Multiple-aperture Interferometry Research Articles

Derivation of 3D Coseismic Displacement Field from Integrated Azimuth and LOS Displacements for the 2018 Hualien Earthquake

A 3D surface deformation field for an earthquake can aid in understanding fault behaviors and earthquake mechanisms. However, SAR-based 3D surface deformation estimates are often limited by insufficient observations and hampered by various error sources. In this study, we demonstrate the derivation of a 3D coseismic displacement field from different InSAR processing algorithms. The azimuth displacements from Multiple Aperture Interferometry (MAI) and Pixel Offset Tracking (POT) were integrated to ensure reliable displacements at low coherent areas. The 3D displacement field was inverted pixel-by-pixel by Line-of-Sight (LOS) displacement and integrated azimuth displacement. The results showed that MAI and POT could compensate for the weaknesses of each algorithm. Also, pixels with less than three sets of observations showed higher noise levels. Such noisy pixels were removed by a denoising criterion proposed herein. For the vertical direction, the proportion of pixels inverted with two sets of azimuth and one set of LOS displacements was 26.1%. After denoising, the proportion dropped to 2.4% due to the insufficiency of LOS displacements. This shows that the viewing angle influences the overall performance of 3D surface displacement inversion. Implementing various displacement vectors should reduce such limitations.

What Triggers Caldera Ring‐Fault Subsidence at Ambrym Volcano? Insights From the 2015 Dike Intrusion and Eruption

AbstractSurface deformation accompanying dike intrusions is dominated by uplift and horizontal motion directly related to the intrusions. In some cases, it includes subsidence due to associated magma reservoir deflation. When reservoir deflation is large enough, it can form, or reactivate preexisting, caldera ring‐faults. Ring‐fault reactivation, however, is rarely observed during moderate‐sized eruptions. On February 21, 2015 at Ambrym volcano in Vanuatu, a basaltic dike intrusion produced more than 1 m of coeruptive uplift, as measured by InSAR, synthetic aperture radar correlation, and Multiple Aperture Interferometry. Here, we show that an average of ∼40 cm of slip occurred on a normal caldera ring‐fault during this moderate‐sized (VEI < 3) event, which intruded a volume of ∼24 × 106 m3 and erupted ∼9.3 × 106 m3 of lava (DRE). Using the 3D Mixed Boundary Element Method, we explore the stress change imposed by the opening dike and the depressurizing reservoir on a passive, frictionless fault. Normal fault slip is promoted when stress is transferred from a depressurizing reservoir beneath one of Ambrym's main craters. After estimating magma compressibility, we provide an upper bound on the critical fraction (f = 7%) of magma extracted from the reservoir to trigger fault slip. We infer that broad basaltic calderas may form in part by hundreds of subsidence episodes no greater than a few meters, as a result of magma extraction from the reservoir during moderate‐sized dike intrusions.

Search Space Reduction for Determination of Earthquake Source Parameters Using PCA and k -Means Clustering

The characteristics of an earthquake can be derived by estimating the source geometries of the earthquake using parameter inversion that minimizes the L2 norm of residuals between the measured and the synthetic displacement calculated from a dislocation model. Estimating source geometries in a dislocation model has been regarded as solving a nonlinear inverse problem. To avoid local minima and describe uncertainties, the Monte-Carlo restarts are often used to solve the problem, assuming the initial parameter search space provided by seismological studies. Since search space size significantly affects the accuracy and execution time of this procedure, faulty initial search space from seismological studies may adversely affect the accuracy of the results and the computation time. Besides, many source parameters describing physical faults lead to bad data visualization. In this paper, we propose a new machine learning-based search space reduction algorithm to overcome these challenges. This paper assumes a rectangular dislocation model, i.e., the Okada model, to calculate the surface deformation mathematically. As for the geodetic measurement of three-dimensional (3D) surface deformation, we used the stacking interferometric synthetic aperture radar (InSAR) and the multiple-aperture SAR interferometry (MAI). We define a wide initial search space and perform the Monte-Carlo restarts to collect the data points with root-mean-square error (RMSE) between measured and modeled displacement. Then, the principal component analysis (PCA) and the k -means clustering are used to project data points with low RMSE in the 2D latent space preserving the variance of original data as much as possible and extract k clusters of data with similar locations and RMSE to each other. Finally, we reduce the parameter search space using the cluster with the lowest mean RMSE. The evaluation results illustrate that our approach achieves 55.1~98.1% reductions in search space size and 60~80.5% reductions in 95% confidence interval size for all source parameters compared with the conventional method. It was also observed that the reduced search space significantly saves the computational burden of solving the nonlinear least square problem.

Rift-parallel block-like motion of the graben floor during the 2005–2010 Afar rifting episode

Crustal deformations associated with rifting episodes are often explained by both normal faulting and tensile opening in an elastic body, suggesting no significant rift-parallel displacements. In this study, using ALOS/PALSAR pixel-offset and multiple aperture interferometry (MAI) data, we detected ~1 m of northwestward block-like cumulative horizontal motion in the graben floor during the latter half of the 2005–2010 Afar rifting episode, Ethiopia. This horizontal block-like motion can be explained by additional shallower strike-slip on normal fault surfaces, which was presumably aseismic due to the very small number of strike-slip earthquakes and a significant gap between seismic and geodetic moment releases. We conclude that the rift-parallel movement can be interpreted by the strain accommodation of plate oblique spreading associated with dike intrusions, as has been demonstrated for the 2014 Bárðarbunga dike intrusion episode. Although we do not propose direct evidence for the plate oblique spreading, the complicated tectonic setting caused by the rotation of the Danakil block and the upwelling plume beneath the Afar triple junction may be drivers of the rift-parallel motion associated with the Afar dike intrusion.

Influence of Orbit and System Parameters on Geosynchronous SAR Multiple-Aperture Interferometry Processing: Analysis and Validation

A geosynchronous synthetic aperture radar (GEO SAR) can achieve a shorter revisit time, a longer observation time, and a larger coverage area for the target scene compared with low earth orbit (LEO) SARs. Therefore, its combination with the multiple-aperture interferometry (MAI) technique can allow along-track deformation measurements with better performance. Nevertheless, because the orbit and system parameters determine the MAI measuring geometry, their influence on the accuracy of such deformation measurements should be extensively studied. In this paper, based on theoretical deductions and simulations, the performance of GEO SAR MAI processing in along-track deformation measurements is discussed considering the orbit and system parameters. The optimal along-track deformation accuracy (OADA) was introduced for quantitative performance evaluations. Finally, a repeat-track global navigation satellite system-based SAR MAI experiment, implemented with a transponder onboard displacement device on the ground and BeiDou-2 inclined geosynchronous orbit satellites, was conducted to verify the effectiveness of the proposed method and its validating analysis. The results suggested that the OADA could be improved by decreasing the azimuth antenna size or the ratio between the averaged velocities of beam footprint and satellite, mainly depending on the inclination, eccentricity, and look angle.

Surface deformation and source modeling of Ayaz-Akhtarma mud volcano, Azerbaijan, as detected by ALOS/ALOS-2 InSAR

Azerbaijan, located on the western edge of the Caspian Sea in Central Asia, has one of the highest populations of mud volcanoes in the world. We used satellite-based synthetic aperture radar (SAR) images derived from two L-band SAR satellites, ALOS/PALSAR along an ascending track from 2006 to 2011, and its successor ALOS-2/PALSAR-2 along both ascending and descending tracks from 2014 to 2017. First, we applied interferometric SAR (InSAR) technique to detect surface displacements at the Ayaz-Akhtarma mud volcano in Azerbaijan. The 35 derived interferograms indicate that the deformation of the mud volcano is largely characterized by horizontal displacement. Besides the InSAR technique, we also used multiple-aperture interferometry (MAI) to derive the surface displacements parallel to the satellite flight direction to complement the InSAR data. Using the InSAR and MAI data, we obtained 3D displacements, which indicate that the horizontal displacement is dominant relative to subsidence and possible uplift. To explain the displacements, we performed source modeling, based on the assumption of elastic dislocation theory in a half space. The derived model consists of a convex surface on which normal-fault-type slips are semi-radially distributed, causing the significant horizontal displacements with minor subsidence. The convex source surface suggests that a steady overpressure system would be maintained by constantly intruding mud and gas.

Advances in three-dimensional deformation mapping from satellite radar observations: application to the 2003 Bam earthquake

ABSTRACTThe advance of the surface deformation measurement from synthetic aperture radar interferometry (InSAR) provides an opportunity of reinterpretation for the past controversial event in the geoscience community. According to the development of the multiple-aperture interferometry (MAI) method, three-dimensional (3D) surface displacements can be estimated with few centimetres accuracy by integrating InSAR and MAI observations. In this study, we provided a renewed fault model of the 2003 Bam earthquake using the advanced method. The 3D deformation map showed the clear distribution pattern of the right-lateral strike-slip fault as well as the additional information of an asymmetry of the surface deformation. To determine the optimal model parameters, we employed a two-segment fault model considering the multiple segments. As a result, two sub-parallel fault segments showing N-S trend were obtained. The model parameters of the second segment have relatively large uncertainties though, the first segment which is presumed as the causative fault of the Bam event has been well-modelled with precise model parameters. The more constrained fault model based on the 3D deformation field enabled us to suggest a possibility of a new interpretation and the better understanding of the fault behaviour.

Mapping three-dimensional surface deformation caused by the 2010 Haiti earthquake using advanced satellite radar interferometry.

Mapping three-dimensional (3D) surface deformation caused by an earthquake is very important for the environmental, cultural, economic and social sustainability of human beings. Synthetic aperture radar (SAR) systems made it possible to measure precise 3D deformations by combining SAR interferometry (InSAR) and multiple aperture interferometry (MAI). In this paper, we retrieve the 3D surface deformation field of the 2010 Haiti earthquake which occurred on January 12, 2010 by a magnitude 7.0 Mw by using the advanced interferometric technique that integrates InSAR and MAI data. The surface deformation has been observed by previous researchers using the InSAR and GPS method, but 3D deformation has not been measured yet due to low interferometric coherence. The combination of InSAR and MAI were applied to the ALOS PALSAR ascending and descending pairs, and were validated with the GPS in-situ measurements. The archived measurement accuracy was as little as 1.85, 5.49 and 3.08 cm in the east, north and up directions, respectively. This result indicates that the InSAR/MAI-derived 3D deformations are well matched with the GPS deformations. The 3D deformations are expected to allow us to improve estimation of the area affected by the 2010 Haiti earthquake.

Multi-track extraction of two-dimensional surface velocity by the combined use of differential and multiple-aperture InSAR in the Amery Ice Shelf, East Antarctica

Glaciers and ice streams drain the ice from the ice sheets to the ice shelves, and contribute to global sea-level changes. Therefore, ice velocity is an essential parameter for the assessment of mass balance. In this paper, we propose an approach for the multi-track extraction of two-dimensional ice surface velocity by the combined use of multiple-aperture interferometry (MAI) and differential synthetic aperture radar interferometry (DInSAR). The azimuth and ground range ice movements of each individual track are first estimated by the use of MAI and DInSAR, respectively. A seamless two-dimensional ice velocity map is then achieved by calibration and mosaicking of the estimated velocity of the multi-temporal and multi-track measurements over a large area. Finally, the dynamic behavior of the Amery Ice Shelf is analyzed by formulating a long-term series of ice flow velocities consisting of historical surface velocities (1968–1990), the estimated surface velocity by the proposed method with ERS-1/2 data (1996), existing surface velocity products such as the Radarsat-1 Antarctic Mapping Project (RAMP) velocities (1997–2000) and Rignot's results (2007–2010), as well as the estimated velocities obtained by the use of the offset tracking method from Landsat 8 images (2013–2014). The results show that the estimated velocity obtained by the use of the proposed method is superior to the other methods, and the long-term series of ice velocity measurements shows that the ice velocity in the Amery Ice Shelf has hardly changed over the past 45years (1968–2014). We conclude that the ice flow velocity of the Amery Ice Shelf has showed a slight deceleration over the past 45years.

A method of monitoring three-dimensional ground displacement in mining areas by integrating multiple InSAR methods

ABSTRACTUnderground mining often causes large-gradient vertical and horizontal displacement in ground surface, resulting in the losses of coherence and difficulties in phase unwrapping. This article presents an approach to determine three-dimensional ground displacements in mining areas with the large gradient or phase decorrelation by integrating multiple interferometric synthetic aperture radar (InSAR) methods. The core of the proposed method is that the offset-tracking method is employed to solve for the displacement with the large gradient or phase decorrelation. First, the displacements in the radar line-of-sight directions are obtained from two interferometric pairs with different viewing geometries by integrating the measurements of differential InSAR and offset tracking. Then, the displacements in the azimuthal directions are obtained from two interferometric pairs with different viewing geometries by integrating the measurements of multiple aperture interferometry and offset tracking. Finally, the three-dimensional ground displacement fields are inferred from these four independent, one-dimensional displacements using the least squares method and Helmert variance component estimation. We apply this method to obtain the three-dimensional ground displacement field in the Dongtan mine region. We compare the results with those of levelling and global positioning system surveys, and the root mean square errors of the results were 24 and 43 mm in the vertical direction and horizontal directions, respectively. The experimental results indicate that the proposed method can be used to estimate three-dimensional ground displacement fields in mining areas with large-gradient displacement and phase decorrelation.

Three-Dimensional Deformation Retrieval in Geosynchronous SAR by Multiple-Aperture Interferometry Processing: Theory and Performance Analysis

The 3-D deformation retrieval is significant for the accurate evaluation of geologic disasters (e.g., earthquakes and landslides). Multiple-aperture interferometry (MAI) is an effective method to obtain 3-D deformation, combined with the cross-heading tracks synthetic aperture radar (SAR) data. However, because of the limitations of the low earth orbit SAR, a long satellite revisit time, small common areas of the cross-heading tracks data, and the unsatisfied along-track deformation measurement accuracy usually exist in the traditional MAI 3-D deformation retrieval. Geosynchronous SAR (GEO SAR) runs in the geosynchronous orbit, which has the advantages of a large observation area and a short revisit time. This paper focuses on 3-D deformation retrieval by GEO SAR MAI processing. Aiming at the high orbit and the squint looking of GEO SAR, the accurate expressions of the along-track deformation, 3-D deformation, and the errors in GEO SAR MAI processing are given. The distortions and their correction in the MAI interferogram brought by the geometrical difference between the forward- and backward-looking interferograms and the multicycles flat-earth and topographic phases are given. Moreover, an optimal subaperture selection method based on minimum position dilution of precision is proposed. Finally, the effectiveness of the proposed method is validated by simulations and the experiment of BeiDou-2 inclined geosynchronous orbit navigation satellite. The theoretical analysis and the experimental results suggest centimeter-level and even millimeter-level deformation measurement accuracy could be obtained in 3-D by GEO SAR MAI processing.

Remarks on correcting ionospheric distortions in L-band radar interferometry

The L-band synthetic aperture radar (SAR) interferometry (InSAR) technique has a lower accuracy due to ionospheric phase distortions. Recently, a multiple-aperture interferometry (MAI)-based ionospheric correction method has been proposed. Using four types of ionosphere-distorted interferograms, the performance of the correction method was evaluated and then analyzed the feasibility of the correction method. The test interferograms contained severe azimuth streaking, low-frequency ionospheric phase distortion and drastic phase change due to the ionosphere. The results showed that (i) the existence and magnitude of ionospheric phase distortions can be recognized from MAI interferograms and (ii) the MAI-based ionospheric correction method efficiently reduced severe azimuth streaking and low-frequency distortion but did not mitigate the drastic phase change perfectly. It is allowed (i) to determine whether a given SAR interferogram has an ionospheric distortion and (ii) to predict whether the ionospheric distortion can be corrected by using the MAI-based ionospheric correction method.

An improved data integration algorithm to constrain the 3D displacement field induced by fast deformation phenomena tested on the Napa Valley earthquake

In this work, we propose an improved algorithm to constrain the 3D ground displacement field induced by fast surface deformations due to earthquakes or landslides. Based on the integration of different data, we estimate the three displacement components by solving a function minimization problem from the Bayes theory. We exploit the outcomes from SAR Interferometry (InSAR), Global Positioning System (GNSS) and Multiple Aperture Interferometry (MAI) to retrieve the 3D surface displacement field. Any other source of information can be added to the processing chain in a simple way, being the algorithm computationally efficient. Furthermore, we use the intensity Pixel Offset Tracking (POT) to locate the discontinuity produced on the surface by a sudden deformation phenomenon and then improve the GNSS data interpolation. This approach allows to be independent from other information such as in-situ investigations, tectonic studies or knowledge of the data covariance matrix. We applied such a method to investigate the ground deformation field related to the 2014 Mw 6.0 Napa Valley earthquake, occurred few kilometers from the San Andreas fault system.

Two-Dimensional Deformation Measurement Based on Multiple Aperture Interferometry in GB-SAR

Ground-based synthetic aperture radar (GB-SAR) technique has been widely applied for the deformation monitoring and measurement of the natural and engineered slopes. To extend the 2-D deformation measurement from the conventional 1-D measurement along the radar-target line of sight (LOS), multiple aperture interferometry (MAI) techniques based on phase differences between interferograms of the forward-looking and backward-looking subapertures are tackled in this letter. The optimal subaperture selection is analyzed considering the typical signal-to-noise ratios and correlations in GB-SAR applications. Simulations prove that the coherent integration (CIM) can be utilized to improve the measurement accuracy of the MAI method. Besides, GB-SAR experiments are carried out to validate the feasibility and effectiveness of the 2-D deformation measurement method based on MAI. Accuracy comparison of deformation measurement with the MAI and cross correlation methods is also taken. Experimental results show that the accuracy of deformation measurement along the perpendicular direction to LOS based on MAI and CIM can reach millimeter level for displaceable corner reflector.

Mapping Three-Dimensional Co-Seismic Deformations Fields by Combining Multiple-Aperture Interferometry and Differential Interferometric Synthetic Aperture Radar Techniques

DInSAR technique based displacement measurement is sensitive to only radar line-of-sight, which renders it hard to determine 3D co-seismic deformations. To infer these deformations, a method based on the robust least squares method by combining the multiple-aperture interferometry (MAI) and DInSAR is applied to one ascending and one descending interferometric pair for the 2003 Bam, Iran, earthquake. The results reveal that co-seismic deformations not has the level strike-slip in north-south direction, but also has a large vertical component and a horizontal component in east-west direction. In areas with high interferometry coherence (>0.6), the standard deviation of MAI results is less than 0.075 m, and the 3D deformations are consistent with results of combining DInSAR and Offset Tracking technology in up-down and east-west directions with the maximum difference of 0.031 m. But the differences in south-north direction are relatively large on decimeter level. Therefore, the proposed method can be used to model reliable and accurate 3D surface displacement fields and benefit for analyzing the causes and effects of the earthquake.

Simulation of the SuperSAR Multi-Azimuth Synthetic Aperture Radar Imaging System for Precise Measurement of Three-Dimensional Earth Surface Displacement

The SuperSAR imaging system, a novel multi-azimuth synthetic aperture radar (SAR) system capable of detecting Earth surface deformation in three dimensions from a single satellite platform, has recently been proposed. In this paper, we investigate the feasibility of detecting precise 3-D surface displacement measurements with the SuperSAR imaging system using a point target simulation. From this simulation, we establish both a relationship between the interferometric SAR phase and the across-track displacement and a relationship between the multiple-aperture interferometry phase and the along-track displacement based on the SuperSAR imaging geometry. The theoretical uncertainties of the SuperSAR measurement are analyzed in the across- and along-track directions, and the theoretical accuracy of the 3-D displacement measurement from the SuperSAR system is also investigated according to both the decorrelation and the squint and look angles. In the case that the interferometric coherence is about 0.8 and that five effective looks are employed, the theoretical 2-D measurement precision values are about 3.67 and 6.35 mm in the across- and along-track directions, respectively, and the theoretical 3-D measurement precision values for 3-D displacement are about 4.05, 4.56, and 3.45 mm in the east, north, and up directions, respectively. The result of this study demonstrates that the SuperSAR imaging system is capable of measuring the 3-D surface displacement in all directions with subcentimeter precision.

An integrated method based on DInSAR, MAI and displacement gradient tensor for mapping the 3D coseismic deformation field related to the 2011 Tarlay earthquake (Myanmar)

Abstract The satellite differential interferometric synthetic aperture radar (DInSAR) technology has been widely applied for mapping the ground deformation associated with the geophysical events such as earthquakes. However, the conventional DInSAR can measure only the one-dimensional (1D) ground displacement along the radar line of sight (LOS), and the crucial displacement measurements, e.g., near the epicenter and along the surface ruptures, are usually not available or degraded in quality due to the significant deformation gradients. With availability of satellite SAR images acquired along ascending and descending orbits, this paper proposes an integrated method to map the three-dimensional (3D) coseismic deformation field by combining DInSAR for detecting LOS displacements, the multiple aperture interferometry (MAI) for detecting along-track displacements, and the displacement gradient tensor (DGT) model for characterizing spatial correlation of ground displacements. The proposed method (termed as InSAR–DGT) was first tested through an experiment of recovering 3D displacements from a simulated coseismic deformation field. We then applied the proposed method to map the 3D coseismic deformation field related to the 2011 Tarlay earthquake (Myanmar) by using the ascending and descending ALOS PALSAR images. Both the results derived for the simulated experiment and the 2011 Tarlay earthquake show that the quality of the 3D coseismic displacements can be raised efficiently by the InSAR–DGT method, and the precisions in the east–west (E–W), north–south (N–S) and up–down (U–D) displacements for the 2011 Tarlay earthquake are increased 22%, 36% and 24%, respectively. The validation indicates that the improved coseismic deformation field for the 2011 Tarlay earthquake is in good agreement with the deformation field simulated from the existing optimized fault model. The number of the missing data points in the 3D coseismic deformation field can be reduced significantly by the InSAR–DGT method. It is revealed that the causative fault (i.e., the west part of the Nam Ma Fault) for the Tarlay earthquake generated a left-lateral slip that was accompanied by a minor normal dip-slip component. The careful interpretation demonstrates that the causative fault structures include the determined main fault segment and the two suspected branched segments at east of the Tarlay town.

An Improvement of Ionospheric Phase Correction by Multiple-Aperture Interferometry

Recently a multiple-aperture interferometry (MAI)-based azimuth shift method has been proposed to correct the ionospheric phase on synthetic aperture radar (SAR) interferograms. This method needs to determine integral constants required for azimuth integration. The exact estimation of the integral constants plays a key role in this MAI-based method. In this paper, we propose an efficient method for improving the performance of integral constant estimation, which functions by simultaneously removing the ionospheric and orbital phase artifacts from the interferometric SAR interferogram. We validate the performance improvement of the proposed method using two Advanced Land Observation Satellite Phase Array L-band SAR (ALOS PALSAR) interferometric pairs. The proposed method is compared with a MAI-based method, which does not work well due to azimuth integration errors. The proposed method successfully corrects the ionospheric and orbital phase artifacts. In addition, we compare the performances of the previous and proposed methods using the in situ Global Positioning System velocities. The root-mean-square error (RMSE) in line-of sight velocity from the previous method is about 7.0 mm/yr, whereas the RMSE from the proposed method is about 4.3 mm/yr. An RMSE reduction of about 38.6% is achieved when using the proposed method. These results indicate: 1) that the proposed method successfully estimates and corrects the ionosphere and orbital phase distortions; and 2) that the proposed method is superior to the previous method.

Measurement of three-dimensional surface deformation by Cosmo-SkyMed X-band radar interferometry: Application to the March 2011 Kamoamoa fissure eruption, Kīlauea Volcano, Hawai'i

Abstract Three-dimensional (3D) surface deformation is retrieved for the March 6–10, 2011 (UTC dates), Kamoamoa fissure eruption along the East Rift Zone of Kīlauea Volcano, Hawai'i, through the integration of multi-temporal synthetic aperture radar (SAR) interferometry (InSAR) and multiple-aperture interferometry (MAI) measurements from the COSMO-SkyMed X-band SAR. The measurement accuracies of 1) the individual and multi-stacked MAI interferograms and 2) the 3D deformation, which is measured from COSMO-SkyMed data, are assessed using continuous GPS stations. The root-mean-square (RMS) errors of individual MAI interferograms for descending and ascending data are 2.97 ± 0.6 cm and 3.20 ± 0.62 cm, respectively. The MAI interferograms stacked from multi-temporal observations can produce better results by emphasizing surface deformation signals, with the RMS errors of 1.06 and 1.24 cm for descending and ascending data, respectively. The empirical equations for measurement uncertainties are determined with respect to interferometric coherence for individual and stacked MAI interferograms. An assessment of the 3D components of deformation was performed as well, and RMS errors of 0.75, 0.83, and 0.68 cm were estimated in the east, north, and up directions. A performance test of magma source model parameter estimations was carried out by using the InSAR and 3D measurements. From the 3D deformation field, we found that the magma chamber source at the Kīlauea caldera should be modeled by the spheroid source rather than the simple point source. The performance comparison between the InSAR and 3D modeled results showed that the 3D deformation field allows for precise model parameter estimation.

An Improvement of Multiple-Aperture SAR Interferometry Performance in the Presence of Complex and Large Line-of-Sight Deformation

Synthetic Aperture Radar Interferometry (InSAR) provides one-dimensional measurements on ground displacement in the radar line-of-sight (LOS) direction. Multiple-Aperture Interferometry (MAI) technique has been successfully used to measure along-track ground displacement. However, the technique occasionally shows filtering boundary artifacts along the boundary of incoherent areas and a loss of MAI coherence in the presence of large and complex LOS deformation. In this study, we propose an efficient MAI processing method to mitigate them and improve computational efficiencies as well. We validated the performance of the proposed MAI method using ALOS PALSAR interferometric pair acquired from the ascending orbits on June 12, 2007 and August 2, 2009. The test pair includes large and complex LOS deformation signals accumulated from several dike intrusions and fissure eruptions. Through the proposed MAI processing method, we have generated the InSAR and MAI interferograms with the pixel spacing of about 45 and 40 m in ground range and azimuth directions, respectively. Close to surface rupture, we found that our proposed method improved the MAI coherence from 0.33 to 0.96 and reduced the filtering boundary artifacts from 0.068 to 0.040 rad. The results demonstrate the potential of the proposed method to measure along-track ground displacement in regions of decorrelation.