Interferometric Synthetic Aperture Radar Method Research Articles

Surface deformation monitoring of Sinabung volcano using multi temporal InSAR method and GIS analysis for affected area assessment

Sinabung Volcano which located in northern part of Sumatera island is part of a hundred active volcano in Indonesia. Surface deformation is detected over Sinabung Volcano and surrounded area since the first eruption in 2010 after 400 years long rest. We present multi temporal Interferometric Synthetic Aperture Radar (InSAR) time-series method of ALOS-2 L-band SAR data acquired from December 2014 to July 2017 to reveal surface deformation with high spatial resolution. The method includes focusing the SAR data, generating interferogram and phase unwrapping using SNAPHU tools. The result reveal significant deformation over Sinabung Volcano areas at rates up to 10 cm during observation period and the highest deformation occurs in western part which is trajectory of lava. We concluded the observed deformation primarily caused by volcanic activity respectively after long period of rest. In addition, Geographic Information System (GIS) analysis produces disaster affected areas of Sinabung eruption. GIS is reliable technique to estimate the impact of the hazard scenario to the exposure data and develop scenarios of disaster impacts to inform their contingency and emergency plan. The GIS results include the estimated affected area divided into 3 zones based on pyroclastic lava flow and pyroclastic fall (incandescent rock and ash). The highest impact is occurred in zone II due to many settlements are scattered in this zone. This information will be support stakeholders to take emergency preparation for disaster reduction. The continuation of this high rate of decline tends to endanger the population in next periods.

Spatial and temporal variations in subsidence due to the natural consolidation and compaction of sediment in the yellow river delta, china

ABSTRACTThe Yellow River Delta, which is the second-largest delta in China, has experienced varying degrees of land subsidence since the late 1970s. Although recent studies have identified the natural consolidation and compaction of sediment among the most important contributors to geologic processes, their processes have rarely been quantified. We estimated the sediment compaction over different time ranges to determine the temporal evolution of subsidence parameters (i.e., cumulative compaction). Estimates of primary consolidation, secondary consolidation, and the degree of consolidation in 152 boreholes revealed the spatial–temporal characteristics of sediment compaction and consolidation using geotechnical parameters collected from 152 boreholes, soil mechanics equations and the Kriging interplolation method. In addition, these estimates were partially constrained and cross-validated using the interferometric synthetic aperture radar (InSAR) results from early 2007 to late 2010 which were provided in a previous study. By performing a comparison analysis between theoretical evaluations of compaction for borehole data and InSAR observations, we were able to quantify subsidence due to sediment compaction. The comparison results suggest that the theoretical solutions agreed well with the measurements recorded by the well-validated, advanced InSAR method and that the deviations between the InSAR technique and geotechnical evaluations ranged from −22 to 3 mm. The results reveal that the land subsidence of the chosen borehole sites during the investigative period was dominated by the primary consolidation and compaction of sediment. The underprediction of subsidence may be explained by fluid withdrawal, oil exploitation and engineering construction. To speculate, more geological disasters may occur if the current subsidence condition extends into the future.

Feasibility of ALOS2 PALSAR2 Offset-Based Phase Unwrapping of SAR Interferogram in Large and Complex Surface Deformations

The interferometric synthetic aperture radar (InSAR) is a well-known tool for mapping ground surface deformations with centimeter precision, and is much better than that used in the offset tracking method. However, the InSAR method has difficulties in precisely measuring large deformation signals because the phase unwrapping can include severe errors in the case of large and complex deformations. To overcome this drawback, an offset-based unwrapping strategy was proposed. However, this strategy has almost never been used for the unwrapping approach because the accuracy of offset measurement is much lower than that of InSAR measurement. As the spatial resolution of the SAR image becomes more precise, the offset measurement accuracy increases. Specifically, the L-band ALOS2 PALSAR2 sensor has much higher offset measurement accuracy due to its higher spatial resolution. In this paper, the feasibility of the unwrapping of a PALSAR-2 interferometric phase with large surface deformation signals, using an offset map, is proved. This validation of offset-based unwrapping was performed using two ALOS2 PALSAR2 co-seismic pairs in the 2016 Kumamoto earthquake where large deformations of more than 200 cm occurred. The offset-based unwrapping was more successful than traditional unwrapping. The root-mean square errors of offset-based unwrapping using GPS in situ data were about 1.96 and 1.90 cm in the ascending and descending pairs, respectively. The validation results showed that the ALOS2 PALSAR2 offset-based unwrapping enables us to measure complex and large deformation signals accurately. Precise measurements in high-gradient and high-decorrelated deformation areas would be helpful to better understand geological mechanisms.

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.

Analyses of surface deformation with SBAR InSAR method and its relationship with aquifer occurrence in Surabaya City, East Java, Indonesia

Rapid development of Surabaya City requires space for industry and settlement. The city development is followed by increasing of water demand for various purposes. Large amount of groundwater extraction may cause ground subsidence. According to groundwater extraction, we tried to delineate the possibility of aquifer potential based on ground surface deformation using Interferometric Synthetic Aperture Radar (InSAR) and Electrical Resistivity methods. The InSAR is a method to estimate surface deformation in millimeter scale based on different phase of SAR data between acquisition times. In this paper, surface deformation combined with ground resistivity was used to analyse the potential of aquifer related to subsidence at Surabaya City, East Java, Indonesia. The Small Based Subset (SBAS) method was used to reduce phase delayed in the interferogram due to atmospheric condition. Based on the SBAS InSAR the deformation was detected at Surabaya City in January 2007 to February 2008. The largest and lowest deformation about 40 mm/year and about 0-10 mm/year were located in North to Southeastern and Western part of the city, respectively. The geodetic Global Positioning System (GPS) campaign in Surabaya confirmed that the detected deformation correlated with the ground subsidence with correlation coefficient about 0.96. To obtain the subsurface structures at subsidence zones, the Electrical Resistivity survey with Schlumberger configuration was performed in Surabaya city. According to the SBAS InSAR and subsurface resistivity, the subsidence around Pabeancantikan, Kenjeran, Simokerto and Tenggilismejoyo sub-districts agreed to high resistivity about 7-18 Ωm. The Sandstone of Kabuh and Pucangan formations in this area served as ground water aquifer which used by more than 200 wells. Ground water extraction probably triggered the subsidence at ground surface. The high resistivity at subsidence zones originated from high porosity of rocks served as aquifer with high groundwater extraction.

Separating volcanic deformation and atmospheric signals at Mount St. Helens using Persistent Scatterer InSAR

Over the past two decades, GPS and leveling surveys have recorded cycles of inflation and deflation associated with dome building eruptions at Mount St. Helens. Due to spatial and temporal limitations of the data, it remains unknown whether any deformation occurred prior to the most recent eruption of 2004, information which could help anticipate future eruptions. Interferometric Synthetic Aperture Radar (InSAR), which boasts fine spatial resolution over large areas, has the potential to resolve pre-eruptive deformation that may have occurred, but eluded detection by campaign GPS surveys because it was localized to the edifice or crater. Traditional InSAR methods are challenging to apply in the Cascades volcanic arc because of a combination of environmental factors, and past attempts to observe deformation at Mount St. Helens were unable to make reliable observations in the crater or on much of the edifice.In this study, Persistent Scatterer InSAR, known to mitigate issues of decorrelation caused by environmental factors, is applied to four SAR data sets in an attempt to resolve localized sources of deformation on the volcano between 1995 and 2010. Many interferograms are strongly influenced by phase delay from atmospheric water vapor and require correction, evidenced by a correlation between phase and topography. To assess the bias imposed by the atmosphere, we perform sensitivity tests on a suite of atmospheric correction techniques, including several that rely on the correlation of phase delay to elevation, and explore approaches that directly estimate phase delay using the ERA-Interim and NARR climate reanalysis data sets. We find that different correction methods produce velocities on the edifice of Mount St. Helens that differ by up to 1cm/yr due to variability in how atmospheric artifacts are treated in individual interferograms. Additionally, simple phase-based techniques run the risk of minimizing any surface deformation signals that may themselves be correlated with elevation. The atmospherically corrected PS InSAR results for data sets overlapping in time are inconsistent with one another, and do not provide conclusive evidence for any pre-eruptive deformation at a broad scale or localized to the crater or edifice leading up to the 2004 eruption. However, we cannot rule out the possibility of deformation less than ~1cm/yr, or discern whether deformation rates increased in the months preceding the eruption. The results do significantly improve the spatial density of observations and our ability to resolve or rule out models for a potential deformation source for the pre-eruptive period.

Exploitation of the Intermittent SBAS (ISBAS) algorithm with COSMO-SkyMed data for landslide inventory mapping in north-western Sicily, Italy

A large scale study of landslide processes was undertaken by coupling conventional geomorphological field surveys with aerial photographs along with an advanced Interferometric Synthetic Aperture Radar (InSAR) analysis of ground instability in north-western Sicily. COSMO-SkyMed satellite images for the period between 2008 and 2011 were processed using the Intermittent Small BAseline Subset (ISBAS) technique, recently developed at the Department of Civil Engineering of the University of Nottingham. The use of ISBAS allowed the derivation of ground surface displacements across non-urbanized areas, thus overcoming one of the main limitations of conventional interferometric techniques. ISBAS provides ground motion information not only for urban but also for rural, woodland, grassland and agricultural terrains, which cover >60% of north-western Sicily, thereby improving by 40 times in some cases, the slope instability investigation capabilities of InSAR methods.ISBAS ground motion data enabled the updating of the landslide inventory for the areas of Piana degli Albanesi and Marineo (over 130km2), which encompass a number of active, dormant and inactive landslides according to the pre-existing landslide inventory maps produced through aerial photo-interpretation and local field checks. An average of ∼7000 ISBASpixelskm−2 allowed the detection of small displacements in regions difficult to access. In particular, 226 landslides – mainly slides, flows and creep and four badlands were identified, comprising a total area of 25.3km2. When compared to the previous landslide inventory maps, 84 phenomena were confirmed, 67 new events were detected and 79 previously mapped events were re-assessed, modifying their typology, boundary and/or state of activity. Because the InSAR method used here is designed to measure slow rates of velocity and therefore may not detect fast-moving, events such as falls and topples, the results for Piana degli Albanesi and Marineo demonstrate the validity of this method to support land management, underlying the time and cost benefits of a combined approach using traditional monitoring procedures and satellite InSAR methods especially if slow-moving slope movements prevail.

Surface creep on the North Anatolian Fault at Ismetpasa, Turkey, 1944–2016

AbstractWe reevaluate the 72 year history of surface slip on the North Anatolian Fault at Ismetpasa since the Mw = 7.4 1944 Bolu/Gerede earthquake. A revised analysis of published observations suggests that days after the earthquake the fault had been offset by 3.7 m and 6 years later by an additional 0.74 m. Creep was first recognized on the fault in 1969 as a 0.13 m offset of a wall constructed in 1957 that now (2016) has been offset by 0.52 m. A carbon rod creep meter operated across the fault in the past 2 years confirms results from an invar wire creep meter operated 1982–1991 that surface slip is episodic. Months of fault inactivity are interrupted by slow slip (≤10 µm/d) or multiple creep events with cumulative amplitudes of 2–10 mm, durations of several weeks, and with slip rates briefly exceeding >2.5 mm/h. Creep events accommodate 80% of the surface slip and individually release ≈ 10−6 shear strain on the flanks of the uppermost 3–7 km of the fault. GPS and interferometric synthetic aperture radar methods yield a current fault slip rate of 7.6 ± 1 mm/yr suggesting that creep meters incompletely sample the full width of the surface shear zone. The slip rate has slowed from >10 mm/yr in 1969 to 6.1 mm/yr at present, 4.65 mm/yr of which appears to be due to steady interseismic creep driven by plate boundary stressing rates. We calculate that a further 1 m of aseismic surface slip will precede the next major earthquake on the fault assuming an ≈ 260 year main shock recurrence interval on this segment.

Sustainable Surface Deformation Related with 2006 Augustine Volcano Eruption in Alaska Measured Using GPS and InSAR Techniques

Augustine volcano, located along the Aleutian Arc, is one of the most active volcanoes in Alaska and nearby islands, with seven eruptions occurring between 1812 and 2006. This study monitored the surface displacement before and after the most recent 2006 eruption. For analysis, we conducted a time-series analysis on data observed at the permanent GPS(Global Positioning System) observation stations in Augustine Island between 2005 and 2011. According to the surface displacement analysis results based on GPS data, the movement of the surface inflation at the average speed of 2.3 cm/year three months prior to the eruption has been clearly observed, with the post-eruption surface deflation at the speed of 1.6 cm/year. To compare surface displacements measurement by GPS observation, ENVISAT(Environmental satellite) radar satellite data were collected between 2003 and 2010 and processed the SBAS(Small Baseline Subset) method, one of the time-series analysis techniques using multiple InSAR(Interferometric Synthetic Aperture Radar) data sets. This result represents 0.97 correlation value between GPS and InSAR time-series surface displacements. This research has been completed precise surface deformation using GPS and time-series InSAR methods for a detection of precursor symptom on Augustine volcano.

Landslide mapping and monitoring by using radar and optical remote sensing: Examples from the EC-FP7 project SAFER

This paper focuses on the Landslide Thematic services of the EU-funded FP7-SPACE project SAFER (Services and Applications For Emergency Response) for inventory mapping, monitoring and rapid mapping by using Earth Observation (EO). We exploited satellite Interferometric Synthetic Aperture Radar (InSAR) and Object-Based Image Analysis (OBIA), and discuss example applications in South Tyrol and Abruzzo (Italy), Lower Austria (Austria), Lubietova (Slovakia) and the Kaohsiung County (Taiwan). These case studies showcase the significance of radar and optical EO data, InSAR and OBIA methods for landslide mapping and monitoring in different geological environments and during all phases of emergency management: mitigation, preparedness, crisis and recovery.

Remote Sensing of Deformation of a High Concrete-Faced Rockfill Dam Using InSAR: A Study of the Shuibuya Dam, China

Settlement is one of the most important deformation characteristics of high concrete faced rockfill dams (CFRDs, >100 m). High CFRDs safety would pose a great threat to the security of people’s lives and property downstream if this kind of deformation were not to be measured correctly, as traditional monitoring approaches have limitations in terms of durability, coverage, and efficiency. It has become urgent to develop new monitoring techniques to complement or replace traditional monitoring approaches for monitoring the safety and operation status of high CFRDs. This study examines the Shuibuya Dam (up to 233.5 m in height) in China, which is currently the highest CFRD in the world. We used space-borne Interferometric Synthetic Aperture Radar (InSAR) time series to monitor the surface deformation of the Shuibuya Dam. Twenty-one ALOS PALSAR images that span the period from 28 February 2007 to 11 March 2011 were used to map the spatial and temporal deformation of the dam. A high correlation of 0.93 between the InSAR and the in-situ monitoring results confirmed the reliability of the InSAR method; the deformation history derived from InSAR is also consistent with the in-situ settlement monitoring system. In addition, the InSAR results allow continuous investigation of dam deformation over a wide area that includes the entire dam surface as well as the surrounding area, offering a clear picture continuously of the dam deformation.

StaMPS Improvement for Deformation Analysis in Mountainous Regions: Implications for the Damavand Volcano and Mosha Fault in Alborz

Interferometric Synthetic Aperture Radar (InSAR) capability to detect slow deformation over terrain areas is limited by temporal decorrelation, geometric decorrelation and atmospheric artefacts. Multitemporal InSAR methods such as Persistent Scatterer (PS-InSAR) and Small Baseline Subset (SBAS) have been developed to deal with various aspects of decorrelation and atmospheric problems affecting InSAR observations. Nevertheless, the applicability of both PS-InSAR and SBAS in mountainous regions is still challenging. Correct phase unwrapping in both methods is hampered due to geometric decorrelation in particular when using C-band SAR data for deformation analysis. In this paper, we build upon the SBAS method implemented in StaMPS software and improved the technique, here called ISBAS, to assess tectonic and volcanic deformation in the center of the Alborz Mountains in Iran using both Envisat and ALOS SAR data. We modify several aspects within the chain of the processing including: filtering prior to phase unwrapping, topographic correction within three-dimensional phase unwrapping, reducing the atmospheric noise with the help of additional GPS data, and removing the ramp caused by ionosphere turbulence and/or orbit errors to better estimate crustal deformation in this tectonically active region. Topographic correction is done within the three-dimensional unwrapping in order to improve the phase unwrapping process, which is in contrast to previous methods in which DEM error is estimated before/after phase unwrapping. Our experiments show that our improved SBAS approach is able to better characterize the tectonic and volcanic deformation in the center of the Alborz region than the classical SBAS. In particular, Damavand volcano shows an average uplift rate of about 3 mm/year in the year 2003–2010. The Mosha fault illustrates left-lateral motion that could be explained with a fault that is locked up to 17–18 km depths and slips with 2–4 mm/year below that depth.

InSAR-derived digital elevation models for terrain change analysis of earthquake-triggered flow-like landslides based on ALOS/PALSAR imagery

Earthquakes can directly trigger multiple simultaneous slope failures in mountainous regions. Among these slope failures, flow-like landslides with high velocities and long run-outs can result in damage that is more destructive than other types of landslides. Timely and accurate recognition of the locations and magnitudes of flow-like landslides is essential for post-disaster relief. Synthetic aperture radar (SAR) sensors are suitable for deformation monitoring because of their capability to operate at day or night and in all weather conditions. Interferometric synthetic aperture radar (InSAR) is an advanced technique that extracts three-dimensional terrain and changes information from the radar images at a regional scale. The focus of this study is the Donghekou landslide-debris flow that was triggered by the 2008 Wenchuan earthquake. ALOS/PALSAR remote satellite images were interpreted by InSAR to generate digital surface elevation models. A comparison of data from a typical InSAR configuration with field survey data proves that the former is an effective method for rapidly detecting flow-like landslides in a mountainous area. The comparison also shows that the accuracy of the results is closely related to the correlation between the satellite radar images used, and further that the study accuracy would improve with the inclusion of better correlation. In this way, representations of pre- and post-landslide terrains could be generated for use in numerical simulations. The InSAR method has particular significance for areas without terrain data prior to slope failure, and can provide basic data for landslide hazard assessments.

Detecting land subsidence near metro lines in the Baoshan district of Shanghai with multi-temporal interferometric synthetic aperture radar

Land subsidence is a major factor that affects metro line (ML) stability. In this study, an improved multi-temporal interferometric synthetic aperture radar (InSAR) (MTI) method to detect land subsidence near MLs is presented. In particular, our multi-temporal InSAR method provides surface subsidence measurements with high observation density. The MTI method tracks both point-like targets and distributed targets with temporal radar backscattering steadiness. First, subsidence rates at the point targets with low-amplitude dispersion index (ADI) values are extracted by applying a least-squared estimator on an optimized freely connected network. Second, to reduce error propagation, the pixels with high-ADI values are classified into several groups according to ADI intervals and processed using a Pearson correlation coefficient and hierarchical analysis strategy to obtain the distributed targets. Then, nonlinear subsidence components at all point-like and distributed targets are estimated using phase unwrapping and spatiotemporal filtering on the phase residuals. The proposed MTI method was applied to detect land subsidence near MLs of No. 1 and 3 in the Baoshan district of Shanghai using 18 TerraSAR-X images acquired between April 21, 2008 and October 30, 2010. The results show that the mean subsidence rates of the stations distributed along the two MLs are −12.9 and −14.0 mm/year. Furthermore, three subsidence funnels near the MLs are discovered through the hierarchical analysis. The testing results demonstrate the satisfactory capacity of the proposed MTI method in providing detailed subsidence information near MLs.

Bottom-fast ice delineation with PolSAR and InSAR techniques in the Mackenzie Delta region, Northwest Territories, Canada

Bottom-fast ice (BFI) refers to sea or lake ice that freezes to the sea or lake bed. The formation of BFI plays an important role in the Mackenzie Delta Region's seasonal environmental changes. This study involves examining the use of Synthetic Aperture Radar (SAR) images for delineating BFI from floating ice on a study site within the coastal region of the Mackenzie Delta. The ultimate aim is to establish robust BFI monitoring tools using SAR data processing techniques. BFI detection methodologies based on polarimetric SAR (PolSAR) image classification and interferometric SAR (InSAR) coherence segmentation have been examined using RADARSAT-2 data. Polarimetric analysis can use individual SAR images and is not susceptible to decorrelation factors such as weather events. By using these analysis techniques it is thus possible to delineate BFI extent throughout the winter. A limitation of these techniques is the sensitivity to the water and consequently the ice saline content. The polarimetric decompositions and classifications for delineation of BFI apply only to areas where the water has a low saline concentration. Conversely, InSAR methods for BFI delineation require interferometric datasets with high temporal coherence. The results of the interferometric datasets can eliminate false alarms in BFI maps caused by similar backscattered SAR signal from floating ice with varying degrees of salinity. The delineation results using both methods were analyzed and compared. It was found that though each method is able to detect and delineate BFI on its own, reliable and more accurate results occur when the two methods are combined, as the reliance on different phenomena allow for false alarm identification.

An Improved Multi-Temporal Insar Method for Increasing Spatial Resolution of Surface Deformation Measurements

Abstract. The multi-temporal interferometric synthetic aperture radar (InSAR) technology has proven very useful in extracting surface deformation with time series of SAR images over a study area. To increase spatial resolution of deformation information, this paper presents an improved multi-temporal InSAR (MTI) method by tracking both the point-like targets (PTs) and the distributed targets (DTs) with temporal steadiness of radar backscattering. The valid pixels corresponding to PTs and DTs are identified mainly by thresholding of the amplitude dispersion index (ADI) and the Pearson correlation coefficient (PCC). To efficiently reduce error propagation, a hierarchical analysis strategy is applied to extract deformation rates at the valid pixels. For the pixels with lower ADI values, the deformation rates are estimated on an optimized network by a least squared estimator and a region growing method. For the pixels with higher ADI values, they are classified into several groups by the ADI intervals, and the deformation rates are estimated through the multi-levels of processing. The nonlinear deformation values at all the valid pixels are estimated by spatiotemporally filtering and spatially integrating. The proposed MTI algorithm has been tested for subsidence detection over Tianjin in China using the 40 high resolution TerraSAR-X images acquired between 2009 and 2010, and validated by using the ground-based leveling measurements. The testing results indicate that the spatial resolution and coverage of subsidence data can be increased dramatically by the hierarchical analysis, and the accuracy in subsidence values derived from the MTI solution can reach up to a millimeter level.

Large-area landslide detection and monitoring with ALOS/PALSAR imagery data over Northern California and Southern Oregon, USA

Multi-temporal ALOS/PALSAR images are used to automatically investigate landslide activity over an area of ~200km by ~350km in northern California and southern Oregon. Interferometric synthetic aperture radar (InSAR) deformation images, InSAR coherence maps, SAR backscattering intensity images, and a DEM gradient map are combined to detect active landslides by setting individual thresholds. More than 50 active landslides covering a total of about 40km2 area are detected. Then the short baseline subsets (SBAS) InSAR method is applied to retrieve time-series deformation patterns of individual detected landslides. Down-slope landslide motions observed from adjacent satellite tracks with slightly different radar look angles are used to verify InSAR results and measurement accuracy. Comparison of the landslide motion with the precipitation record suggests that the landslide deformation correlates with the rainfall rate, with a lag time of around 1–2months between the precipitation peak and the maximum landslide displacement. The results will provide new insights into landslide mechanisms in the Pacific Northwest, and facilitate development of early warning systems for landslides under abnormal rainfall conditions. Additionally, this method will allow identification of active landslides in broad areas of the Pacific Northwest in an efficient and systematic manner, including remote and heavily vegetated areas difficult to inventory by traditional methods.

Global compilation of interferometric synthetic aperture radar earthquake source models: 2. Effects of 3-D Earth structure

[1] We carry out long-period surface wave centroid moment tensor (CMT) inversions using various global tomographic models and two different forward modeling techniques for 32 large earthquakes previously studied using interferometric synthetic aperture radar (InSAR) data. Since InSAR methods provide an alternative and independent way of locating and characterizing shallow continental earthquakes, comparisons of our source parameters with those from InSAR are a novel way to assess limitations in the InSAR models as well as the effects of inaccurate wave propagation formulations and/or 3-D Earth structure on earthquake source determinations. We show that comparing InSAR results with our seismic solutions is valuable to identify inaccuracies in the earthquake slip distribution retrieved using InSAR. Moreover, we find that using more accurate formulations, together with the best fitting Earth models, substantially reduces biases and differences between moment magnitude and fault strike determined using InSAR and seismic data. As expected for long-period surface wave source inversions for shallow earthquakes, the fault dip and rake angles are difficult to constrain, but we show that when using the best fitting Earth models, differences to InSAR estimates are reduced. Moreover, spurious deviations from a pure double-couple earthquake mechanism are on average smaller for the best fitting Earth models and the more accurate formulation of wave propagation. There are large differences between InSAR epicentral locations and those obtained in this study and, on average, no clear improvements to the Global CMT locations are achieved. This suggests that higher-resolution Earth models are necessary to further refine long-period CMT epicentral locations.

Digital elevation model generation using multibaseline advanced land observing satellite/phased array type L-band synthetic aperture radar imagery

The digital elevation model (DEM) forms fundamental topographical data for many scientific and engineering purposes including hydrology, geology, and civil applications. Using active and passive satellite remote sensing, it is an efficient and cost-effective approach to acquire up-to-date, accurate land cover and topographic information. One of the most important applications of interferometric synthetic aperture radar (SAR) technology is the determination of three-dimensional topographical information. Interferometric synthetic aperture radar (InSAR) DEM generation uses the measurement of the phase difference between two complex radar signals, or the difference in distance between satellite-borne SAR sensors and ground targets from two imaging passes. The parameters of the final DEM are related to the information contained within the master image. In addition, InSAR DEMs generated with different master images have varying grid sizes and location despite using the same coordinate systems. Consequently, the InSAR method can generate a multiplicity of DEMs using different combinations of the SAR image pairs. The authors propose a method that exploits the information contained in the area of overlap between different master and perpendicular baseline InSAR DEMs.

An examination of seasonal deformation at the Portuguese Bend landslide, southern California, using radar interferometry

The Portuguese Bend landslide, located on the Palos Verdes peninsula in southern California, is a slow‐moving landslide whose activity is closely tied to infiltration from rainfall. We use radar interferometry to constrain the seasonal kinematics of the landslide from 1995 to 2000. Traditional interferometric synthetic aperture radar methods estimate an average downslope displacement rate of 1.00 m/yr with an uncertainty range of 0.39–2.57 m/yr during the summer months. Interferograms show a consistent loss in phase coherence over the landslide for epochs greater than 6 months, especially in the winter. Interferograms become incoherent as a result of large displacement, and decorrelation is used to map the spatial extent of slide movement through time. The displacement rate increases sharply several weeks after the beginning of the rainy season as rainwater percolating into the slide elevates pore pressures. Phase coherence is lost when the slide velocity surpasses ∼2.6 m/yr for interferograms with durations of a few months. A physically based model based on rainfall‐driven landslide movement incorporates these observations to constrain hydraulic diffusivity to between 0.9 and 3.5 × 10−6 m2/yr.