, and glacier movements.

Dynamic triggering of shallow slip on forearc faults constrained by monitoring surface displacement with the IPOC Creepmeter Array

The Mw=8.8 Maule Earthquake of February 27, 2010, remotely triggered minor surface displacement along the Atacama Fault System in Northern Chile located 1500–1800 km from the epicenter. Here we present evidence that surface displacement events recorded by the IPOC (Integrated Plate Boundary Observatory in N-Chile) Creepmeter Array are related to earthquakes on the underlying subduction zone interface or to large earthquakes around the world. Our observations document dynamic triggering of shallow slip on faults in a forearc setting. Continuous monitoring revealed that up to 30 displacement events per year occur on the monitored fault segments, >90% of them triggered by earthquakes in the near or far field synchronous to the passage of the seismic wave. We can clearly attribute far field triggering to the passage of the surface wave and near field triggering to the passage of the body wave. The most distant triggered displacement event monitored occurred after the 2011, Mw=9.0 Tohoku-Oki Earthquake located 16 468 km away following the passage of large amplitude SS waves. Comparing the triggered displacement events with other triggered phenomena like seismicity, volcanic eruptions, hydrological changes as well as with data from the California Creepmeter Array we find that the seismic energy density appropriately describes a magnitude–distance scaling relationship of slip triggering. Finally, the observed surface displacement is found to not occur by continuous creep, but rather through nearly exclusively discrete displacement events.

Quantitative Assessment of Digital Image Correlation Methods to Detect and Monitor Surface Displacements of Large Slope Instabilities

We evaluate the capability of three different digital image correlation (DIC) algorithms to measure long-term surface displacement caused by a large slope instability in the Swiss Alps. DIC was applied to high-resolution optical imagery taken by airborne sensors, and the accuracy of the displacements assessed against global navigation satellite system measurements. A dynamic radiometric correction of the input images prior to DIC application was shown to enhance both the correlation success and accuracy. Moreover, a newly developed spatial filter considering the displacement direction and magnitude proved to be an effective tool to enhance DIC performance and accuracy. Our results show that all algorithms are capable of quantifying slope instability displacements, with average errors ranging from 8 to 12% of the observed maximum displacement, depending on the DIC processing parameters, and the pre- and postprocessing of the in- and output. Among the tested approaches, the results based on a fast Fourier transform correlation approach provide a considerably better spatial coverage of the displacement field of the slope instability. The findings of this study are relevant for slope instability detection and monitoring via DIC, especially in the context of an ever-increasing availability of high-resolution air- and spaceborne imagery.

DIFFERENTIAL SAR INTERFEROMETRY TECHNIQUE FOR CONTROL OF LINEAR INFRASTRUCTURES AFFECTED BY GROUND INSTABILITY PHENOMENA

Abstract. The Italian territory is strongly affected by ground instability phenomena and the occurrence of geological events, such as landslides and subsidence, is one of the main causes of damage to linear infrastructures, such as roads, bridges, railways and retaining walls, resulting in important socio-economic and human losses. To this aim, the frequent and accurate monitoring of surface displacements plays a key role in risk prevention and mitigation activities. In the last decade, a considerable interest towards innovative approaches has grown among the scientific community and land management institutions. In particular, Differential Interferometry Synthetic Aperture Radar (DInSAR) technique represents a useful tool to provide information on temporal and spatial evolution both of ground instability phenomena and of their interaction with man-made facilities, thanks to its accuracy, high spatial resolution, non-invasiveness and long-term temporal coverage, at reasonable costs. In this work, a GIS-semiautomatic approach, using Synthetic Aperture Radar data acquired by COSMO-SkyMed sensor, has been successfully applied to detect landslide-induced effects in terms of deformations of a linear infrastructure interested by slow-moving landslides in Campania Region (Italy).