Interferometric Synthetic Aperture Radar Images Research Articles

A Simple and Sustainable Prediction Method of Liquefaction-Induced Settlement at Pohang Using an Artificial Neural Network

Conventionally, liquefaction-induced settlements have been predicted through numerical or analytical methods. In this study, a machine learning approach for predicting the liquefaction-induced settlement at Pohang was investigated. In particular, we examined the potential of an artificial neural network (ANN) algorithm to predict the earthquake-induced settlement at Pohang on the basis of standard penetration test (SPT) data. The performance of two ANN models for settlement prediction was studied and compared in terms of the R2 correlation. Model 1 (input parameters: unit weight, corrected SPT blow count, and cyclic stress ratio (CSR)) showed higher prediction accuracy than model 2 (input parameters: depth of the soil layer, corrected SPT blow count, and the CSR), and the difference in the R2 correlation between the models was about 0.12. Subsequently, an optimal ANN model was used to develop a simple predictive model equation, which was implemented using a matrix formulation. Finally, the liquefaction-induced settlement chart based on the predictive model equation was proposed, and the applicability of the chart was verified by comparing it with the interferometric synthetic aperture radar (InSAR) image.

High‐quality interferometric inverse synthetic aperture radar imaging using deep convolutional networks

AbstractIn this article, a modified complex‐valued convolutional neural network (MCV‐CNN) specifically for interferometric inverse synthetic aperture radar (InISAR) imaging is proposed. Comparing with the fast Fourier transformation‐based and sparsity‐driven imaging algorithms, the MCV‐CNN can achieve super‐resolution and side‐lobe suppression on the imaging results simultaneously within a short time. The inputs of the MCV‐CNN are complex‐valued radar echo data, and the outputs are complex‐valued ISAR images which contain both the amplitude and phase information. Then the phase information is adopted to perform an interferometric operation, and the high‐quality three‐dimensional InISAR imaging results can be achieved. A 0.22 THz InISAR imaging experiment has been carried out to show the superiority of the proposed method on imaging quality and computational efficiency.

Bi-static high resolution imaging for ship targets with sparse apertures and its application in InISAR

ABSTRACTIn this letter, we focus on the high-resolution imaging of ship targets under sparse aperture condition and its application in three-dimensional (3D) imaging. A bi-static high-resolution algorithm dealing with the sparse echo condition is proposed, which consists of the following processing steps: (1) A side-lobe apodization–multiple orthogonal least-square method is proposed to recover the complete signal and reduce the influence of side-lobe at the same time, which enhances the precision of phase extraction in interferometric inverse synthetic aperture radar (InISAR) imaging; (2) The bi-static configuration is used to accentuate the relative motion between the target and radar, such that the requirement for long coherence processing time can be avoided and (3) The 3D InISAR technique is employed to obtain the 3D images of the ship targets. Experiments with simulated and real data are utilized to demonstrate the effectiveness of the proposed method.

Forecasting the magnitude of potential landslides based on InSAR techniques

A new method, combining empirical modeling with time series Interferometric Synthetic Aperture Radar (InSAR) data, is proposed to provide an assessment of potential landslide volume and area. The method was developed to evaluate potential landslides in the Heitai river terrace of the Yellow River in central Gansu Province, China. The elevated terrace has a substantial loess cover and along the terrace edges many landslides have been triggered by gradually rising groundwater levels following continuous irrigation since 1968. These landslides can have significant impact on communities, affecting lives and livelihoods. Developing effective landslide risk management requires better understanding of potential landslide magnitude. Fifty mapped landslides were used to construct an empirical power-law relationship linking landslide area (AL) to volume (VL) (VL = 0.333 × AL1.399). InSAR-derived ground displacement ranges from −64 mm/y to 24 mm/y along line of sight (LOS). Further interpretation of patterns based on remote sensing (InSAR & optical image) and field survey enabled the identification of an additional 54 potential landslides (1.9 × 102 m2 ≤ AL ≤ 8.1 × 104 m2). In turn this enabled construction of a map that shows the magnitude of potential landslide activity. This research provides significant further scientific insights to inform landslide hazard and risk management, in a context of ongoing landscape evolution. It also provides further evidence that this methodology can be used to quantify the magnitude of potential landslides and thus contribute essential information towards landslide risk management.

The 2019 Mw 6.4 and Mw 7.1 Ridgecrest earthquake sequence in Eastern California: rupture on a conjugate fault structure revealed by GPS and InSAR measurements

SUMMARYOn 4 and 6 July 2019, an Mw 6.4 foreshock and an Mw 7.1 main shock successively struck the city of Ridgecrest in eastern California. These two events are the most significant earthquake sequences to strike in this part of California for the past 20 yr. We used both continuous global positioning system (GPS) measurements and interferometric synthetic aperture radar (InSAR) images taken by the Sentinel-1 and ALOS-2 satellites in four different viewing geometries to fully map the coseismic surface displacements associated with these two earthquakes. Using these GPS and InSAR measurements both separately and jointly, we inverted data to find the coseismic slip distributions and fault dips caused by the two earthquakes. The GPS-constrained slip models indicate that the Mw 7.1 main shock was predominately controlled by right-lateral motions on a series of northwest-trending faults, while the Mw 6.4 foreshock involved both right-lateral slipping on a northwest-trending fault and left-lateral slipping on a northeast-trending fault. The two earthquakes both generate significant surface slip, with the maximum inferred slip of 5.54 m at the surface. We estimate the cumulative geodetic moment of the two earthquakes to have been 4.93 × 1019 Nm, equivalent to Mw 7.1. Furthermore, our calculations of the changes in static Coulomb stress suggest that the Mw 7.1 main shock was promoted significantly by the Mw 6.4 foreshock. This latest Ridgecrest earthquake sequence ruptured only the northern part of the seismic gap between the 1992 Mw 7.3 Landers earthquake and the 1872 M 7.4–7.9 Owens Valley earthquake. The earthquake risk in this area, therefore, remains very high, considering the significant accumulation of strain in the Eastern California Shear Zone, especially in the southern part of the seismic gap.

STUDY ON ACCURACY ASSESSMENT OF DEM IN THE MARSH USING WITH INTERFEROMETRIC PALSAR, SENTINEL-1A AND TERRASAR-X IMAGES

Abstract. To conserve and manage wetland resources, it is important to monitor hydro-geomorphic condition. In this paper, the interferometric SAR images of L-band ALOS-1 PALSAR, C-band Sentinel-1A and X-band TerraSAR were selected to produce DEM of wetland area in the Honghe National Nature Reserve using the InSAR technique. 111 testing points randomly selected from the 1:10000 topographic map were utilized to evaluate accuracy of remote-sensing based DEM. Finally, the interference coherence difference of wetland vegetation among three different wavelengths was compared and analyzed. The results showed that The DEM of wetland area produced by L-band ALOS-1 PALSAR interferometric images was in good agreement with the 1:10,000 topographic map data. The elevation value with the difference less than 3 meters account for over 76% of all testing points. The coherence coefficient of wetland calculated from PALSAR images was higher than Sentinel-1A and TerraSAR images. The coherence coefficient among wetland vegetation types was significantly different. The distribution area of forest and shrub-grass vegetation had a larger coherence coefficient than shallow-water marsh vegetation area and deep-water marsh vegetation area.

Backscatter Distributions of Persistent and Distributed Scatterers Over Wavelength: Results From X-, C-, and L-Band

Persistent scatterer (PS) techniques are a set of important time-series tools for interferometric synthetic aperture radar (InSAR) that enable deformation analysis in highly decorrelated terrain. Detailed knowledge of the statistics of persistent scatterers in InSAR images is critical for the design of better techniques that will enable both the extraction of deformation in traditionally difficult regions as well as develop a better understanding of how performance of these algorithms relates to important system parameters. In this article, we characterize the backscatter statistics of both persistent and distributed scatterers over wavelength using data from X -band (COSMO-SkyMed), C -band (Sentinel-1), and L -band (ALOS) sensors. We show that popular distributions that have previously been used to fit SAR backscatter can effectively capture the returns from both PS and clutter, with the $\text {G}^0$ distribution being the most applicable across wavelength and scatterer type. Thus, our work paves the way for improved detection algorithms to be designed based on these distributions and also builds an initial foundation for developing a greater theoretical understanding of PS statistics.

Coseismic Rupture Geometry and Slip Rupture Process During the 2018 Mw 7.1 Anchorage, South‐Central Alaska Earthquake: Intraplate Normal Faulting by Slab Tear Constrained by Geodetic and Teleseismic Data

AbstractThe Mw 7.1 Anchorage earthquake on 30 November 2018 beneath the south‐central Alaska is a rare intermediate‐depth event larger than Mw 7 that occurred in a complex subduction region, where the young Yakutat oceanic terrane wedges in the continental‐oceanic plate collisional region between the Pacific oceanic plate and the North American plate. We use both ascending and descending Sentinel‐1 satellite Interferometric Synthetic Aperture Radar (InSAR) images to construct the coseismic displacement associated with this earthquake, which shows a nearly circular deformation pattern with a subsidence of ~4 cm in line of sight direction. Combining coseismic GPS data, we determine the focal mechanism of this event dominated by normal faulting with N‐S striking of 186°and westward dipping of 64°by using a uniform slip model. Then we find a preferred slip model with both geodetic data and teleseismic data, suggesting the main slips are concentrated on a depth of 55–75 km. The total released moment of our preferred slip model is 5.32 × 1019N·m, equivalent to Mw 7.1. The rupture process includes two peaks terminating at about 18 s and indicates a unilateral rupture with its front propagating northwestward direction at an average speed of 2.5 km/s. In comparison with the detailed seismic image in this region, this event just occurred in the Yakutat terrane beneath a low velocity zone, suggesting it was caused by slab tear but not slab boundary breaking and determining the lower boundary of shallow thrust‐slip in the Alaska subduction zone.

Application of DInSAR for short period monitoring of initial subsidence due to longwall mining in the mountain west United States

Differential Interferometric Synthetic Aperture Radar (DInSAR), a satellite-based remote sensing technique, has application for monitoring subsidence with high resolution over short periods. DInSAR uses radar images to measure centimeter-level surface displacements. In the images, ground resolution can be relatively high, with each data point (pixel) representing the average displacement over an area of several square meters. The image data are acquired regularly which allows subsidence to be monitored sequentially over short periods; imaging periods typically range from weeks to months. Monitoring subsidence over short periods with high spatial resolution has potential to provide insight into the dynamics of subsidence and into relationships between mine advance and subsidence. In this study, for three longwall mines in the western United States, initial subsidence occurring at the start of longwall advance is quantified over short periods (12–72 days). C-band interferometric wide swath Synthetic Aperture Radar (SAR) images from the Sentinel satellites are used to quantify the subsidence. Overall, the data show initial development of subsidence, expansion of the subsidence trough, and the advance of subsidence in the direction of mining.

Unsupervised classification using polarimetric interferometric decomposition and Wishart classifier

ABSTRACTIn this paper, a decomposition scheme of the coherency matrix is presented to parse the information of polarimetric interferometric synthetic aperture radar (PolInSAR) images in detail. First, the decomposition method is improved by the polarimetric interferometric similarity parameter (PISP) to relief the overestimation occurred in the traditional four-component decomposition method. Second, after using the improved four-component decomposition results as the original inputs, the decomposition method is applied to retrieve scattering mechanisms or identify scatters, with the image separated into seven subsections. Finally, based on the modified decomposition results, the basic classification results are regarded as the feature training sets, and the Wishart classifier is then used as an optimized classification process. The applications of the decomposition and classification scheme are shown with typical representative L-band E-SAR images, which are used to show the robustness of the method, as well as with the first published airborne C-band PolInSAR data collected by the Institute of Electronics, Chinese Academy of Sciences, in November 2017. Experimental results demonstrate that the obtained decomposition and classification results are in good agreement with the actual physical scattering mechanisms.

Surface Faulting and Ground Deformation: Considerations on Their Lower Detectable Limit and on FDHA for Nuclear Installations

We performed a review of a representative data set on coseismic surface deformation, derived from both interferometric synthetic aperture radar imaging and from a traditional field survey of surface faulting. This analysis indicates a minimum threshold value of M w 5.4–5.5 for earthquake-induced ground deformation and faulting, with an inherently lower limit of detection that makes it hard to recognize surface deformation caused by M w < 4.5–5.0 events. Significant exceptions are represented by shallow (i.e., less than circa 5 km) events that occur in volcano-tectonic settings, where surface deformation and dislocation are also clearly detectable for M w circa 4.0. Furthermore, a statistically significant regression between the areal extent of surface deformation and maximum slip at surface is proposed. This correlation is discussed in relation to fault displacement hazard analysis for nuclear power plants. In particular, the deformation area is used to find a potential solution for the second and third criterion for defining a capable fault.

Deformation associated with sliver transport in Costa Rica: seismic and geodetic observations of the July 2016 Bijagua earthquake sequence

SUMMARYTectonic slivers form in the overriding plate in regions of oblique subduction. The inner boundaries of the sliver are often poorly defined and can consist of well-defined faults, rotating blocks or diffuse fault systems, which pass through or near the volcanic arc. The Guanacaste Volcanic Arc Sliver (GVAS) as defined by Montero et al., is a segment of the Central American Forearc Sliver, whose inner boundary is the ∼87-km-long Haciendas-Chiripa fault system (HCFS), which is located ∼10 km behind the volcanic arc and consists of strike slip faults and pull apart steps. We characterize the current ground motion on this boundary by combining earthquake locations and focal mechanisms of the 2016 Bijagua earthquake sequence, with the surface ground deformation obtained from Interferometric Synthetic Aperture Radar (InSAR) images from the ALOS-2 satellite. The coseismic stack of interferograms show ∼6 cm of displacement towards the line of sight of the satellite between the Caño Negro fault and the Upala fault, indicating uplift or SE horizontal surface displacement. The largest recorded earthquake of the sequence was Mw 5.4, and the observed deformation is one of the smallest earthquakes yet detected by InSAR in the Central American region. Forward and inverse models show the surface deformation can be partially explained by slip on a single fault, but it can be better explained by slip along two faults linked at depth. The best-fitting model consists of 0.33 m of right lateral slip on the Caño Negro fault and 0.35 m of reverse slip on the Upala fault, forming a positive flower structure. As no reverse seismicity was recorded, we infer the slip on the Upala fault occurred aseismically. Observations of the Bijagua earthquake sequence suggests the forearc sliver boundary is a complex and diffuse fault system. There are localized zones of transpression and transtension and areas where there is no surface expression suggesting the fault system is not yet mature. Although aseismic slip is common on subduction interfaces and mature strike-slip faults, this is the first study to document aseismic slip on a continental tectonic sliver boundary fault.

Ship wake region detection by using multi‐feature recombination and area‐based morphological analysis in ATI‐SAR systems

For moving ship detection in synthetic aperture radar (SAR) images, ship wakes on the sea surface may be detectable, thus leading to interferences in reconnaissance. To address this issue, a wake region detection approach by using multi-feature recombination and area-based morphological analysis is proposed with along-track interferogram-SAR systems. This approach aims to detect the near-ship wake region that is nearby a ship's hull and between two kelvin cusp lines. A novel test is constructed by recombining magnitude, phase, and the local variance of phase in the complex multi-look interferometric SAR image to detect the potential pixels of the ship wakes. Then, with a clustering algorithm based on the proposed test and the pixel spatial distance, the potential wake regions are acquired, and the real ones having sufficiently large areas can be accurately determined. Finally, experimental results on the TerraSAR-X dataset validate the effectiveness of the proposed method.

Imaging of Bunkers Under Slightly Rough Terrain With Clutter-Suppressed, Subsurface Interferometric SAR

A subsurface interferometric synthetic aperture radar imaging technique is proposed for the detection and localization of clandestine underground facilities in the presence of a rough ground surface. The new approach consists of a two-step procedure: first, exploiting the distinctive scattering behaviors of the ground surface and the target, clutter suppression is performed with a polarimetric difference operation that does not alter the propagation phase of the target scattered signal, and then, a subsurface interferometric algorithm is applied to infer target depth by correlating the clutter-suppressed images obtained at two observation angles. The performance of the overall sensing algorithm for scene depth profile mapping from an airborne system is demonstrated with full-wave simulation data.

Discontinuity preserving phase unwrapping algorithm for simulated InSAR based on MRF model using line process

Phase unwrapping (PU) is one of the important procedures in measuring digital elevation model (DEM) from interferometric synthetic aperture radar (InSAR) images. It is known that the existence of phase discontinuity poses challenges to the traditional PU algorithms. In this study, the authors propose a coupled Markov random fields (MRF) called line process (LP) for PU, abbreviated as the LP-MRF method. First, an 8-neighbourhood line process is used to detect discontinuous phase surfaces while regularising continuous phase surface. Then, a truncated quadratic is utilised in the LP model for optimisation convenience. Finally, the proposed method on four types of simulated experimental data is tested, which yields that the proposed method has better performance than some of the commonly used methods in handling sharp phase discontinuities while regularising continuous phase surfaces.

3-D InISAR Imaging of the Ship Target Based on Joint Cross S-Method Algorithm

3-D interferometric inverse synthetic aperture radar (InISAR) imaging of ship targets has always been a hot and difficult issue in research, and how to preserve the interferometric phase while performing high-resolution 2-D ISAR imaging of the complex echoes is the key to 3-D InISAR imaging. In this letter, a novel 3-D InISAR imaging algorithm of the ship target based on joint cross S-method is proposed. First, the azimuth short-time Fourier transform (STFT) is applied to the 1-D range profiles after motion compensation and image coregistration. Then, extract the interferometric phase matrices after performing the joint cross S-method transformation of the STFT results along the two baselines. Besides, the S-method transformations are implemented recursively for the joint cross S-method transformed results to obtain high-resolution ISAR images. Finally, the 3-D InISAR imaging can be achieved by combining the phase matrices and ISAR images at the same time. Simulation results verify the effectiveness and superiority of the proposed algorithm.

Accelerated glacier mass loss (2011–2016) over the Puruogangri ice field in the inner Tibetan Plateau revealed by bistatic InSAR measurements

The temporal variation of glacier mass balance during recent years remains poorly known for the mountain glaciers in the inner Tibetan Plateau (ITP), due to the lack of field measurements. In this study, we retrieved the annual glacier mass balance of the Puruogangri ice field, which is the largest modern ice mass in the ITP, by differencing multi-temporal digital elevation models (DEMs) generated with five pairs of TanDEM-X bistatic interferometric synthetic aperture radar (InSAR) images acquired between April 2011 and January 2016. We compared the TanDEM-X DEMs in January and April 2012 to estimate the X-band radar penetration depth difference (0.61 ± 0.06 m), which enabled systematic bias correction in the estimation of annual glacier mass balance. The observed mass balance reveals a glacier mass gain of 0.44 ± 0.10 m w.e. yr−1 in 2011–12, which was followed by accelerated glacier mass loss in 2012–16. Glacier mass balances of −0.13 ± 0.03, −0.34 ± 0.06, and − 0.52 ± 0.10 m w.e. yr−1 were estimated for the periods of 2012–13, 2013–14, and 2014–16, respectively. This accelerating trend of glacier mass loss is likely caused by the continuous decrease in annual precipitation, according to the climate data recorded by adjacent meteorological stations. This study demonstrates that repeated bistatic InSAR measurement is a promising method for monitoring glacier elevation change and mass balance at regular intervals.

Estimation of Translational Motion Parameters in Terahertz Interferometric Inverse Synthetic Aperture Radar (InISAR) Imaging Based on a Strong Scattering Centers Fusion Technique

Translational motion of a target will lead to image misregistration in interferometric inverse synthetic aperture radar (InISAR) imaging. In this paper, a strong scattering centers fusion (SSCF) technique is proposed to estimate translational motion parameters of a maneuvering target. Compared to past InISAR image registration methods, the SSCF technique is advantageous in its high computing efficiency, excellent antinoise performance, high registration precision, and simple system structure. With a one-input three-output terahertz InISAR system, translational motion parameters in both the azimuth and height direction are precisely estimated. Firstly, the motion measurement curves are extracted from the spatial spectrums of mutually independent strong scattering centers, which avoids the unfavorable influences of noise and the “angle scintillation” phenomenon. Then, the translational motion parameters are obtained by fitting the motion measurement curves with phase unwrapping and intensity-weighted fusion processing. Finally, ISAR images are registered precisely by compensating the estimated translational motion parameters, and high-quality InISAR imaging results are achieved. Both simulation and experimental results are used to verify the validity of the proposed method.

Residual Motion Error Correction with Backprojection Multisquint Algorithm for Airborne Synthetic Aperture Radar Interferometry.

For airborne interferometric synthetic aperture radar (InSAR) data processing, it is essential to achieve precise motion compensation to obtain high-quality digital elevation models (DEMs). In this paper, a novel InSAR motion compensation method is developed, which combines the backprojection (BP) focusing and the multisquint (MSQ) technique. The algorithm is two-fold. For SAR image focusing, BP algorithm is applied to fully use the navigation information. Additionally, an explicit mathematical expression of residual motion error (RME) in the BP image is derived, which paves a way to integrating the MSQ algorithm in the azimuth spatial wavenumber domain for a refined RME correction. It is revealed that the proposed backprojection multisquint (BP-MSQ) algorithm exploits the motion error correction advantages of BP and MSQ simultaneously, which leads to significant improvements of InSAR image quality. Simulation and real data experiments are employed to illustrate the effectiveness of the proposed algorithm.

Experimental Research on Interferometric Inverse Synthetic Aperture Radar Imaging with Multi-Channel Terahertz Radar System.

The all solid-state terahertz (THz) radar has obvious miniaturized integration and high resolution imaging advantages compared with conventional microwave radar. In this paper, a 0.22 THz active frequency-modulated pulse radar system with one transmission channel and four receiving channels is presented, and interferometric inverse synthetic aperture radar (InISAR) imaging experiments, which can acquire altitude information of objects, are carried out. In order to acquire high-quality InISAR images, a calibration method is presented to solve the nonlinearity of wideband signal frequency and phase inconsistency of different receiving channels together. Furthermore, to deal with the phase wrapping in InISAR imaging of objects with large scale, a novel method based on the dominant scatterers to estimate the objects rotation rate is presented. Finally, to show more information of objects in the InISAR images, the imaging results with a large rotation angle by the convolutional back-projection algorithm are obtained. The imaging results verify the superior performance of the multi-channel THz radar system and the imaging processing method, which can provide support for further research on InISAR imaging in the THz band.