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Resolving three-dimensional surface displacements from InSAR measurements: A review
Abstract
One-dimensional measurement along the Line-Of-Sight (LOS) direction has greatly limited the capability of InSAR technique in the investigation of surface displacements and their dynamics. In recent years, great efforts have been made to resolve complete three-dimensional (3-D) displacements from InSAR measurements. This contribution is intended to provide a systematic review of the progress achieved in this field. Based on an analysis of the InSAR LOS measurements, we first cover two commonly used techniques, i.e., Offset-Tracking and multi-aperture InSAR (MAI), with which the surface displacement in the azimuth direction can be measured together with the LOS displacement. Several methods for mapping 3-D displacements using InSAR measurements are subsequently presented and categorized into three groups: (i) combination of multi-pass LOS and azimuth measurements; (ii) integration of InSAR and GPS data; and (iii) prior information assisted approaches. The strengths and weaknesses of each method are analyzed to show the applicability of each method to specific 3-D displacement mapping cases, in hope to provide a useful guidance in choosing a suitable approach accordingly. Finally, suggestions for resolving the challenging issues and outlook of future research are given.
... The 3-D displacement fields can theoretically be obtained by exploiting multiple DInSAR observations from at least three different radar look directions since the DInSAR-measured surface displacement is usually in the LOS direction (Hu et al. 2014). Therefore, we exploited Sentinel-1B and ALOS-2 DInSAR observations to produce the coseismic 3-D displacement fields of the earthquake. ...
... Therefore, we exploited Sentinel-1B and ALOS-2 DInSAR observations to produce the coseismic 3-D displacement fields of the earthquake. The coseismic 3-D displacements were determined as follows (Hu et al. 2014;Fuhrmann and Garthwaite 2019): ...
... where d E , d N , and d U are the displacement vector components in the E-W, N-S, and U-D directions, respectively, θ and α are the radar incidence angle and heading of the satellite, respectively, and d S dsc , d A dsc , and d A asc indicate the LOS displacements measured at the Sentinel-1B at descending, ALOS-2 at descending, and ALOS-2 at ascending paths, respectively. We determined the errors of the estimated 3-D displacements by InSAR pairs' incidence and heading angles and the precision of the displacements in the different LOS directions (He et al. 2019;Hu et al. 2014). The precision of the LOS displacement was estimated by calculating the mean and standard deviation values in the region with no coseismic surface displacement (He et al. 2019;Hu et al. 2014). ...
On 11 January 2021, an Mw 6.7 earthquake, which involved a complex rupture mechanism, occurred in Lake Hovsgol, Mongolia. This study measured the earthquake’s 3-D coseismic surface displacement fields using interferometric synthetic aperture radar (InSAR) pairs of three radar look directions: Sentinel-1B from the descending path and Advanced Land Observing Satellite-2 from the ascending and descending paths. The three DInSARs showed that the maximum coseismic surface displacement appeared east of the Northern Hovsgol Fault (NHF), where the displacement components were 18 cm, 5 cm, and 33 cm in the east–west, north–south, and up–down directions, respectively (precision: 1.7 cm, 20.4 cm, and 5.2 cm). However, the 3-D displacements indicated that although the earthquake induced a combination of normal faulting with strike slip motions, the displacements in the north–south direction had very large uncertainty owing to the similar geometry of the InSARs in the descending path. Later, we performed inversions of the DInSAR-measured coseismic surface displacement fields in the line-of-sight direction, which assumes a fault plane’s uniform and distributed slips in analyzing the slip mechanism. We conducted slip distribution estimations on the ruptured fault plane in accordance with the optimal fault geometry and source parameters determined by the uniform slip model. Investigations revealed that, with a correlation of 95.3%, the simulated displacements from the best-fitted distributed slip model were consistent with the observed displacements from DInSARs. Besides, our slip distribution model showed two distinctive slip patches, which include differences in their magnitudes and directions on the fault plane. We also observed ruptured faults experiencing a predominant right-lateral strike slip with a significant dip slip, according to the slip distribution, which caused two distinct slips due to the dramatic bending of the fault strike. Then, by analyzing the Coulomb stress change, our findings proposed that the seismic risk potential of active faults in the Hovsgol Basin increased after the earthquake. Overall, the great potential of multi-track DInSAR observations in the identification of complex slip mechanisms was demonstrated.
... Given the damages caused by landslides, it is essential to closely monitor the unstable slopes to reduce the risk of landslides. A way of monitoring unstable mountain slopes is via surface subsidence velocities, the rate of vertical movement of the Earth's surface downward, evaluated using the Interferometric Synthetic Aperture Radar (InSAR) technique [4]. InSAR technique has been applied at local scales to monitor surface movements and ground subsidence [4]- [8]. ...
... A way of monitoring unstable mountain slopes is via surface subsidence velocities, the rate of vertical movement of the Earth's surface downward, evaluated using the Interferometric Synthetic Aperture Radar (InSAR) technique [4]. InSAR technique has been applied at local scales to monitor surface movements and ground subsidence [4]- [8]. With the advent of the Sentinel satellite program, the InSAR technique has the advantage of open-source data availability, broad area coverage, good spatial and temporal resolution, and operation under all weather conditions [4]. ...
... InSAR technique has been applied at local scales to monitor surface movements and ground subsidence [4]- [8]. With the advent of the Sentinel satellite program, the InSAR technique has the advantage of open-source data availability, broad area coverage, good spatial and temporal resolution, and operation under all weather conditions [4]. The small baseline subset InSAR (SBAS-InSAR) and the permanent scatterer InSAR (PS-InSAR) are the most common InSAR methods [5]. ...
The Himalayan mountains are prone to landslide disasters, which cause injury and fatalities among people. Remote sensing, particularly interferometric synthetic aperture radar (InSAR) based analyses, may help find the surface subsidence velocities, the rate of vertical movement of the Earth's surface downward. These subsidence velocities may help identify areas prone to landslides. Literature suggests that geotechnical parameters may contribute to understanding surface subsidence velocities. However, there is less research on developing data-driven algorithms that relate the geotechnical parameters with the subsidence velocities in an area. In this research, data-driven algorithms, relying upon geotechnical parameters measured across diverse locations in the Himalayan mountains, predict the subsidence velocities measured from InSAR analysis of open-source Sentinel-1 data of the same area. An InSAR-based displacement map of the study area is generated using the Small Baseline Subset (SBAS) algorithm. The ranking of geotechnical parameters is first conducted using several feature selection methods. Out of 23 parameters, 11 top-ranked features are selected for developing data-driven algorithms, including multiple regression, random forest, instance-based learner, an optimized version of support vector regression named sequential minimal optimization regression (SMOreg), multilayer perceptron (MLP), and an ensemble of MLP and SMOreg (MLP-SMO). These algorithms used the top-ranked geotechnical parameters and predicted the subsidence velocities. Results suggested that the MLP-SMO algorithm provided the best fit for data in 10-fold cross-validation with 0.94 RMSE. The MLP was the second-best model with 1.6 RMSE. Implications for developing subsidence velocity models using geotechnical parameters via data-driven approaches are discussed.
... Interferometric Synthetic Aperture Radar (InSAR) is an active remote sensing technique used to create DEM and monitor surface deformation on a cm to mm scale accuracy (Hu et al. 2014). Synthetic Aperture Radar imaging systems work by transmitting an electromagnetic pulse from a sensor mounted on an aircraft or satellite to the Earth's surface, and Interferometry exploits the phase difference between two or more SAR images (Ferretti 2014). ...
... The standard InSAR technique for mapping ground movement is called differential InSAR (D-InSAR), which uses the repeat pass method to compare two or more SAR images taken over the same area at different times (Simons and Rosen 2007). Over the past three decades, more advanced multi-temporal InSAR (MT-InSAR) techniques have been developed, which use a network of interferograms rather than a single pair to reduce the spatial, temporal and atmospheric decorrelation, enhance the precision of ground deformation, and provide time series analysis (Hu et al. 2014;Osmanoğlu et al. 2016). The algorithms include the Permanent Scatterer InSAR (PS-InSAR; Ferretti et al. 2001;Ferretti 2014) and Small Baseline Subset (SBAS; Berardino et al. 2002;Ferretti 2014;Lanari et al. 2004;Yunjun et al. 2019) methods, and approaches which combine the two (Hu et al. 2014;Osmanoğlu et al. 2016) such as the Stanford Method for Persistent Scatterers (StaMPS; Hooper 2008) and SqueeSARTM (Ferretti et al. 2011). ...
... Over the past three decades, more advanced multi-temporal InSAR (MT-InSAR) techniques have been developed, which use a network of interferograms rather than a single pair to reduce the spatial, temporal and atmospheric decorrelation, enhance the precision of ground deformation, and provide time series analysis (Hu et al. 2014;Osmanoğlu et al. 2016). The algorithms include the Permanent Scatterer InSAR (PS-InSAR; Ferretti et al. 2001;Ferretti 2014) and Small Baseline Subset (SBAS; Berardino et al. 2002;Ferretti 2014;Lanari et al. 2004;Yunjun et al. 2019) methods, and approaches which combine the two (Hu et al. 2014;Osmanoğlu et al. 2016) such as the Stanford Method for Persistent Scatterers (StaMPS; Hooper 2008) and SqueeSARTM (Ferretti et al. 2011). The method depends on the data available, the study area and the information the user is trying to extract. ...
Landslides are widespread geomorphological features on the North Island of New Zealand, where they represent one of the primary landscape-forming processes. This study focuses on the steepland terrain surrounding Gisborne, a city located on the east coast of the North Island, at the Hikurangi subduction margin. This terrain consists of young, weak, sedimentary rocks and soils; the most common modes of slope failures are soil creep, slides and flows in shallow, clay-rich soil and regolith, triggered by heavy rainfall. Based on observational data from Sentinel-1 imagery, this study leverages results from interferometric synthetic aperture radar (InSAR) processing to reveal the distribution of deformation across Gisborne’s steepland periphery from January 2016 to December 2021. Velocities in the line of sight were obtained from the stack of interferograms and projected along the direction of maximum slope, to extract the true displacement on the slopes. The ascending and descending data sets were combined to reveal the vertical and horizontal components of the deformation. The results were combined with a regional LiDAR data set, aerial imagery and field observations to delineate areas of slope deformation. Finally, slope deformation time series data was compared with rainfall records to identify seasonal changes, due to shrinking and swelling of expansive soils. Although the InSAR displacement data contains some noise, results could be used to identify 132 unstable slopes within the study area, caused by soil creep and earthflows. Also, the shrink-swell of expansive soils causes a seasonal pattern of displacements, which varied by 10–20 mm/year between Austral winter and summer, strongly correlated to rainfall.
... As the LOS displacement represents only one-dimensional (1D) manifestation along the satellite viewing direction, it provides only limited constraints on the real pattern of crustal deformation (e.g., dextral or sinistral strike-slip, thrust or dip-slip) [23]. In this context, 2D (two-dimensional) displacement can improve our understanding of the characteristics of crustal deformation caused by the 2021 Mw 5.7 Nagqu earthquake. ...
... In this context, 2D (two-dimensional) displacement can improve our understanding of the characteristics of crustal deformation caused by the 2021 Mw 5.7 Nagqu earthquake. To this end, the 2D coseismic ground deformation fields are decomposed from the ascending and descending coseismic interferograms to better constrain the characteristics of the fault deformation [23]. The decomposed 2D displacements are characterized by southwest horizontal motion along the strike direction and subsidence in the northwestern lobe, and northeast horizontal motion along the strike direction and uplift in the southeast lobe ( Figure 3). ...
... scending coseismic interferograms to better constrain the characteristics of the fault deformation [23]. The decomposed 2D displacements are characterized by southwest horizontal motion along the strike direction and subsidence in the northwestern lobe, and northeast horizontal motion along the strike direction and uplift in the southeast lobe (Figure 3). ...
The Nyainrong microcontinent carries key information about the ongoing evolution of the central Tibetan Plateau. The 2021 Mw 5.7 Nagqu earthquake is the largest instrumentally recorded event inside this microcontinent, which provides an ideal opportunity to elucidate the influence of this ancient microcontinent on the seismogenic mechanisms, stress heterogeneity and strain partitioning across the Tibetan Plateau. Here, we constrain the seismogenic fault geometry and distributed fault slip using Interferometric Synthetic Aperture Radar (InSAR) observations. By using the regional focal mechanism solutions, we invert the stress regimes surrounding the Nyainrong micro-continent. Our analysis demonstrates that the mainshock was caused by a normal fault with a comparable sinistral strike-slip component on a North-West dipping fault plane. The Nyainrong microcontinent is surrounded by a dominant normal faulting stress regime to the northeast and a dominant strike-slip stress regime to the southwest. Moreover, the clockwise rotation of the maximum horizontal stress (SHmax) from the southwest to the northeast is ~20°. This indicates that the Nyainrong microcontinent is involved in the mainshock occurrence as well as regional stress heterogeneity, and strain partitioning. Our results highlight the significance of the ancient micro-continent in the tectonic evolution of the Tibetan Plateau.
... Therefore, in order to prevent the reduction of the effective observation area caused by topographic factors, the method of combining the ascending and descending Sentinel−1 data is adopted to effectively reduce the defects that cannot be effectively observed due to geometric distortion so as to improve the effective utilization of satellite data. In addition, in the deformation calculation of some areas, the combination of ascending and descending data can assist in verification or three-dimensional deformation calculation [33][34][35]. It can be seen from Figures 9 and 10 that it is difficult for single orbit data to comprehensively obtain deformation information in the study area. ...
... Therefore, in order to prevent the reduction of the effective observation area caused by topographic factors, the method of combining the ascending and descending Sentinel−1 data is adopted to effectively reduce the defects that cannot be effectively observed due to geometric distortion so as to improve the effective utilization of satellite data. In addition, in the deformation calculation of some areas, the combination of ascending and descending data can assist in verification or three-dimensional deformation calculation [33][34][35]. ...
Potential landslides in the mountainous areas of southwest China pose a serious threat to the lives and property of local residents. Synthetic aperture radar interferometry (InSAR) technology has the advantages of wide coverage, all weather applicability, and low cost and can quickly and accurately identify large range of active landslides, making it a useful geodetic tool for the early identification and prevention of landslides. This paper employed small baseline subset InSAR (SBAS−InSAR) technology and ascending and descending Sentinel−1 data from January 2019 to December 2021 to early identify active landslides in the Maoxian County to Li County National Highway (G317 and G213). The InSAR deformation results were verified by geometric distortion analysis, optical remote sensing interpretation, and field investigation, and 115 active landslides were successfully determined, among which 23 active landslides were identified by ascending and descending Sentinel−1 data together. In addition, InSAR deformation results show that fault, stratigraphic lithology, and rainfall are the three main factors that accelerate the deformation of active landslides and can trigger new active landslides. This study can provide an important reference for the early identification and prevention of landslides in mountainous areas.
... In the early years of InSAR, one viewing geometry was used for estimating displacements [2], [3], [4]. However, the possibility to combine ascending and descending orbits imaging the same area of interest triggered attempts to estimate the 3D displacement vectors [5], [6], [7], [8]. Evidently, to estimate the full 3D displacement vector, one would need three independent viewing geometries, using three different P LoS ⊥ projectors forming a full rank matrix with a low condition number [9]. ...
... In this study, we provide an overarching and rigid mathematical framework rooted in linear algebra, building on previous work by [1], [6], [7] and [8] (Sec. II), explicitly state the conditions for a successful inversion (Sec. ...
It is well known that InSAR phase observations are only sensitive to the projection of the 3D displacement vector onto the radar line-of-sight (LoS) direction. We require at least three LoS observations to uniquely estimate the three displacement components, and the system of equations needs to have a full rank coefficient matrix. Unfortunately, in many practical situations, only two LoS observations are available at most (i.e., ascendingand descending), resulting in an underdetermined system with an infinite amount of possible solutions. Yet, this has not prevented many authors from performing LoS decompositions that are fundamentally flawed. Starting with a mathematical framework based on linear algebra, we introduce the concept of the null line, the direction in which no displacements can be observed, and identify the strict criteria to perform decompositions and projections. We propose using a null-line aligned (NLA) referenceframe, which results in bias-free estimates. Based on a literature survey, we identify the most common flaws in handling 3D InSAR geometry, and develop a taxonomy to label different classes of fallacies. This work results in recommendations for a more optimal and uniform handling of InSAR geometry, in terms ofclaims and results.
... However, the landslide's evolution process is very complex, and its movement and displacement are often not in the LOS or azimuth directions. Therefore, observational results from a single direction are often not accurate enough to describe the landslide movement [23]. It is necessary to use multi-orbit SAR data to obtain three-dimensional deformation information on landslides through deformation data in three directions. ...
... Determining a movement situation in a single direction is difficult to grasp accurately with InSAR monitoring. The three-dimensional deformation field can derive from different directions of InSAR measurements [23,28]. The estimated 3-D displacements (du, de, and dn) and their variances ( , and ) were determined from three direction measurements (dlos,1, dlos,2 and dlos,3) and their errors ( , , and , ), as follows: ...
Many ancient landslides in the upper reaches of the Jinsha River seriously threaten the safety of residents on both sides of the river. The river erosion and groundwater infiltration have greatly reduced the stability of the ancient landslides along the Jinsha River and revived many large landslides. Studying their deformation characteristics and mechanisms and predicting possible failure processes are significant to the safety of residents and hydropower projects. We used SBAS-InSAR and three-dimensional decomposition techniques in our study. Our results showed that the trailing edge and middle part of the landslide have rapidly deformed. The maximum vertical annual displacement rate was 12 cm/a period from July 2017 to July 2019. Correlation analysis showed that creep deformation is closely related to the river damming of the Baige landslide events and that the rising river level was an important factor in the resurrection and accelerated destruction of the Xiaomojiu landslide. As a result, we predicted the possible failure process of the Xiaomojiu landslide, which might have lasted 80 s and eventually formed a landslide deposit with a height of about 150 m, a length of approximately 1500 m, and an average width of 450 m. Our results provide data references for displacement monitoring and instability risk simulation of large landslides along the Jinsha River.
... It should be emphasized that the horizontal direction was defined as the landslide sliding direction (slope−oriented) rather than the south−north or east-west direction. The two−dimensional displacement can be obtained by the following equation [24,36,37]. Further, the minimum cost flow algorithm was used to unwrap the differential interference phase, and the unwrapping phases were superimposed to obtain the average deformation rate of the study area [33]. ...
... It should be emphasized that the horizontal direction was defined as the landslide sliding direction (slope-oriented) rather than the south-north or east-west direction. The two-dimensional displacement can be obtained by the following equation [24,36,37]. ...
In recent years, due to adverse geological conditions, intense human engineering activities, and extreme weather conditions, catastrophic landslides have frequently occurred in southwest China, causing severe loss of life and property. Identifying the kinematic features of potential landslides can effectively support landslide hazard prevention. This study proposes a remote sensing identification method for rotational, planar traction, and planar thrust slides based on geomorphic features as well as vertical and slope-oriented deformation rates. Rotational landslides are characterized by similar vertical and horizontal deformation rates, with vertical deformation mainly occurring at the head and gradually decreasing along the slope, while horizontal deformation mainly occurs at the foot and gradually increases along the slope. As for the planar slide, the dominant deformation is in the horizontal direction. It is further classified into the planar traction and planar thrust types according to the driving position. The vertical deformation of planar traction slides is concentrated at the foot, while the vertical deformation of planar thrust slides is concentrated at the head of the landslide. We identified 1 rotational landslide, 10 planar traction landslides and 10 planar thrust landslides in the basalt weathering crust area of Guizhou. Field investigations of three landslides verified the method’s accuracy. Combining two-dimensional rainfall and time-series deformations, we found that there is a significant positive correlation between landslide deformation acceleration and precipitation. The landslide kinematic identification method proposed in this paper overcomes the shortcomings of the inability to accurately characterize landslide motion by line-of-sight displacement and realizes the non-contact identification of active landslide motion patterns, which is an essential reference value for geological disaster prevention and control in the study area.
... Apart from rare cases in which the targets move with a velocity parallel to the satellite look direction, a series of InSAR images from a single viewing geometry cannot fully capture the magnitude and direction of the real deformation, and for most of the cases the LOS displacements underestimate the real motion (Hu et al. 2014). This concept is illustrated in Figure 5-11, which shows a target moving along a direction close to the vertical ( Figure 5-11a), and a target with a dominant horizontal motion ( Figure 5-11b). ...
... Some of these problems can be mitigated through the use of multi-geometry/multiaperture and multi-sensor methods. These methods allow one to combine satellite data acquired from different viewing geometries, frequencies and incidence angles, while simultaneously allowing for the integration of external data sources such as GPS or precise levelling (Cuenca, Hanssen, Hooper & Arikan 2011, Fuhrmann et al. 2015, Hu et al. 2014. In contrast to the simple multi-geometry approach which can only provide deformation measurements in 2-D space, the combination of these methods can be used to reconstruct 3-D deformations from LOS MT-InSAR measurements. ...
The deterioration of ageing infrastructure assets and the risk of damaging surrounding structures during new construction are major concerns for the transport industry worldwide. Whilst, Structural Health Monitoring (SHM) could assist the lifecycle management of existing assets and the assessment of structures adjacent to large construction projects, the cost of sensors limits the number of structures that can be evaluated. Space-borne Interferometric Synthetic Aperture Radar (InSAR) is a powerful remote-sensing technology which can provide deformation measurements over time for numerous points located on buildings and infrastructure assets. Such measurements are available with an accuracy comparable to traditional in-situ monitoring devices, but at a much lower cost. Furthermore, due to the combination of wide area coverage and high spatial resolution, InSAR can easily shift from local to larger scale, with the potential to provide a cost-effective tool for SHM on a regional level. However, to assess the condition of a given structure, InSAR deformation measurements need to be translated into structural performance indicators. This requires an integration of InSAR displacement measurements and structural information and/or models. Such integration can be particularly demanding for regional analysis, where a vast number of structures needs to be evaluated.
The objective of this thesis is to develop a new methodology using InSAR data to
monitor and assess the conditions of buildings and infrastructure assets on a regional
scale. Such a methodology will allow the understanding of the long-term behaviour
of existing infrastructure, and the assessment of damage to existing structures caused
by new infrastructure construction. This involved: (i) the definition of performance
indicators for the identification of anomalous structural deformations on a large scale;
(ii) the integration of InSAR deformation measurements and structural models to
interpret the measured deformations in relation to a specific source of movement;
(iii) a clear definition of the InSAR challenges that still need to be overcome in order
to use the developed methodology as an operational SHM tool.
First, a new method using InSAR displacement measurements to evaluate the
condition of large transport networks was developed. The proposed method is based
on an automated workflow which enables the integration of InSAR deformation measurements and digital databases of roadway and bridge infrastructure to warn of potentially anomalous deformations within a given network. For each asset and roadway segment, the method allows the assessment of monitoring point density, the retrieval of local displacements and velocities, and the identification of anomalous relative movements within the same structure. The developed method provides output maps showing the distribution of PS density, local displacements, velocities and the locations of anomalies. The developed method was tested on the Los Angeles highway and freeway network and on the Italian motorway system, validating its performance from city to national scale. Furthermore, to show the capability of the proposed method of identifying potentially damaging movements, the case of an Italian motorway viaduct that was damaged in 2015 is presented.
Second, a new method using InSAR displacement measurements for the structural
assessment of buildings adjacent to tunnel excavations was developed. The proposed method is based on an automated workflow which enables the integration of InSAR deformation measurements, digital building databases and structural models
of the building response to tunnelling-induced settlements. InSAR displacement
measurements were used to estimate the settlement profile for each building. To
calculate critical strains for each building, building settlement profiles were analysed
through a semi-empirical model. On the basis of the estimated critical strain, a level
of damage was assigned to each building. The proposed method provides as outputs
damage maps showing the distribution of damage levels for the buildings along the
excavation. The developed method was tested on the buildings along the Crossrail
tunnel alignment in London, and enabled the identification of structural damage to
more than 800 buildings, highlighting its capability as a city-scale assessment tool.
The developed integration also provided the first large dataset of field information on
building response to tunnelling, enabling the identification of relationships between
structural characteristics and building responses.
Finally, based on the technical issues encountered during this research and the
open problems identified by other researchers, a discussion about the advances needed in InSAR technology to be used as a SHM tool was developed. In this discussion, each InSAR technological limitation was evaluated from a SHM perspective. The challenges that still need to be overcome to use InSAR as an operational tool were
defined, with examples showing the practical limitations of InSAR technology. Possible
solutions and promising research directions were also identified.
The proposed methodology has the potential to inform timely maintenance and
prioritisation decisions, and can complement in-situ monitoring instrumentation. Findings can improve current practice for condition monitoring and assessment on large scale, with the possibility to advance the understanding of structural deformation mechanisms.
... Furthermore, three-dimensional (3D) deformation fields can provide particular clues for understanding the type, failure mode, and subsurface sliding geometry of active landslides [22,29]. The 2D displacement field of the actively moving part of a landslide can be estimated by the SAR offset tracking method using single-orbit SAR data, thus making it possible to invert 3D displacements using SAR images from two or more observations with diverse imaging geometries [2,30]. However, multi-orbit satellite SAR observations are usually difficult to satisfy in most areas on Earth [11]. ...
... However, multi-orbit satellite SAR observations are usually difficult to satisfy in most areas on Earth [11]. Thus, another alternative solution for retrieving 3D deformation is to add a priori information of landslide movement to reduce the degrees of freedom [30], when only a single-orbit SAR dataset is available. In the case of landslides, an acceptable assumption is that landslides move parallel to their ground surface; thus, by adding a parallel displacement constraint to SAR offset measurements, the 3D displacements can be estimated. ...
Multi-dimensional, long-term time series displacement monitoring is crucial for generating early warnings for active landslides and for mitigating geohazards. The synthetic aperture radar (SAR) interferometry method has been widely applied to achieve small-gradient landslide displacement monitoring; however, measuring the landslide displacement with a steep gradient has posed certain challenges. In comparison, the SAR offset tracking method is a powerful tool for mapping large-gradient landslide displacement in both the slant-range and azimuth directions. Nevertheless, there are some limitations in the existing SAR offset tracking approaches: (i) the measurement accuracy is greatly reduced by the extreme topography relief in high mountain areas, (ii) a fixed matching window from expert experience is usually adopted in the calculation of cross-correlation, (iii) estimating the long-term displacements between the SAR images from cross-platforms and with longer spatiotemporal baselines is a challenging task, and (iv) it is difficult to calculate the three-dimensional (3D) landslide displacements using a single SAR dataset. Additionally, only a few studies have focused on how to realize early warning of landslide deformation using SAR measurements. To address these issues, this paper presents an improved cross-platform SAR offset tracking method, which can not only estimate high-precision landslide displacements in two and three dimensions but also calculate long-term time series displacements over a decade using cross-platform SAR offset tracking measurements. Initially, we optimize the traditional SAR offset tracking workflow to estimate high-precision ground displacements, in which three improvements are highlighted: (i) an “ortho-rectification” operation is applied to restrain the effect of topography relief, (ii) an “adaptive matching window” is adopted in the cross-correlation computation, and (iii) a new strategy is proposed to combine all the possible offset pairs and optimally design the displacement inversion network based on the “optimization theory” of geodetic inversion. Next, robust mathematical equations are built to estimate the two-dimensional (2D) and 3D long-term time series landslide displacements using cross-platform SAR observations. The M-estimator is introduced into the 2D displacement inversion equation to restrain the outliers, and the total least squares criterion is adopted to estimate the 3D displacements considering the random errors in both the design matrix and observations. We take the Laojingbian landslide, Wudongde Reservoir Area (China), as an example to demonstrate the proposed method using ALOS/PALSAR-1 and ALOS/PALSAR-2 images. The results reveal that the proposed method significantly outperforms traditional methods. We also retrieve the movement direction of each pixel of the Laojingbian landslide using the proposed method, thus allowing us to understand the fine-scale landslide kinematics. Finally, we capture and analyze the acceleration characteristics of the landslide, perform an early warning of hazard, and forecast the future displacement evolution based on the 3D displacement time series coupled with the physical models of the rocks.
... However, limited by the conditions of the ground receiving equipment, GNSS often has a very low spatial resolution [5]. On the other hand, InSAR can measure large-scale surface displacements with high spatial resolution and high accuracy [6]. However, InSAR can only provide deformation measured along the line of sight (LOS) between the Earth's surface and the radar. ...
... Then, we extend the above equation to the deformation in the east, north and up directions. The state equation can be generated by writing Equation (6) in matrix form. ...
This study proposes a new set of processing procedures based on the strain model and the Kalman filter (SM-Kalman) to obtain high-precision three-dimensional surface deformation time series from interferometric synthetic aperture radar (InSAR) and global navigation satellite system (GNSS) data. Implementing the Kalman filter requires the establishment of state and observation equations. In the time domain, the state equation is generated by fitting the pre-existing deformation time series based on a deformation model containing linear and seasonal terms. In the space domain, the observation equation is established with the assistance of the strain model to realize the spatial combination of InSAR and GNSS observation data at each moment. Benefiting from the application of the Kalman filter, InSAR and GNSS data at different moments can be synchronized. The time and measurement update steps are performed dynamically to generate a 3-D deformation time series with high precision and a high resolution in the temporal and spatial domains. Sentinel-1 SAR and GNSS datasets in the Los Angeles area are used to verify the effectiveness of the proposed method. The datasets include twenty-seven ascending track SAR images, thirty-four descending track SAR images and the daily time series of forty-eight GNSS stations from January 2016 to November 2018. The experimental result demonstrates that the proposed SM-Kalman method can produce high-precision deformation results at the millimeter level and provide two types of 3-D deformation time series with the same temporal resolution as InSAR or GNSS observations according to the needs of users. The new method achieves a high degree of temporal and spatial fusion of GNSS and InSAR data.
... Several algorithms of multi-temporal InSAR have been developed with time to create a continuous record of the displacement of SAR images in a specific time [29,30]. There are three basic categories based on the selection of master and slave selection [31]. The first technique PSI (or PS-InSAR), uses a single master image with multiple slaves to create interferograms. ...
Land subsidence is considered a threat to developing cities and is triggered by several natural (geological and seismic) and human (mining, groundwater withdrawal, oil and gas extraction, constructions) factors. This research has gathered datasets consisting of 80 Sentinel-1A ascending and descending SLC images from July 2017 to July 2019. This dataset, concerning InSAR and PS-InSAR, is processed with SARPROZ software to determine the land subsidence in Gwadar City, Balochistan, Pakistan. Later, the maps were created with ArcGIS 10.8. Due to InSAR's limitations in measuring millimeter-scale surface deformation, Multi-Temporal InSAR techniques, like PS-InSAR, are introduced to provide better accuracy, consistency, and fewer errors of deformation analysis. This remote-based SAR technique is helpful in the Gwadar area; for researchers, city mobility is constrained and has become more restricted post-Covid-19. This technique requires multiple images acquired of the same place at different times for estimating surface deformation per year, along with surface uplifting and subsidence. The InSAR results showed maximum deformation in the Koh-i-Mehdi Mountain from 2017 to 2019. The PS-InSAR results showed subsidence up to −92 mm/year in ascending track and −66 mm/year in descending track in the area of Koh-i-Mehdi Mountain, and up to −48 mm/year in ascending track and −32 mm/year in descending track in the area of the deep seaport. From our experimental results , a high subsidence rate has been found in the newly evolving Gwadar City. This city is very beneficial to the country's economic development because of its deep-sea port, developed by the China-Pakistan Economic Corridor (CPEC). The research is associated with a detailed analysis of Gwadar City, identifying the areas with significant subsidence, and enlisting the possible causes that are needed to be resolved before further developments. Our findings are helpful to urban development and disaster monitoring as the city is being promoted as the next significant deep seaport with the start of CPEC.
... Moreover, InSAR technique can only capture 1D surface displacement along the line-ofsight (LOS) direction. When earthquakes do not rupture the surface, it is hard to identify fault trace and even the dipping direction from a " visually deceptive" 1D displacement because reported cases revealed that different mechanisms can cause the same 1D LOS displacements [7,8]. The issues mentioned above can be potentially solved using multidimensional deformations [9][10][11][12][13]. ...
Pioneering efforts well studied the deformation decomposition of single earthquake using a pair of ascending (ASC) and descending (DES) track InSAR data. However, deformation decomposition of sequent events is rarely discussed and hard to implement. That's because it's hard to ensure deformations related to each earthquake can be recorded by a pair of ASC and DES track data. Three sequent earthquakes (Mw>5.5) just hit Central Greece in March 2021, and this earthquake sequence provides us with a perfect case to study 2D (East-West and Up-Down) deformation decomposition when the mentioned premise cannot be satisfied. In this context, we proposed a Multi-track and Multi-temporal 2D (MTMT2D) method. Its novelty and behind rationale are to decompose 2D deformations of each event through fusing multi-track and multi-temporal interferograms. Based on the decomposed deformations, we invert the slip distribution of three earthquakes respectively. We found that the decomposed deformations can better constrain the fault geometry than the single InSAR interferogram. Furthermore, our geodetic inversion results also suggest a domino-like triggering rupture process for this earthquake sequence. It indicates that our MTMT2D method can potentially reveal more details about earthquake sequence.
... Particularly, interferometric SAR (InSAR) has been widely applied to identifying landslides and monitoring slope surface displacements (Costantini et al., 2017;Herrera et al., 2013;Li et al., 2020;Rosi et al., 2017;Zhao et al., 2012). The line-of-sight (LOS) displacements derived from multi-track InSAR observations have also been combined to estimate slope-paralleled Wasowski and Bovenga, 2014) and three-dimensional (3D) displacements (Hu et al., 2014). ...
The Zhouqu County of Gansu Province in northwestern China is a geological hazard-prone area with frequent landslide and debris flow events. As a recent example, the Jiangdingya landslide, a smaller landslide within the larger ancient Nanyu landslide, was reactivated and partially collapsed to block the Bailong River near the Nanyu Township on July 12th 2018. Previous studies have shown that heavy rainfall is the major triggering factor of the failure event, but the spatio-temporal pattern of surface displacements of the landslide remains unknown due to a lack of in-situ measurements on the slope. In this study, we retrieved the surface displacements of the Nanyu landslide before the slope failure event using time-series Synthetic Aperture Radar Interferometry (InSAR) analysis of Sentinel-1 and ALOS-2 PALSAR-2 data. Our results show that the ancient Nanyu landslide has been in an unstable state prior to the failure event. To investigate the spatial patterns in displacement, we inverted a quasi three-dimensional (3D) surface displacement field using multi-orbit InSAR measurements combined with the surface parallel flow model, which showed a significant spatial heterogeneity in displacement patterns across the ancient landslide. In particular, a sign of reactivation was observed on the upper slopes, which might be related to local road construction. Furthermore, the detectability of unstable slopes near the Nanyu landslide with Sentinel-1 and ALOS-2 PALSAR-2 observations was analyzed to deepen our knowledge on the optimal choice of SAR data for geohazards detection and monitoring.
... InSAR measurements of the ground surface displacement are inherently one-dimensional (1D) in the line-of-sight (LOS) direction [14]. Thus, to obtain the 2D (east-west and up-down) or 3D (east-west, south-north, and up-down) or only up-down displacement fields, several approaches have been proposed to combine LOS observations from ascending and descending orbits and/or with other datasets (e.g., [15]). Examples include combining LOS measurements with (i) azimuth offset tracking [16][17][18][19][20][21], (ii) the direction of displacement field [22,23], (iii) Global Navigation Satellite System (GNSS) observations [24][25][26][27][28][29], (iv) incorporating prior deformation models [30]. ...
The availability of Synthetic Aperture Radar (SAR) data from different sensors and observation of the Global Navigation Satellite System (GNSS) has been growing worldwide. The complementary nature of InSAR and GNSS observations demands methodological advancements for integrating these datasets of variable accuracy, spatiotemporal sampling rate, and geometries to generate seamless maps of 3D time series that account for both observations advantages. Here, I present an approach based on Kalman Filter, which recursively resolves the 3D displacement field time series by combining line-of-sight time series from at least one SAR viewing geometry and horizontal velocities from GNSS networks. I apply this method to 3 overlapping SAR frames in ascending and descending orbits of Envisat C-band and ascending orbit of ALOS L-band acquired over the San Francisco Bay Area from 2007 to 2011. The experimental results and validation tests against independent observations indicate that the presented approach can resolve 3D displacement field time series at mm-level accuracy comparable to GNSS accuracy but at 10s m spatial resolution.
... After multiple MTI results are derived from various SAR datasets, we resolve the horizontal and vertical deformation with the weighted least squares (WLS) method following the equation (Fuhrmann and Garthwaite, 2019;Hu et al., 2014): ...
... As the imaging direction of the satellite is in the LOS direction, and the InSAR results in NLJL were only available in descending orbit SAR data (Hu et al., 2014a), InSAR results and GNSS results cannot be compared with high accuracy. However, we can still judge the reliability of InSAR results by comparing the magnitude with GNSS. Figure 6 shows a step in GNSS data from 2014 to 2015. ...
After the first impoundment of the reservoir, many landslides seriously threatened the safety of the reservoir. Accurate determination of the relationship between the landslide deformation characteristics and water-level fluctuations is crucial. However, with the increasing number of water-level fluctuation cycles, the deformation characteristics of the landslides were also changing, and long-term continuous monitoring to capture the failure process of reservoir landslides is necessary. A large reacted landslide in the Xiluodu reservoir was set as an example, using InSAR technology to seek its variations of deformation characteristics over nine years. The local deformation rate and annual maximum deformation area variation were analyzed by InSAR technology based on Sentinel-1 descending SAR data from October 2014 to June 2022. According to the regional deformation characteristics, the landslide was divided into three zones: Zone I above the elevation of 950 m; Zone II below it; the front edge of Zone II, where the collapse happened, was further divided into Zone III. In general, the accumulated deformation in Zone I was the largest, followed by Zone III, and Zone II was the smallest. The average deformation rate of Zone II was the smallest. Zone I of NLJL was mainly affected by the drawdown of reservoir water level, and the impacts of water-level rising and drawdown on Zone II and Zone III were similar. After analyzing a nine-year variation of the deformation area, the deformation mechanism of NLJL changed from a retrogressive type to a progressive one after the first impoundment and then changed back to a retrogressive one after 2017. The impact of reservoir impoundment on NLJL was most substantial in the first three years after the first impoundment.
... This limitation can be overcome when multiple datasets acquired with different viewing directions over the same area are available. We can retrieve the vertical and horizontal components of real deformation by combining LOS velocities obtained from ascending and descending viewing geometries [31][32][33]. For satellite-based InSAR, the various LOS still lie within a single plane, limiting the ability to resolve the true movement direction. ...
The Himalayan state of Sikkim is prone to some of the world's largest landslides, which have caused catastrophic damage to lives, properties, and infrastructures in the region. The settlements along the steep valley sides are particularly subject to frequent rainfall-triggered landslide events during the monsoon season. The region has also experienced smaller rock slope failures (RSF) after the 2011 Sikkim earthquake. The surface displacement field is a critical observable for determining landslide depth and constraining failure mechanisms to develop effective mitigation techniques that minimise landslide damage. In the present study, the persistent scatterers InSAR (PSI) method is employed to process the series of Sentinel 1-A/B synthetic aperture radar (SAR) images acquired between 2015 and 2021 along ascending and descending orbits for the selected areas in Gangtok, Sikkim, to detect potentially active, landslide-prone areas. InSAR-derived ground surface displacements and their spatio-temporal evolutions are combined with field investigations to better understand the state of activity and landslide risk assessment. Field investigations confirm the ongoing ground surface displacements revealed by the InSAR results. Some urban areas have been completely abandoned due to the structural damage to residential housing, schools, and office buildings caused by displacement. This paper relates the geotechnical investigations carried out on the ground to the data obtained through interferometric synthetic aperture radar (InSAR), focusing on the triggering mechanisms. A strong correlation between seasonal rainfall and landslide acceleration, as well as predisposing geological-structural setting, suggest a causative mechanism of the landslides.
... The InSAR measures a one-dimensional deformation along the line of sight (LOS) direction, and such measurements can lead to misinterpretation, as the true deformations may consist of horizontal and vertical displacements [30]. As is known, the LOS deformation is the sum of projection results of horizontal (including north-south and east-west components) and vertical displacement in the LOS direction. ...
The construction of large-scale hydropower stations could solve the problem of China’s power and energy shortages. However, the construction of hydropower stations requires reservoir water storage. Artificially raising the water level by several tens of meters or even hundreds of meters will undoubtedly change the hydrogeological conditions of an area, which will lead to surface deformation near the reservoir. In this paper, we first used SBAS-InSAR technology to monitor the surface deformation near the Xiluodu reservoir area for various data and analyzed the surface deformation of the Xiluodu reservoir area from 2014 to 2019. By using the 12 ALOS2 ascending data, the 100 Sentinel-1 ascending data, and the 97 Sentinel-1 descending data, the horizontal and vertical deformations of the Xiluodu reservoir area were obtained. We found that the Xiluodu reservoir area is mainly deformed along the vertical shore, with a maximum deformation rate of 250 mm/a, accompanied by vertical deformation, and the maximum deformation rate is 60 mm/a. Furthermore, by analyzing the relationship between the horizontal deformation sequence, the vertical deformation sequence, and the impoundment, we found the following: (1) Since the commencement of Xiluodu water storage, the vertical shore direction displacement has continued to increase, indicating that the deformation caused by the water storage is not due to the elastic displacement caused by the load, but by irreversible shaping displacement. According to its development trend, we speculate that the vertical shore direction displacement will continue to increase until it eventually stabilizes; (2) Vertical displacement increases rapidly in the initial stage of water storage; after two water-storage cycles, absolute settlement begins to slow down in the vertical direction, but its deformation still changes with the change in the storage period.
... Several studies have focused on and highlighted the various techniques for producing land subsidence data using DInSAR. Co-registration, Enhanced Spectral Diversity (ESD), Interferogram Formation (with Topographic Phase Removal or in a separate stage), Deburst, Filtering, Phase Unwrapping, Phase Deformation Retrieval, and Geocoding are the key data processing steps [12], [17]. ...
Considering the plan for achieving Sustainable
Development Goals, identifying the area that possesses
unsuitable for further development is mandatory, especially
when the area is vulnerable or threatened by a natural disaster
such as land subsidence in the coastal area. In basic terms, this
study focuses on updating the current information related to the
land subsidence and implementing the suitability assessment for
future development with the case study in Semarang City,
Central Java, where land subsidence is troublesome and
generating chain problem like tidal flood and saltwater
intrusion. This study uses several satellite imageries as
databases, such as Sentinel-1 and Sentinel-2, with different
target analyses and GIS methods to process and analyse the data
such as generating subsidence value and identifying surface
condition. The radar-based data of Sentinel-1 for processing
into the Differential Interferometry Synthetic Aperture Radar
(DInSAR) is essential to give a brief condition of land subsidence
underneath this area in 2022 with the vertical displacement
analysis capability. The result illustrates the displacement
change over time and is not always linear in each range, ranging
from -0.068 to 0.081 m, based on six raw radar-based and five
interferometry data collected from January to March. The extra
optical-based satellite images Sentinel-2 data is then utilized to
map the artificial feature and spread it out, especially buildings
with Built-up Index (BU). Each piece of information was
considered an integrated dataset overlapped to generate a
suitability map and indicate the region that is judged safe for
continued development, while also considering the geo�hydrological dataset and backed by ground checks. This
outcome will be discussed with the component that can aid
future sustainable development
... InSAR technology uses the phase difference between multiple SAR images acquired at different times in the same area to measure the ground motion occurring in the time interval (Hu et al., 2014). The results of surface deformation during CO 2 injection in the study area were obtained by combining InSAR with UAV technology. ...
Among CCUS methods, carbon dioxide-enhanced coalbed methane (CO2-ECBM) is one of the most important applications. The CO2 migration range in the reservoir and impact on the fractures are the keys to safe storage. Multiple geophysical methods of time-lapse DAS-VSP, passive microseismic, and InSAR have been taken to monitor the CO2-ECBM project in Shizhuang Town, Shanxi Province, China. The time-lapse DAS-VSP technology captures the changes of seismic amplitude due to CO2 injection. Three phases of passive microseismic monitoring detected 217 microseismic events and 48 earthquakes. Based on the distribution of the microseismic events, the CO2 migration direction was inferred to be northeast of the injection well. A quantitative calculation method for the impact of natural earthquakes on the storage site was proposed. Studies on the relationship between microseismicity and earthquakes suggest that natural earthquakes do not significantly affect CO2 storage in the study area. InSAR combined unmanned aerial vehicle (UAV) photography measurement technology obtained the surface deformation results with a maximum displacement of 21 mm. The surface deformation also shows CO2 migration in a northeast direction, consistent with microseismic results. Finally, in order to verify the monitoring results of the above methods, the gas detection in the production well around the injection site was analyzed. The analysis results show that the primary direction of CO2 migration in the study area is the northeast direction, followed by the east direction. These geophysical techniques validate the accuracy of the monitoring results and provide new technical support for future CCUS projects.
... After multiple MTI results are derived from various SAR datasets, we resolve the horizontal and vertical deformation with the weighted least squares (WLS) method following the equation (Fuhrmann and Garthwaite, 2019;Hu et al., 2014): ...
Using SAR and InSAR technology, artificial corner reflectors (CR) are popular coherent targets for monitoring ground instability with sub-centimeter accuracy in non-urban areas. In this letter, we investigate the performance of a newly designed small dihedral corner reflector for monitoring post-failure creep at the Aniangzhai landslide in Danba County, China. The new double geometry CRs consist of two sets of semi-circular metal plates, each 30-40 cm in radius and perpendicular to each other. Six such CRs are installed for Corner Reflector Interferometric SAR (CR-InSAR) analysis using both TerraSAR-X (TSX) High-resolution Spotlight (HS) data and medium-resolution Sentinel-1 (S1) SAR images. The CRs are first identified in SAR images using a probability model by taking into three factors. These are (1) inverse of amplitude dispersion, (2) intensity increment after the installation, (3) an upper empirical bound derived from the ensemble average of pixel intensities in post-deployment SAR images. Experimental results show that the CRs improve the background intensity in TSX images by around 30 dB, with signal-to-clutter ratio (SCR) exceeding 25 dB. Furthermore, the radar cross-section (RCS) of CRs in both TSX and S1 images remains relatively stable, ranging from 15 dB to 23 dB, making them suitable for CR-InSAR analysis using double-difference phase observations.
... However, the monitoring accuracy obtained by POT and MAI is only sufficient for application to large-gradient deformation monitoring (Fan et al. 2015). Multi-dimensional deformation can also be inferred by combining heterogeneous observational data such as the global satellite navigation system (GNSS) and InSAR (Hu et al. 2014) or exploiting prior knowledge of deformation processes (Ao et al. 2019) or specific geophysical models . However, the application of these methods is often limited by the lack of ground measurement data or poor availability of prior knowledge (Samsonov 2019). ...
The Lashagou landslide group in Gansu Province, China, is a typical shallow loess landslide group caused by artificial slope cutting. In April 2018, local sliding of the landslide group damaged houses and blocked the G310 highway, leading to the relocation of the Lashagou village, which aroused widespread concern. Unfortunately, the spatiotemporal displacement characteristics and failure modes of the landslide remain unknown. In this study, a method for the estimation of two-dimensional deformation of landslides, based on the local parallel flow model, was presented. This method only needs two orbital synthetic aperture radar (SAR) images with different imaging geometries, and has high accuracy verified by global satellite navigation system (GNSS) observations. In practice, we first obtained the surface velocity and time series deformation of the ascending and descending orbits. The best-fit sliding direction and inclination of the landslide movement were then inverted by combining satellite imaging geometry and surface velocity. Furthermore, the two-dimensional deformation of the Lashagou landslide group in the sliding and normal directions was obtained. We found that the landslide was in the accelerated deformation stage during the wet season and the deformation was mainly concentrated in the northern part of the Lashagou village. The snowmelt and continuous rainfall were the main factors in the landslide deformation. In addition, the landslide surface displacement characteristics and deep stress states can be linked using a combination of two-dimensional deformation, combined deformation, and inclination, which provides evidence that landslide movement is controlled by one or more deep continuous structural planes. Our research shows that the two-dimensional deformation retrieval method can be applied to gravity-driven translational landslides to help prevent and mitigate landslide hazards.
... Studies have shown that the change of aquifer head is coupled with ground subsidence (Chen et al., 2016b;Hoffmann 2003;Miller et al., 2017), which makes us more interested in the vertical observation from InSAR. However, the InSAR monitored deformation is the projection of the three-dimensional (3-D) surface deformation of vertical (d U ), east--west (d E ) and north-south (d N ) directions into LOS direction (d LOS ) (Hu et al., 2014), i.e., ...
Groundwater is the main water source for agricultural irrigation in arid/semi-arid agricultural region. Overexploitation of groundwater inevitably leads to permanent loss of aquifer and ground subsidence. The oasis agricultural area in the southern Junggar basin (JSOAA) is one of the largest oasis agricultural areas in western China. In this study, we, for the first time, recover the regional-scale ground displacements time-series of JSOAA, using all ALOS-1/PALSAR (2007 - 2010) and Sentinel-1 (2015 - 2020) data. The results show that there are multiple subsidence areas related to groundwater overexploitation. From 2007 to 2010, the area with a subsidence rate greater than 10 mm/yr is about 5876.2 km², accounting for 13.2% of the total area of JSOAA. From 2015 to 2020, these values are about 16146.7 km² and 36.3%. In the areas with concentrated groundwater exploitation, the small separate subsidence areas grew larger and became connected, and finally developed into giant subsidence clusters. The maximum cumulative deformation of JSOAA exceeded 400 mm from 2007 to 2010, and 500 mm from 2015 to 2020. We modeled the surface subsidence caused by the permanent aquifer loss, and estimated the volume strain of aquifer in JSOAA. The total volume strain of the aquifer is 2.73 km³ between 2007 and 2020. Moreover, we estimated the aquifer storage coefficient and the net groundwater deficit of JSOAA. The results of this study will serve for JSOAA aquifer health detection, ecological environment stability assessment, and sustainable development of the agricultural economy.
... Differential InSAR (D-InSAR) technique can only measure the LOS displacement at the surface, which is insensitive to the N-S component. For strike-slip faulting with a predominant N-S component, the InSAR-derived observations have weak constraint on the N-S component, leading to large uncertainties in the kinematic inversion results [8,9]. Azimuth displacements derived by burst overlap interferometry (BOI) provide good constraints on the N-S component and compensate for the insensitivity of InSAR-derived LOS displacements in this direction. ...
The azimuth displacement derived by pixel offset tracking (POT) or multiple aperture InSAR (MAI) measurements is usually used to characterize the north-south coseismic deformation caused by large earthquakes (M > 6.5), but its application in the source parameter inversion of moderate-magnitude earthquakes (~M 6.0) is rare due to the insensitive observation accuracy. Conventional line-of-sight (LOS) displacements derived by the Interferometric Synthetic Aperture Radar (InSAR) have limited ability to constrain the source parameters of the earthquake with near north-south striking. On 21 May 2021, an Mw 6.1 near north-south striking earthquake occurred in Yangbi County, Yunnan Province, China. In this study, we derive both the coseismic LOS displacement and the burst overlap interferometry (BOI) displacement from the Sentinel-1 data to constrain the source model of this event. We construct a single-segment fault geometry and estimate the coseismic slip distribution by inverting the derived LOS and BOI-derived azimuth displacements. Inversion results show that adding the BOI-derived azimuth displacements to source modeling can improve the resolution of the slip model by ~15% compared with using the LOS displacements only. The coseismic slip is mainly distributed 2 to 11 km deep, with a maximum slip of approximately 1.1 m. Coulomb stress calculation shows a maximum Coulomb stress increment of ~0.05 Mpa at the north-central sub-region of the Red River Fault. In addition, there is a small Coulomb stress increase at the Southern end of the Weixi-Weishan fault. The potential seismic risks on the Weixi-Weishan and Northwest section of the Red River faults should be continuously monitored.
... We thus obtained two range offset maps for the T033D and T128A SAR image pairs ( Fig. 2a,b) and east-west and north-south offset displacement component maps from the optical image pairs (Fig. 2c,d). We estimated the precision of these offset observations by choosing several regions of interest with negligible coseismic deformation and calculating the corresponding mean values and standard deviations ( Fig. S1; Table S1, available in the supplemental material to this article) (Hu et al., 2014). Then, the interferometric SAR (InSAR) method was used to process the SAR images to determine the fine detailed displacement information in the line of sight (LOS) (i.e., at the centimeter level) . ...
On 8 January 2022, an Mw 6.6 earthquake occurred along the Lenglongling fault (LLLF) (Menyuan, Qinghai Province, China), in the northeast margin of the Tibetan plateau. Here, we use imaging geodesy observations from pixel-offset tracking (POT) and Interferometric Synthetic Aperture Radar (InSAR) to quantify the coseismic displacement features and then combine InSAR and teleseismic velocity waveforms to constrain a finite-fault model to examine the kinematic slip behavior of the LLLF. We observe maximum displacements of >50 cm in the line-of-sight InSAR observations and >1 m in the east–west POT observations. Our preferred uniform-slip model indicates that the causative fault of this 2022 event ruptured the middle segment of the Qilian–Haiyuan fault (i.e., the LLLF) with a strike of 108.0°, a dip angle of 83.6°, and slip concentrated within a 15×8 km2 area and reaching a maximum value of 4 m. The total scalar seismic moment was 1.24×1019 N·m, and ∼67% of the energy was released in the first 6 s. We speculate that the 2022 event was controlled by complex fault geometries and slip partitioning, thus raising potential seismic risks associated with the outward extrusion of the plateau.
... [4] methods, providing sufficient displacement observations for measuring co-seismic 3D displacements. Although it is feasible to obtain co-seismic 3D displacements by combining DInSAR-derived line-of-sight (LOS) observations and POT/MAI/BOI-derived azimuth observations from ascending and descending SAR data [5][6][7][8], these kinds of methods are not suitable to calculate 3D displacements for small-magnitude earthquakes since the accuracy of POT/MAI/BOI observations is too low to derive reliable azimuth displacements [3,9,10]. ...
As one of the most prevailing geodetic tools, the interferometric synthetic aperture radar (InSAR) technique can accurately obtain co-seismic displacements, but is limited to the one-dimensional line-of-sight (LOS) measurement. It is therefore difficult to completely reveal the real three-dimensional (3D) surface displacements with InSAR. By employing azimuth displacement observations from pixel offset tracking (POT) and multiple aperture InSAR (MAI) techniques, 3D displacements of large-magnitude earthquakes can be obtained by integrating the ascending and descending data. However, this method cannot be used to accurately realize the 3D surface displacement measurements of small-magnitude earthquakes due to the low accuracies of the POT/MAI-derived azimuth displacement measurements. In this paper, an alternative method is proposed to calculate co-seismic 3D displacements from ascending and descending InSAR-LOS observations with the dislocation model-based displacement direction constraint. The main contribution lies in the two virtual observation equations that are obtained from the dislocation model-based forward-modeling 3D displacements, which are then combined with the ascending/descending InSAR observations to calculate the 3D displacements. The basis of the two virtual observation equations is that the directions of the 3D displacement vectors are very similar for real and model-based 3D displacements. In addition, the weighted least squares (WLS) method is employed to solve the final 3D displacements, which aims to consider and balance the possible errors in the InSAR observations as well as the dislocation model-based displacement direction constraint. A simulation experiment demonstrates that the proposed method can achieve more accurate 3D displacements compared with the existing methods. The co-seismic 3D displacements of the 2020 Nima earthquake are then accurately obtained by the proposed method. The results show that co-seismic displacements are dominated by the vertical displacement, the magnitude of the horizontal displacement is relatively small, and the overall displacement pattern fits well with the tensile rupture.
... We decompose the quasi-2D (two-dimensional) coseismic ground deformation fields from the ascending and descending coseismic interferograms, neglecting the North-South motions due to their much smaller contribution to the LOS compared to the East-West and Up-Down components (Hu et al., 2014). The decomposed 2D displacement maps show that the coseismic ground deformation is dominated by vertical displacements (Figure 5), which is consistent with the inverted relatively steep dip angle of the coseismic rupture. ...
Knowledge of the fault kinematics underlying the Papuan Fold Belt is important for better understanding the evolution of the orogen, but the active and long‐term tectonics of the region remain widely debated. The 2018 Mw 7.5 Papua New Guinea earthquake provides an unprecedented opportunity to probe the active fault structure deep in the Papuan Fold Belt. Here, we use Interferometric Synthetic Aperture Radar data from four ALOS‐2 acquisitions to study coseismic and postseismic ground deformation and invert for fault slip models. The results show that the oblique reverse earthquake reactivated a flat‐ramp structure and ruptured through most of the crust with the majority of coseismic slip confined between 5 and 25 km. Additionally, we found three separated postseismic slip zones with variable spatial complementarity between coseismic and postseismic slip, dip‐slip/strike‐slip ratio, and seismic/aseismic budget at three separated postseismic slip zones. Our results demonstrate that thick‐skinned tectonics dominate the current state of Papua New Guinea frontal orogen evolution.
... This approach produces highly accurate spatially dense deformation fields [11]. Line of sight (LOS) measures are only sensitive in one dimension and cannot determine the total co-seismic surface deformation [12]. The MAI interferometry approach was recently used to detect the deformation along the azimuth direction. ...
On 12 November 2017, an earthquake occurred in Sarpol Zahab city, located on the
Iraq/Iran boundary, with a moment magnitude (Mw) of 7.3. Advanced Land Observing Satellite 2 (ALOS-2) L-band (23.6 cm wavelength) and C-band Sentinel-1A data (ascending and descending) were used to detect the co-seismic displacements maps caused by this earthquake. The ALOS-2 data was utilized to reconstruct the 3D co-seismic displacements maps and estimate the fault-dip and slip distribution along the rupture. The results showed the maximum surface displacement in the
north, east, and up directions to be 100, 50, and 100 cm, respectively. The best-fit faulting geometry had a strike of 337.5◦ and a dip of 11.2◦ toward the northeast, at a depth of 8 km. The predicted geodetic moment was 1.15 1020 Nm, corresponding to a magnitude of Mw 7.31. There were two significant slip sources: one in the shallower depth range of 8.5–10 km, with a peak slip of 5 m, and another in the depth range of 10.5–20 km, with a peak slip of 5.3 m. Both controlled the principal deformation signals in geodetic images. The slip was concentrated, along with a strike distance of 20 to 40 km, at a depth of 10 to 20 km. The earthquake was caused by the Zagros Mountains Front Fault (ZMFF), based on the results of 3D co-seismic deformation, inferred slip, preliminary investigation, and interpretation of the mainshock, as well as aftershock distributions.
... This approach produces highly accurate spatially dense deformation fields [11]. Line of sight (LOS) measures are only sensitive in one dimension and cannot determine the total co-seismic surface deformation [12]. The MAI interferometry approach was recently used to detect the deformation along the azimuth direction. ...
On 12 November 2017, an earthquake occurred in Sarpol Zahab city, located on the Iraq/Iran boundary, with a moment magnitude (Mw) of 7.3. Advanced Land Observing Satellite 2 (ALOS-2) L-band (23.6 cm wavelength) and C-band Sentinel-1A data (ascending and descending) were used to detect the co-seismic displacements maps caused by this earthquake. The ALOS-2 data was utilized to reconstruct the 3D co-seismic displacements maps, as well as estimate the fault-dip and slip distribution along the rupture. The results showed the maximum surface displacement in the north, east, and up directions to be 100, 50, and 100 cm, respectively. The best-fit faulting geometry had a strike of 337.5° and a dip of 11.2° toward the northeast, at a depth of 8 km. The predicted geodetic moment was 1.15 1020 Nm, which corresponds to a magnitude of Mw 7.31. There were two significant slip sources: one in the shallower depth range of 8.5–10 km, with a peak slip of 5 m, and another in the depth range of 10.5–20 km, with a peak slip of 5.3 m. Both controlled the principal deformation signals in geodetic images. The slip was concentrated, along with a strike distance of 20 to 40 km, at a depth of 10 to 20 km. The earthquake was caused by the Zagros Mountains Front Fault (ZMFF), based on the results of 3D co-seismic deformation, inferred slip, preliminary investigation, and interpretation of the mainshock, as well as aftershock distributions.
... Advanced microwave remote sensing technology can precisely monitor deformation over wide areas, which helps geohazard surveys of phenomena such as underground fluid development, mineral mining, and landslide. In recent years, fast-developing interferometric synthetic aperture radar (InSAR) technology and abundant available synthetic aperture radar (SAR) data [1][2][3][4] has laid the foundation for high-precision and wide-scale InSAR ground-deformation monitoring. InSAR technology has been successfully used to monitor ground deformation at a regional [5][6][7][8][9] and national scale [10][11][12][13]. ...
In recent years, increasing available synthetic aperture radar (SAR) satellite data and gradually developing interferometric SAR (InSAR) technology have provided the possibility for wide-scale ground-deformation monitoring using InSAR. Traditionally, the InSAR data are processed by the existing time-series InSAR (TS–InSAR) technology, which has inefficient calculation and redundant results. In this study, we propose a wide-area InSAR variable-scale deformation detection strategy (hereafter referred to as the WAVS–InSAR strategy). The strategy combines stacking technology for fast ground-deformation rate calculation and advanced TS–InSAR technology for obtaining fine deformation time series. It adopts an adaptive recognition algorithm to identify the spatial distribution and area of deformation regions (regions of interest, ROI) in the wide study area and uses a novel wide-area deformation product organization structure to generate variable-scale deformation products. The Turpan–Hami basin in western China is selected as the wide study area (277,000 km2) to verify the proposed WAVS–InSAR strategy. The results are as follows: (1) There are 32 deformation regions with an area of ≥1 km2 and a deformation magnitude of greater than ±2 cm/year in the Turpan–Hami basin. The deformation area accounts for 2.4‰ of the total monitoring area. (2) A large area of ground subsidence has occurred in the farmland areas of the ROI, which is caused by groundwater overexploitation. The popularization and application of facility agriculture in the ROI have increased the demand for irrigation water. Due to the influence of the tectonic fault, the water supply of the ROI is mainly dependent on groundwater. Huge water demand has led to a continuous net deficit in aquifers, leading to land subsidence. The WAVS–InSAR strategy will be helpful for InSAR deformation monitoring at a national/regional scale and promoting the engineering application of InSAR technology.
... A unit vector in the north, east, and vertical directions has been used to represent the sensitivity of LOS measurement (Colesanti et al. 2003;Massonnet, Thatcher, and Vadon 1996). The method of deriving three-dimensional surface displacements from LOS displacements was originally applied to earthquake displacement field extraction (Fialko, Simons, and Agnew 2001;Hu et al. 2014;Wright 2004). In terms of the InSAR-related landslide measurement, Colesanti and Wasowski (2006) attempted to calculate the actual displacement along a westfacing slope from the LOS displacement. ...
Landslides are major geological hazards and frequently occur in mountainous areas with steep slopes, often causing significant loss. Interferometric Synthetic Aperture Radar (InSAR) has been widely used in landslide measurement over the last three decades. However, InSAR only can measure one-dimensional displacements (i.e. those in the radar’s line of sight (LOS) direction), resulting in the uncertainty between LOS displacement and the real slope displacement. In this paper, based on ascending and descending data from Sentinel-1 satellite, a wide-area potential landslide early identification was carried out using SBAS-InSAR in the whole of Mao County, a mountainous area in western Sichuan (China), with a total of 41 potential landslides successfully detected. Based on the quantitative analysis, the results show that the InSAR LOS measurement values are slope aspect and gradient-dependent. Finally, we innovatively derived a LOS displacement sensitivity map of InSAR in landslide measurement, revealing the relationship between LOS displacement, real displacements on slopes with arbitrary aspects and gradients, and SAR geometric distortion. This is a generalized finding useful for any slopes. It provides theoretical support to acquire and understand the real slope displacement from InSAR landslide measurement, which is vital to assist in correctly interpreting LOS displacement and carrying out subsequent quantitative geological engineering analysis. © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
... These point-based measurements are labour-intensive, time consuming and impractical for large-scale facilities (Gagliardi et al. 2021). Unlike these types of point-based measurements, Interferometric Synthetic Aperture Radar (InSAR) measurements provide large-scale measurements, with high spatial resolution in all weather conditions (Sun et al. 2021;Hu et al. 2014), which are comparable with these geodesic measurements and would substitute long-term settlement monitoring. ...
Istanbul Airport will be one of the biggest airports in the world when the construction in old open-pit mining areas which turned into wetlands is completed. To investigate the structural health monitoring of the Istanbul Airport, firstly the temporal evaluation of land use/land cover (LULC) in the region was generated for determining reclaimed lands using Random Forest classifier with Landsat images between 1984 and 2020. The outcomes were then examined with results of multi-temporal Interferometric Synthetic Aperture Radar (InSAR) methods, namely Small Baseline Subset (SBAS) for general displacement overview and Persistent Scatterer Interferometry (PSI) for detailed analysis of the settlement rate in the airport and runways which were applied to Sentinel-1 images. Both of the methods showed similar results for the same regionsand it is determined that there are movements up to 10 mm in Runway A and Runway B and more than 20 mm subsidence in Runway C.
... It relies on extracting the phase difference between complexvalued SAR images collected at separate times and from slightly different illumination angles [188][189][190]. Many advanced interferometric SAR methodologies [116,118,191,192] have been developed to process heterogeneous sets of SAR acquisitions collected from different orbiting SAR constellation sensors during the last two decades. These research techniques have greatly advanced from the investigation of single deformation events [193,194] to follow the time evolution of the ground deformations through multi-temporal differential InSAR (MT-InSAR) techniques [110][111][112][113]116,118,119,[195][196][197]. ...
Remote sensing technologies are extensively applied to prevent, monitor, and forecast hazardous risk conditions in the present-day global climate change era. This paper presents an overview of the current stage of remote sensing approaches employed to study coastal and delta river regions. The advantages and limitations of Earth Observation technology in characterizing the effects of climate variations on coastal environments are also presented. The role of the constellations of satellite sensors for Earth Observation, collecting helpful information on the Earth’s system and its temporal changes, is emphasized. For some key technologies, the principal characteristics of the processing chains adopted to obtain from the collected raw data added-value products are summarized. Emphasis is put on studying various disaster risks that affect coastal and megacity areas, where heterogeneous and interlinked hazard conditions can severely affect the population.
... In this context, traditional monitoring techniques, including leveling and GPS, provide high-accuracy surface deformation measurements but the obtained data are usually spatially discontinuous (Béjar-Pizarro et al. 2016;Hu et al. 2014). Therefore, for large-area subsidence monitoring, several serious obstacles are faced, including high monitoring costs, long survey periods, and complications involving monitored areas with complex terrain and difficult access points. ...
Landslides induced by mining always cause serious economic losses and human deaths in mining areas. The nature of these disasters argues for a reverse analysis of slope monitoring data to assess the cause, size, and temporal evolution and to further predict the potential risks of future disasters. In this paper, we investigated the Songmugou Landslide based on multisource remote sensing techniques. More specifically, we first investigated the geomorphological features and the time series subsidence rates across this slope from December 7, 2015 to April 26, 2019, by exploiting unmanned aerial vehicle (UAV) and small baseline subset interferometric synthetic aperture radar (SBAS-InSAR) monitoring, we then analyzed the deformation characteristics, active zonation, and secondary landslide risk of the study area by integrating geological, engineering, and rainfall data. Finally, we discussed reasonable evolution sequence and potential risk of the landslide and provided several suggestions for subsequent geological hazard prevention. The results indicate that this comprehensive approach can be used to back-analyze and reasonably predict the evolutionary mechanism of landslides.
... InSAR technology is an advanced geodetic tool that features fine spatial resolution, high measurement precision (in cm or less), and all-day and all-weather working capabilities. InSAR systems emit electromagnetic waves, collect and analyze the amplitude and phase of the returned energy from a target, usually used for retrieving complete 3D surface displacements [43,44]. Due to the promising performance of capturing the movement of active landslides, various InSAR techniques have been employed to detect potential slope failures [1,2,10,45], including the traditional InSAR [10], corner reflector InSAR [35], and squeeSAR technique [46]. ...
Landslides are among the most common geological hazards that result in considerable human and economic losses globally. Researchers have put great efforts into addressing the landslide prediction problem for decades. Previous methods either focus on analyzing the landslide inventory maps obtained from aerial photography and satellite images or propose machine learning models—trained on historical land deformation data—to predict future displacement and sedimentation. However, existing approaches generally fail to capture complex spatial deformations and their inter-dependencies in different areas. This work presents a novel landslide prediction model based on graph neural networks, which utilizes graph convolutions to aggregate spatial correlations among different monitored locations. Besides, we introduce a novel locally historical transformer network to capture dynamic spatio-temporal relations and predict the surface deformation. We conduct extensive experiments on real-world data and demonstrate that our model significantly outperforms state-of-the-art approaches in terms of prediction accuracy and model interpretations.
A precise finite‐fault model including the fault geometry and slip distribution is essential to understand the physics of an earthquake. However, the conventional linear inversion of geodetic data for a finite‐fault model cannot fully resolve the fault geometry. In this study, we developed a Bayesian inversion framework that can comprehensively solve a non‐planar fault geometry, the corresponding fault slip distribution with spatially variable directions, and objective weighting for multiple data types. In the proposed framework, the probability distributions of all the model parameters are sampled using the Monte Carlo method. The developed methodology removes the requirement for manual intervention for the fault geometry and data weighting and can provide an ensemble of plausible model parameters. The performance of the developed method is tested and demonstrated through inversions for synthetic oblique‐slip faulting models. The results show that the constant rake assumption can significantly bias the estimates of fault geometry and data weighting, whereas additional consideration of the variability of slip orientations can allow plausible estimates of a non‐planar fault geometry with objective data weighting. We applied the method to the 2013 Mw 6.5 Lushan earthquake in Sichuan province, China. The result reveals dominant thrust slips with left‐lateral components and a curved fault geometry, with the confidence interval of the dip angles being between 20°–25° and 56°–58°. The proposed method provides useful insights into the scope of imaging a non‐planar fault geometry, and could help to interpret more complex earthquake sources in the future.
Teknik Synthetic Aperture Radar (SAR) interferometri merupakan salah satu metode yang digunakan untuk pengamatan deformasi permukaan. Teknik SAR interferometri memiliki kelebihan yaitu dapat mengukur besarnya deformasi permukaan hingga satuan milimeter. Walaupun teknik SAR Interferometri memiliki kelebihan, teknik SAR interferometri tetap memiliki kekurangan yaitu hanya dapat memberikan informasi deformasi permukaan 1 dimensi (vertikal) saja. Kelemahan tersebut mengakibatkan teknik SAR interferometri sulit digunakan untuk membantu dalam proses interpretasi sumber dan mekanisme deformasi yang terjadi. Penelitian ini bertujuan untuk ekstraksi deformasi permukaan 2.5-D (2.5 Dimensi) akibat gempa bumi Iran 14 November 2021. Data yang digunakan untuk uji algoritma 2.5-D adalah citra SAR Sentinel-1 sebanyak 2 pasang citra. Citra tersebut adalah citra yang diakuisisi pada tanggal 13 November 2021 dan 19 November 2021. Citra SAR Sentinel-1A diolah menggunakan perangkat lunak GMTSAR dengan arah orbit ascending dan descending. Citra SAR Sentinel-1A yang sudah diolah menggunakan GMTSAR menghasilkan pergeseran permukaan tanah terhadap arah pandang satelit (Line of Sight). Hasil dari penelitian ini diketahui bahwa komponen horizontal terjadi pergeseran sebesar 200 mm ke arah barat. Pergeseran komponen vertikal mengalami kenaikan permukaan tanah sebesar 541 mm pada area utara dan penurunan permukaan tanah maksimal sebesar 231 mm pada area selatan. Berdasarkan hasil tersebut, diketahui bahwa nilai pergeseran komponen vertikal lebih besar daripada komponen horizontal. Hal tersebut menunjukkan bahwa gempa bumi Iran 14 November 2021 diindikasikan disebabkan oleh aktivitas sesar dengan mekanisme sesar naik (thrust fault).
With improvements in synthetic aperture radar (SAR) image resolutions and multitemporal SAR interferometry (MTInSAR) algorithms, it becomes feasible to generate 3D point clouds with millimeter deformation accuracy to monitor urban infrastructure health in detail. This article reviews the progress and challenges of MT interferometric SAR (InSAR) techniques for infrastructure deformation monitoring, with an emphasis on refinement performance. After a brief overview of literature statistics, we examine characteristics of the main MTInSAR algorithms. We demonstrate performance refinement in terms of point density, height accuracy, and deformation accuracy, using a comparative study of the reclaimed Hong Kong International Airport (HKIA). A series of typical infrastructure dynamic behaviors in urban areas revealed by MTInSAR is then illustrated. This article also describes key issues that remain to be addressed to facilitate operational fine surveillance. Finally, we go beyond MTInSAR to illustrate intelligent infrastructure diagnosis systems applicable to city-scale and even infrastructural component-scale analysis. It is our expectation that this review will provide a reference and guidance for future research and applications of MTInSAR in urban infrastructure monitoring.
Frequent rockfall events pose a major threat to the safe operation of the Taihang Grand Canyon Scenic Area (GCSA) in China. The traditional techniques for identifying potential rockfall sources and hazard assessment methods are often challenged in the alpine canyon landform. This study aims to establish an early identification framework for regional potential rockfall sources applicable to the canyon region and to assess rockfall hazards in potentially hazardous areas using unmanned aerial vehicle (UAV) photogrammetry. Specifically, by incorporating high-precision topographic information and geotechnical properties, the slope angle distribution method was used for static identification of potential rockfall sources. Moreover, SBAS-InSAR technology was used to describe the activity of potential rockfall sources. Finally, taking the key potentially hazardous area of the Sky City scenic spot as an example, the Rockfall Analyst tool was used to analyze the rockfall frequency, bounce height and energy characteristics based on the high-precision UAV 3D real scene model, and the analytic hierarchy process was introduced to achieve quantitative rockfall hazard assessment. The results show that the potential rockfall source areas in the Taihang GCSA is 33.47 km2 (21.47%), mainly distributed in strips on the cliffs on both sides of the canyon, of which the active rockfall source area is 2.96 km2 (8.84%). Taking the scenic spot of Sky City as example, the proposed UAV-based real scene modeling technology was proven to be able to quickly and accurately construct a 3D high-precision model of the canyon area. Moreover, the 3D rockfall simulation showed that the high-energy rockfall area was mainly distributed at the foot of the steep cliff, which mainly threatens the tourist distribution center below. The early identification and quantitative evaluation scheme of rockfall events proposed in this study can provide technical reference for the prevention and control of rockfall hazards in similar alpine valley areas.
Multitemporal synthetic aperture radar interferometry (MT-InSAR), capable of detecting both surface deformation and elevation with high precision, is used for many applications in earth observation. Conventional synthetic aperture radar (SAR) missions with a single beam only detect deformation along the line of sight (LOS) and relative elevation due to the undetermined model of phase wrapping. In a multisatellite SAR mission, measurements from different SAR geometry improve the sensitivity of the detectable deformation, especially to the deformation along the north–south (N-S) direction. However, it is difficult to combine the measurements from varying viewing angles since the absolute phase cannot be reconstructed without a ground control point. In this article, a tri-beam SAR system is introduced to detect 3-D deformation and derive multiview 3-D surface model from a single spaceborne platform. The accuracy of the 3-D deformation from the tri-beam SAR is exploited with varying squint and incident angles to obtain the optimal parameters of the three beams. Then a multidimensional coherent scattering model is used to simulate the multitemporal SAR data with different viewing angles. Regarding the tri-beam SAR, potential applications in earth observation including 3-D deformation monitoring, geodetic stereo SAR, and multiview 3-D forest reconstruction are investigated subsequently. The results of this study indicate that the tri-beam SAR is able to measure 3-D deformation and reconstruct 3-D surface model without ground control point.
The multi-level disturbance of underground and surface caused by coal mining activities intensifies the deterioration of the ecological environment in the mining area. Among them, the uneven settlement caused by coal mining is the most intuitive manifestation of surface environmental damage. The uneven settlement in the mining area has the characteristics of large settlement magnitude and severe deformation. Therefore, based on 15 Sentinel-1A image data, this paper uses three methods: SBAS InSAR, continuous D-InSAR and offset tracking technology to monitor the surface deformation of the mining area. The results show that the continuous D-InSAR technology SBAS-InSAR technology is applied to the small deformation in the edge area of the subsidence basin. The mining area with low gradient subsidence of SBAS-InSAR can obtain better performance than continuous D-InSAR technology. The offset tracking technique is used to monitor the large gradient deformation in the center of the subsidence basin. Therefore, this paper proposes to expand the quantitative analysis through the spatial coherence threshold and the accuracy and successful image elements of the interference fringe displacement. Combine the advantages of the three methods and overcome the shortcomings of each method, fuse the deformation information of the three methods, and obtain the deformation law of the whole surface subsidence. The results show that the mean absolute error (MAE1-1) of continuity D-InSAR is 0.92 m, the mean absolute error (MAE2-1) of SBAS-InSAR is 0.94 m, and the mean absolute error (MAE3-1) of Offset-tracking is 0.25 m. The results of this fusion method are in good agreement with the measured data, and the mean absolute error (MAE4-1) of vertical displacement is 7 cm. Therefore, the fusion method has advantages over individual methods and provides a new idea in monitoring the large gradient deformation of coal mining subsidence in mining areas.
Deniz dolgusuna veya ıslah edilen arazilere inşa
edilen havalimanları, gerek yapının ağırlığıyla zeminde
oturması ve gerekse de dolgu kili kullanıldığında kilin
zamanla şişmesi-kabarması sonucu yapıyı
kaldırmasına karşı oldukça hassas konumdadır. Ayrıca,
dolgularda zemin sıvılaşması tektonik hareketlere karşı
yapıyı daha da hassas bir hale getirmektedir. Zaman
içerisinde zeminde ve yapılarda meydana gelen
hareketlerin belirlenmesi amacıyla geliştirilen
Interferometrik Yapay Açıklıklı Radar (InSARInterferometric
Synthetic Aperture Radar) zaman serisi
yöntemleri, kullanılan uydu görüntülerinin mekânsal
çözünürlüğüne bağlı olarak mm mertebesinde meydana
gelen deformasyonları belirleyebilmektedir. Bu
çalışmada, sulak alanlar üzerine inşa edilen İstanbul
Havalimanı’nın kullanıma açıldığı Kasım 2018’den
Kasım 2021 yılına kadar meydana gelen yapısal
hareketler Sabit Saçıcı Interferometri (PSI-Persistent
Scatterer Interferometry) yöntemi kullanılarak
belirlenmiştir. Çalışmada, Avrupa Uzay Ajansı
tarafından ücretsiz olarak servis edilen ve yükselen
yörüngede alınan 186 Sentinel-1 SAR görüntüsü
kullanılmıştır. Ayrıca sonradan inşa edilen C pisti için
gerçekleştirilen analizde de Temmuz 2020-Kasım 2021
zaman aralığında 85 uydu görüntüsü kullanılmıştır. Elde
edilen sonuçlara göre havalimanının kuzey
kesimlerinde uydu bakış yönünde negatif yönde yüzey
hareketi tespit edilirken, güney kesimlerinde ise pozitif
yönde yüzey hareketi tespit edilmiştir. 73 ha sulak
alanın ıslah edildiği bölgenin çevresinde -20 mm’ye
varan yüzey hareketlerinin belirlenmesi,
havalimanlarında ıslah edilerek doldurulan alanların
zemin hareketlerine karşı daha hassas olduğunu
göstermektedir. Elde edilen sonuçlar, özellikle dolgu
alanlar üzerine inşa edilen yapılarda ve özellikle
havalimanlarında hem yersel hem de uydu bazlı sürekli
izleme sistemlerinin kurulması için yol gösterici olarak
kullanılabilecektir.
The Sichuan-Tibet traffic corridor is an important transportation strategy in China that plays a key role in the economic prosperity, long-term stability, and the "Belt and Road" strategy in western China. However, the complex terrain, climate environment and active geological tectonic movements along the Sichuan-Tibet traffic corridor lead to extremely developed geo-hazards, such as debris flows, landslides, glacial lake outbreak floods (GLOF), which have serious impacts on railway construction and operation. As a representative section, the Linzhi-Bomi is frequently affected by glacier debris flows, and deemed as the most difficult section for disaster mitigation. Although some conclusions about influencing factors and material properties of glacial debris flows have been achieved at the single-valley scale, there is lacking solid research on predisposing factors, evolution laws and catastrophe indicators of different types of glacial debris flows along the Sichuan-Tibet traffic corridor, making it impossible to build an effective monitoring and early warning system. In this paper, multi-source long-term remote sensing images and meteorological monitoring data, combined with field data, are applied to conduct an inductive analysis of the glacial debris flow along the Sichuan-Tibet traffic corridor. Four conclusions can be drawn. (1) 99 glacial debris flow valleys were identified in the study area, that mainly distributed in the Chaqing glacier-Yigong township, Jialabelei-Nangabawa peak, and Guxiang gully-Galongsi glacier. (2) Climate environment change has led to complex responses in glacier activities, characterised by increased activity of smaller glaciers (high-altitude hanging glaciers) and weakened activity of glaciers in large valleys in the past 40 years; (3) Based on the historic inventory, it can be found that the glacial debris flow has shown the characteristics of increasing frequency and scale since 1973. And (4) the frequency of the debris flows induced by landslides and ice-rock avalanches in steep terrain has increased. In the future, the continuous retreat of glaciers will promote the disappearance of ice waterfalls and the development of larger-scale hanging glaciers, which will increase the risk of glacial debris flows. The evolution process of glacial debris flows has obvious catastrophic indicators, such as: the increasing crevice density, the change in glacier velocities, and the rapid increase of glacial lake areas. Finally, it proposes a monitoring and early warning framework that contains satellites, aerial remote sensing platforms, meteorological and hydrological ground monitoring platforms, and ground motion monitoring platforms, which can provide catastrophic information for different types of glacial debris flows.
Interferometry and pixel offset tracking (POT) are two major technologies to measure ground deformation with repeat-pass synthetic aperture radar (SAR) observations. The SAR POT method can tolerate a much larger deformation gradient than interferometric SAR (InSAR), and thus it has been widely applied in monitoring earthquakes, volcanoes, landslides, glaciers, etc. However, there is an intrinsic trade-off between matching accuracy and detail preserving in terms of matching window size for the traditional SAR POT method using only single-polarization intensity. Taking advantage of polarimetric scattering properties, this study develops a novel POT method, named PCM-POT, towards mitigating the dependence of offset estimations on matching window size. It employs a generalized likelihood ratio test (GLRT) upon polarimetric covariance matrices (PCMs) to evaluate the similarity of two candidate pixels and estimate high-resolution surface displacements with high accuracy. The effectiveness and advantage of PCM-POT are demonstrated by an experiment of retrieving the displacements of the Slumgullion landslide from a pair of full-polarimetric UAVSAR images. Comparisons with the traditional POT indicate that using polarimetric scattering properties can reduce the uncertainty in offset estimations over heterogeneous sliding areas. Further experiments suggest that PCM-POT is also suitable for dual-polarimetric satellite SAR data.
The impoundment of reservoirs in canyons can aggravate the destruction of bank slopes. The Xingguang village landslide is located on the Xiluodu Reservoir in the lower reaches of the Jinsha River. It has deformed continuously since impoundment of the reservoir in 2012, and it seriously threatens the operational safety of the Xiluodu hydropower station. Its temporal and spatial deformation characteristics and its deformation mechanism have not been systematically monitored and explained. In this paper, the movement directions were identified based on the time-series cumulative displacement maps and the landslide is further partitioned into different sections by combining geomorphological data, stratigraphic occurrence, and lithological characteristics. The horizontal and vertical displacement characteristics of the two sections of the Xingguang village landslide were obtained by ascending and descending track interferometric synthetic aperture radar (InSAR) observation results and two-dimensional decomposition functions, and the results were further verified by a field survey and unmanned aerial vehicle (UAV) photography. The results show that the lithologic combination of alternating soft and hard anticline strata and the high steep bank slope cut by the Jinsha River are the internal factors responsible for the development of the Xingguang village landslide. The softening of the strata caused by water storage and the pressure difference caused by water level fluctuations reduce the slope stability. This study provides a new technical path to obtain the direction of landslide movement through time-series cumulative displacement maps and stratigraphic information and then identifies rock toppling in a remote way, which is of great significance for the prevention and control of rocky slope failures in canyon reservoir areas.
The deep-seated gravitational slope deformation (DSGSD) triggered by impoundment has attracted worldwide attention. After impoundment of Wudongde reservoir downstream of Jinsha River, China, Zaogutian DSGSD occurred with an estimated volume of 129 million m3, which provided an opportunity for in-depth analysis and cognition of its mechanism and risk. The DSGSD sits on a chair-shaped bedding bank slope with multi-weak interlayers at the bottom, forming a lithology structure of brittle cap overlying a ductile substratum. Based on the traditional engineering geological exploration, 3D observation of the DSGSD was carried out by UAV photogrammetry, and the cracks, discontinuities, and macroscopic deformation characteristics of different areas were identified. Combining the InSAR survey and surface-parallel flow assumption, the mm-level 3D deformation rate field and time-series displacement from December 2019 to December 2020 were reconstructed. Finally, the following conclusions were arrived at: according to the cracks and the boundary between rock mass and deposit, the DSGSD could be divided into four zones: the loose deposit near the bank, the scarp area in the front part, the major sliding area in the middle part, and the stable area. The loose deposits were deforming by uplifting with a maximum rate of 70 mm/year. The deformation rate in the western part of the major sliding area was the fastest, and the rates of the maximum settlement and southward deformation peaked at 100 mm/year and 250 mm/year, respectively, which were 2–3 times data in the scarp area. Under the soaking of reservoir water, the mechanical magnitude of the weak layer in the lower Dengying Formation and the Guanyinya Formation got reduced, which was the triggering factor of Zaogutian DSGSD. As a result, the major sliding area pushed the scrap area to creep along with the weak layer, and sliding accompanied by tensile fracturing is the instability mode in case of failure. The combination of InSAR and UAV observation provides a deeper insight into the deformation mechanism of DSGSD, which is not only conducive to slope stability evaluation but also demonstrates the role of remote sensing technology in the study of DSGSD.
Surface deformation monitoring plays a vital role in understanding landslide kinematics and slope failure analysis. In the past, applications of precise geodetic techniques have been successfully demonstrated for surface deformation analysis in natural hazard monitoring. This study presents, first of its kind in India, site-scale deformation analysis of a half-century old active landslide (Jaggi Bagwan) in Rudraprayag district, Uttarakhand state (India). We present an approach to investigate the spatial variability of surface deformation (i.e. sectors with different kinematics within a landslide) using multi-temporal interferometric Synthetic Aperture radar (MT-InSAR) derived strain map. The maximum negative mean displacement rates obtained by MT-InSAR processing of 30 Ascending and 32 descending Sentinel-1A scenes are 27.56 mm/yr and 1.11 mm/yr, respectively. It indicates the presence of instability at the study site which is further supported by a line of sight (LOS) projected Global Navigation Satellite System (GNSS) displacement rates. Subsequently, a modified least square method is applied to generate strain map using 3D velocity components obtained by multi-geometry LOS decomposition. The interpretation of strain map is further assisted by the instabilities observed at the crown of Jaggi Bagwan using Google Earth imageries from 1996 to 2018 to better correlate the strain pattern. Strain rate map clearly identified the sectors with dominating extension and compression within landslide. The presented approach can be further extended to landslide risk reduction along national highways and valley blockages.
Synthetic Aperture Radar Interferometry (InSAR) using satellite data is revealing a promising tool for monitoring long-term deformation phenomena in critical infrastructural systems. Nevertheless, its use in structural engineering is still quite limited and a general understanding of its potential is still missing, especially when dealing with bridge structures for which specific methods of data processing and displacement assessment with error quantification need to be developed, accounting for the type of deformation phenomena and for the orientation of the bridge. In order to partly fill this research gap, this paper proposes a post-processing methodology to derive two-dimensional displacement configurations of multi-span bridges with properly defined error bounds, using both ascending and descending Synthetic Aperture Radar acquisitions. In order to obtain an engineering meaningful estimate of the uncertainties affecting the reconstructed bridge deformations, both random and systematic errors are quantified, accounting for the orientation of the bridge with respect to the Line-Of-Sights of the satellites, the hypothesized deformation plane and the accuracy of InSAR measurements. The proposed procedure has been applied to the illustrative case study of the Albiano-Magra Bridge in Italy, collapsed on 8 April 2020. The results, referred to the monitoring period 2015–2020, demonstrate the effectiveness of the proposed method in supporting engineering assessments. In particular, an initially temperature-induced stationary deformation phenomenon has been observed, with all spans moving upwards or downwards during summer and winter. Afterwards, displacements of increasing amplitude for two side spans have been observed during the three years preceding the failure, providing information on the possible cause of collapse.
Differential Synthetic Aperture Radar Interferometry (DInSAR) can only measure one-dimensional deformation of surface along Radar line-of-sight (LOS). However, surface changes always exhibit three-dimensional (3D) characteristics. This paper presents a method to estimate 3D deformation of L'Aquila earthquake by combining multi-platform DInSAR LOS data based on the imaging geometry of Radar. The characters of the surface reflected by the 3D deformation are very consistent with the geological exploration. The 3D deformation was also compared with real GPS survey, and the results demonstrate that the 3D surface deformation fields are reliable and with high accuracy.
ERS – ENVISAT Tandem (EET) data are SAR data pairs acquired by the ERS-2 and ENVISAT ASAR instruments from approximately the same orbits within 28 minutes. During two dedicated campaigns in 2007/2008 and 2008/2009 ESA specifically acquired EET pairs with baselines suited for cross-interferometry (CInSAR). At perpendicular baselines of about 2km the frequency difference and baseline effects on the reflectivity spectrum compensate and so coherent interferograms can be obtained. Sea and shelf ice has usually a relatively flat surface and so there is little topographic phase observed, even for 2km perpendicular baselines. Centimeter scale motion occurring during the 28 minute interval results in deformation phase. Motion at this rate is often observed for sea and shelf ice and is of interest to understand dynamics and stress occurring. More open sea ice moves at even much higher rates. Here EET coherence is typically lost but offset tracking and split-beam interferometry may be used to retrieve motion fields. The sensitivities of these techniques are in the order of 1/20 of a SAR image pixel. So in azimuth direction this translates to a sensitivity of about 20cm per 28 minutes interval and in cross-track direction to about 1m per 28 minutes interval. On the other hand maximum rates which can reliably be retrieved correspond to offsets of several pixels between the two acquisitions corresponding to rates up to the order of 100m per 28 minutes interval. Repeat-pass interferometry, offset tracking, and split-beam interferometry were already applied in the past using data at different wavelengths and time intervals. So far the shortest interval available was 1 day from the ERS-1/2 Tandem mission. Now, EET data offers data at a much shorter 28 minutes interval. Consequently, faster motion rates can be investigated.
InSAR has the advantages of wide spatial coverage, high spatial resolution and high precision, but it can only measure one-dimensional surface displacements in line-of-sight (LOS). While GPS can monitor three-dimensional surface displacements, it is generally with very low spatial resolution. In this paper, the method of combining InSAR and GPS to measure three-dimensional surface displacements with high spatial resolution is studied. Firstly, it is proved that a local optimization method is sufficient to achieve the global optimization solutions of the objective function model, which is used to optimize the InSAR and GPS integration. Then the BFGS method is introduced in this study to estimate the optimal value of the three-dimensional surface displacement velocities. Compared to the global optimization method or the analytical optimization method, the BFGS method is very simple in computing and easy to converge, and has good resistance to numerical instability. In the last of the paper, the results of numerical simulations and real data experiments over Southern California are presented. They show a great improvement of accuracy when the proposed methods are used. Especially, when the observation or interpolation errors lead to ill-condition in the coefficient matrix of normal equations, the analytical optimization method can result in great errors, while the BFGS method works very well.
Glaciers are characterized by their flowability. Measurement of their velocity can provide important information for the study of glacier mass balance and glacier involved hazards. This paper applies seven ALOS/PALSAR images and the offset-tracking method to derive the displacement field of the largest mountain glacier in Asia, i. e., the South Inylchek Glacier. The temporal continuity of SAR images and the debris coverage of South Inylchek Glacier make the offset-tracking method successfully acquire continuous surface displacements. Several natural events such as snowfall in the firn basins, ablation of superimposed ice and development of crevasses in steep sections still have some influence on the results. However, the derived surface displacement maps of different periods are highly consistent with each other. The detail analysis reveals the following rules of the South Inylchek Glacier's motion: the velocity reduces from glacier axis to both sides, and increases from its origin to snowline and then reduces towards the end; the velocity is positively and nonlinearly correlated with the slope, especially when the slope increases sharply from 1 degrees to 16 degrees, the surge velocity will give rise to crevasses on the glacier; under the influence of glacial lake level changes, the velocity of tributary at the tail can surge to 96 cm/d; the summer velocity is 5 similar to 10 cm/d higher than winter one. Seen from all results, the normal velocity of the glacier trunk is between 20 and 50 cm/d, but can reach 65 cm/d in special place. The statistics of sampling points in the tongue indicates that mean velocity of different periods lies between 27.9 and 33.3 cm/d. Compared to the record in 2004, velocity derived in this research reduces about 5 cm/d.
Synthetic aperture radar (SAR) is a coherent active microwave imaging method. In remote sensing it is used for mapping the scattering properties of the Earth's surface in the respective wavelength domain. Many physical and geometric parameters of the imaged scene contribute to the grey value of a SAR image pixel. Scene inversion suffers from this high ambiguity and requires SAR data taken at different wavelength, polarization, time, incidence angle, etc. Interferometric SAR (InSAR) exploits the phase differences of at least two complex-valued SAR images acquired from different orbit positions and/or at different times. The information derived from these interferometric data sets can be used to measure several geophysical quantities, such as topography, deformations (volcanoes, earthquakes, ice fields), glacier flows, ocean currents, vegetation properties, etc. This paper reviews the technology and the signal theoretical aspects of InSAR. Emphasis is given to mathematical imaging models and the statistical properties of the involved quantities. Coherence is shown to be a useful concept for system description and for interferogram quality assessment. As a key step in InSAR signal processing two-dimensional phase unwrapping is discussed in detail. Several interferometric configurations are described and illustrated by real-world examples. A compilation of past, current and future InSAR systems concludes the paper.
The use of SAR interferometry is often impeded by decorrelation from thermal noise, temporal change, and baseline geometry. Power spectra of interferograms are typically the sum of a narrow-band component combined with broad-band noise. We describe a new adaptive filtering algorithm that dramatically lowers phase noise, improving both measurement accuracy and phase unwrapping, while demonstrating graceful degradation in regions of pure noise. The performance of the filter is demonstrated with SAR data from the ERS satellites over the Jakobshavns glacier of Greenland.
We recover the interseismic deformation along the entire San Andreas
Fault System (SAFS) at a spatial resolution of 200 meters by combining
InSAR and GPS observations using a dislocation model. Previous efforts
to compare 17 different GPS-derived strain rate models of the SAFS shows
that GPS data alone cannot uniquely resolve the rapid velocity gradients
near faults, which are critical for understanding the along-strike
variations in stress accumulation rate and associated earthquake hazard.
To improve the near-fault velocity resolution, we integrate new GPS
observations with InSAR observations, initially from ALOS (Advanced Land
Observation Satellite launched by Japan Aerospace Exploration Agency)
ascending data (spanning 2006.5-2010), using a remove/restore approach.
More than 1100 interferograms were processed with the newly developed
InSAR processing software GMTSAR. The integration uses a
dislocation-based velocity model to interpolate the Line-Of-Sight (LOS)
velocity at the full resolution of the InSAR data in radar coordinates.
The residual between the model and InSAR LOS velocity are stacked and
high-pass filtered, then added back to the model. This LOS velocity map
covers almost entire San Andreas Fault System (see Figure 1) from
Maacama Fault to the north to the Superstition Hills Fault to the south.
The average standard deviation of the LOS velocity model ranges from 2
to 4 mm/yr. Our initial results show previously unknown details in
along-strike variations in surface fault creep. Moreover, the high
resolution velocity field can resolve asperities in these "creeping"
sections that are important for understanding moment accumulation rates
and seismic hazards. We find that much of the high resolution velocity
signal is related to non-tectonic processes (e.g., ground subsidence and
uplift) sometimes very close to the fault zone. The near-fault
deformation signal extracted from this velocity map can provide tighter
constraints on fault slip rates and locking depths of the major fault
segments along the SAFS.
We compared four interseismic velocity models of the San Andreas Fault
based on GPS observations. The standard deviations of the predicted
secular velocity from the four models are larger north of the San
Francisco Bay area, near the creeping segment in Central California, and
along the San Jacinto Fault and the East California Shear Zone in
Southern California. A coherence spectrum analysis of the secular
velocity fields indicates relatively high correlation among the four
models at longer wavelengths (>15-40 km), with lower correlation at
shorter wavelengths. To improve the short-wavelength accuracy of the
interseismic velocity model, we integrated interferometric synthetic
aperture radar (InSAR) observations, initially from Advanced Land
Observing Satellite (ALOS) ascending data (spanning from the middle of
2006 to the end of 2010, totaling more than 1100 interferograms), with
GPS observations using a Sum/Remove/Filter/Restore approach. The final
InSAR line of sight data match the point GPS observations with a mean
absolute deviation of 1.5 mm/yr. We systematically evaluated the fault
creep rates along major faults of the San Andreas Fault and compared
them with creepmeters and alignment array data compiled in Uniform
California Earthquake Rupture Forecast, Version 2 (UCERF2). Moreover,
this InSAR line of sight dataset can constrain rapid velocity gradients
near the faults, which are critical for understanding the along-strike
variations in stress accumulation rate and associated earthquake hazard.
The propagation delay when radar signals travel from the troposphere has
been one of the major limitations for the applications of high precision
repeat-pass Interferometric Synthetic Aperture Radar (InSAR). In this
paper, we first present an elevation-dependent atmospheric correction
model for Advanced Synthetic Aperture Radar (ASAR - the instrument
aboard the ENVISAT satellite) interferograms with Medium Resolution
Imaging Spectrometer (MERIS) integrated water vapour (IWV) data. Then,
using four ASAR interferometric pairs over Southern California as
examples, we conduct the atmospheric correction experiments with
cloud-free MERIS IWV data. The results show that after the correction
the rms differences between InSAR and GPS have reduced by 69.6 per cent,
29 per cent, 31.8 per cent and 23.3 per cent, respectively for the four
selected interferograms, with an average improvement of 38.4 per cent.
Most importantly, after the correction, six distinct deformation areas
have been identified, that is, Long Beach-Santa Ana Basin,
Pomona-Ontario, San Bernardino and Elsinore basin, with the deformation
velocities along the radar line-of-sight (LOS) direction ranging from
-20 mm yr-1 to -30 mm yr-1 and on average around
-25 mm yr-1, and Santa Fe Springs and Wilmington, with a
slightly low deformation rate of about -10 mm yr-1 along LOS.
Finally, through the method of stacking, we generate a mean deformation
velocity map of Los Angeles over a period of 5 yr. The deformation is
quite consistent with the historical deformation of the area. Thus,
using the cloud-free MERIS IWV data correcting synchronized ASAR
interferograms can significantly reduce the atmospheric effects in the
interferograms and further better capture the ground deformation and
other geophysical signals.
Differential synthetic aperture radar interferometry (D-InSAR) can only measure one-dimensional surface displacements along the line-of-sight (LOS) direction which greatly inhibits its development and application. In this paper, we introduce a novel approach to measuring two-dimensional (2-D) surface displacements by exploiting a single InSAR pair, which is called multi-aperture InSAR (MAI) technology. We study the effects of baseline errors and the ionosphere on MAI technology and develop a directional filter and interpolator to minimize the ionospheric effects. A PALSAR image pair covering the 2010 Yushu earthquake is used to estimate the 2-D displacement fields of the earthquake using the MAI approach. The experimental results show that MAI is superior to conventional Offset-Tracking and therefore has great potential in co-seismic displacement measurement and source parameter inversion.
Differential interferometric synthetic aperture radar (D-InSAR) measures ground deformation only along the line-of-sight (LOS) of the radar, which limits the capability of D-InSAR in investigating the surface damages and the focus mechanisms of earthquakes. We do a three-dimensional (3D) decomposition of the coseismic displacement of the Darfield, New Zealand earthquake that occurred on 3 September 2010 by exploiting the Multi-Aperture InSAR (MAI) and D-InSAR measurements from both ascending and descending L-band PALSAR data. Due to the dispersive nature of the ionosphere and the slight Doppler shift between the forward- and backward-looking interferograms, the ionospheric effects can be more serious in MAI measurements than in D-InSAR. We propose mitigating the ionospheric effects in the MAI processing with the directional filtering and interpolation procedure that has been applied in Offset-tracking. The rupture revealed by the 3D surface displacement fits closely to the Greendale fault, which is believed to be responsible for the earthquake. The horizontal ground motions, mostly eastwards in the hanging wall and westwards in the footwall, reached up to 2.5 m and are anti-symmetric with respect to the Greendale fault. Up to 2.5 m subsidence occurred in the hanging wall, while uplift is found in the footwall with an extreme case of 1.6 m in the far left of the fault. This makes us conclude that the Greendale fault is a normal and dextral strike-slip. It is seen that the MAI measurements are very helpful in the derivation of 3D coseismic displacement fields as it provides more accurate displacement estimation in the north–south direction.
This paper describes the fundamental scientific and observational goals of the Southern California Integrated GPS Network (SCIGN). It also reviews the organizational structure, the project management, and important policies. Recent accomplishments are also discussed in some detail, in particular the effective response following the October 16, 1999 Hector Mine earthquake (Mw7.1). The scientific motivation for establishing a continuous GPS network to observe time transient crustal deformation is discussed in detail, especially as it pertains to the 1990's sequence of fault interaction and postseismic deformation in the eastern California shear zone. As of March 2001, a total of 239 SCIGN stations are operating; 170 of the newest stations were installed by a contractor. The third phase of network construction was recently completed at an average rate of 2 new stations per week. Network implementation is continuing, and construction of the final 16 stations will be fully completed by July 1, 2001.
While conventional interferometric synthetic aperture radar (InSAR) is a very effective technique for measuring crustal deformation, almost any interferogram includes large areas where the signals decorrelate and no measurement is possible. Persistent scatterer (PS) InSAR overcomes the decorrelation problem by identifying resolution elements whose echo is dominated by a single scatterer in a series of interferograms. Existing PS methods have been very successful in analysis of urban areas, where stable angular structures produce efficient reflectors that dominate background scattering. However, man-made structures are absent from most of the Earth's surface. Furthermore, existing methods identify PS pixels based on the similarity of their phase history to an assumed model for how deformation varies with time, whereas characterizing the temporal pattern of deformation is commonly one of the aims of any deformation study. We describe here a method for PS analysis, StaMPS, that uses spatial correlation of interferogram phase to find pixels with low-phase variance in all terrains, with or without buildings. Prior knowledge of temporal variations in the deformation rate is not required for their identification. We apply StaMPS to Volcán Alcedo, where conventional InSAR fails because of dense vegetation on the upper volcano flanks that causes most pixels to decorrelate with time. We detect two sources of deformation. The first we model as a contracting pipe-like body, which we interpret to be a crystallizing magma chamber. The second is downward and lateral motion on the inner slopes of the caldera, which we interpret as landsliding.
Land subsidence in Las Vegas, Nevada, United States, between April 1992 and December 1997 was measured using spaceborne interferometric synthetic aperture radar. The detailed deformation maps clearly show that the spatial extent of subsidence is controlled by geologic structures (faults) and sediment composition (clay thickness). The maximum detected subsidence during the 5.75 yr period is 19 cm. Comparison with leveling data indicates that the subsidence rates declined during the past decade as a result of rising ground-water levels brought about by a net reduction in ground-water extraction. Temporal analysis also detects seasonal subsidence and uplift patterns, which provide information about the elastic and inelastic properties of the aquifer system and their spatial variability.
Datong is located in the north of Shanxi Province, which is famous for its old-fashioned coal-mining preservation in China. Some serious issues such as land subsidence, ground fissures, mining collapse, and earthquake hazards have occurred over this area for a long time resulting in significant damages to buildings and roads.In order to monitor and mitigate these natural man-made hazards, Short Baseline Subsets (SBAS) InSAR technique with ten Envisat ASAR data is applied to detect the surface deformation over an area of thousands of square kilometers. Then, five MODIS data are used to check the atmospheric effects on InSAR interferograms. Finally, nine nonlinear land subsidence cumulative results during September 2004 and February 2008 are obtained.Based on the deformation data, three kinds of land subsidence are clearly detected, caused by mine extraction, underground water withdrawal and construction of new economic zones, respectively. The annual mean velocity of subsidence can reach 1 to 4cm/year in different subsidence areas. A newly designed high-speed railway (HSR) with speeds of 350km/h will cross through the Datong hi-tech zone. Special measures should be taken for the long run of this project. In addition, another two subsidence regions need further investigation to mitigate such hazards.
Multiple SAR interferograms are used to solve for the full 3-dimensional displacement of the surface of the Henrietta Nesmith Glacier in northern Ellesmere Island Canada. The approach exploits the incidence angle flexibility of different ascending and descending beam modes, and the azimuth angle diversity which occurs when different incidence angles are used at high latitudes. Line-of-sight displacements are estimated in 3 different orientations from the terrain corrected unwrapped differential phase and used to solve for the displacements in a local East, North, Up frame. Uncertainty in the absolute line-of-sight displacements limits the absolute accuracy for vertical displacement, however the relative solution coupled with knowledge of the surface slope allows spaceborne mapping of relative glacier thickening or thinning with unprecedented spatial resolution and with an accuracy of order a millimeter per day.
Despite remarkable successes achieved by Differential InSAR, estimations of low tectonic strain rates remain challenging in areas where deformation and topography are correlated, mainly because of the topography-related atmospheric phase screen (APS). In areas of high relief, empirical removal of the stratified component of the APS may lead to biased estimations of tectonic deformation rates. Here we describe a method to correct interferograms from the effects of the spatial and temporal variations in tropospheric stratification by computing tropospheric delay maps coincident with SAR acquisitions using the ERA-Interim global meteorological model. The modeled phase delay is integrated along vertical profiles at the ERA-I grid nodes and interpolated at the spatial sampling of the interferograms above the elevation of each image pixel. This approach is validated on unwrapped interferograms. We show that the removal of the atmospheric signal before phase unwrapping reduces the risk of unwrapping errors in areas of rough topography.
We use Interferometric Synthetic Aperture Radar (InSAR) data to derive continuous maps for three orthogonal components of the co-seismic surface displacement field due to the 1999 Mw7.1 Hector Mine earthquake in southern California. Vertical and horizontal displacements are both predominantly antisymmetric with respect to the fault plane, consistent with predictions of linear elastic models of deformation for a strike-slip fault. Some deviations from symmetry apparent in the surface displacement data may result from complexity in the fault geometry.
Data from interferometric synthetic aperture radar (INSAR) can provide three-dimensional information by using the phase as an additional information source derived from the complex radar data. In this paper, the issues, techniques and applications of SAR interferometry are reviewed. After a brief historical review, the geometric implementations of SAR interferometry are described. The general processing techniques are summarized and an introduction to various phase unwrapping techniques is given. Besides the differential use of SAR interferometry, the review focuses on parameters such as baseline, decorrelation and motion compensation which have a limiting influence on the quality of the data. After evaluating the various existing and potential applications using SAR interferometric techniques such as topographic mapping, digital elevation modelling, slope measurement, change detection, classification, ocean currents, polar research, seismic events and volcanic hazards, the paper concludes with some research issues, trends and developments in SAR interferometry. The paper is illustrated by examples of SAR interferometric data and derived products from the ESA ERS-1/ERS-2 and SIR-C/X-SAR satellite mission and from single pass aircraft data. An extensive list of references and bibliography on SAR interferometry is provided at the end of this review paper.
Fusion of synthetic aperture radar (SAR) images through interferometric, polarimetric and tomographic processing provides an all-weather imaging capability to characterise and monitor various natural hazards. This article outlines interferometric synthetic aperture radar (InSAR) processing and products and their utility for natural hazards characterisation, provides an overview of the techniques and applications related to fusion of SAR/InSAR images with optical and other images and highlights the emerging SAR fusion technologies. In addition to providing precise land-surface digital elevation maps, SAR-derived imaging products can map millimetre-scale elevation changes driven by volcanic, seismic and hydrogeologic processes, by landslides and wildfires and other natural hazards. With products derived from the fusion of SAR and other images, scientists can monitor the progress of flooding, estimate water storage changes in wetlands for improved hydrological modelling predictions and assessments of future flood impacts and map vegetation structure on a global scale and monitor its changes due to such processes as fire, volcanic eruption and deforestation. With the availability of SAR images in near real-time from multiple satellites in the near future, the fusion of SAR images with other images and data is playing an increasingly important role in understanding and forecasting natural hazards.
ERS SAR amplitude images are utilized to map ground displacements from a sub-pixel correlation method. It yields a ground two-dimensional displacement field with independent measurements about every 128m in azimuth and 250m in range. The accuracy depends on the characteristics of the images. For the Landers test case, the 1-sigma uncertainty is 0.8m in range and 0.4m in azimuth. We show that this measurement provides a map of major surface fault ruptures accurate to better than 1km and information on coseismic deformation comparable to the 92 GPS measurements available. Although less accurate, this technique is more robust than SAR interferometry and provides complementary information since interferograms are only sensitive to the displacement in range.
The movements produced by the 1992 earthquake in Landers, California are mapped using SAR interferometry. An interferogram is constructed by combining topographic information with SAR images obtained by the ERS-1 satellite before and after the earthquake. It is shown that the observed changes in the range from the ground surface to the satellite agree well with the slip measured in the field, with the displacements measured by surveying, and with the results of Okada's (1985) elastic dislocation model. This interferogram provides a denser spatial sampling than surveying methods and a better precision than earlier space imaging techniques.
We use Envisat Advanced Synthetic Aperture Radar data and SPOT optical imagery to investigate the coseismic and postseismic deformation due to the 27 September 2003, M w 7.2 Altai earthquake, which occurred in the Chuya Basin near the Russia-China-Mongolia border. On the basis of the synthetic aperture radar (SAR) and SPOT data, we determined the rupture location and developed a coseismic slip model for the Altai earthquake. The inferred rupture location is in a good agreement with field observations, and the geodetic moment from our slip model is consistent with the seismic moment determined from the teleseismic data. While the epicentral area of the Altai earthquake is not optimal for radar interferometry (in particular, due to temporal decorrelation), we were able to detect a transient signal over a time period of 3 years following the earthquake. The signal is robust in that it allows us to discriminate among several commonly assumed mechanisms of postseismic relaxation. We find that the postearthquake interferometric SAR data do not warrant poroelastic rebound in the upper crust. The observed deformation also disagrees with linear viscoelastic relaxation in the upper mantle or lower crust, giving rise to a lower bound on the dynamic viscosity of the lower crust of the order of 1019 Pa s. The data can be explained in terms of fault slip within the seismogenic zone, on the periphery of areas with high coseismic slip. Most of the postseismic deformation can be explained in terms of seismic moment release in aftershocks; some shallow slip may have also occurred aseismically. Therefore the observed postseismic deformation due to the Altai earthquake is qualitatively different from deformation due to other similarly sized earthquakes, in particular, the Landers and Hector Mine earthquakes in the Mojave desert, southern California. The observed variations in the deformation pattern may be indicative of different rheologic structure of the continental lithosphere in different tectonically active areas.