Spaceborne SAR Interferometry Research Articles

Mechanics of the Kalabagh Fault, northwest Himalayan fold and thrust belt (convergence zone of India and Eurasia), using SAR interferometry and CFS

The Kalabagh strike–slip fault, which is characterized by right-lateral movement, is part of the northwestern Himalayan foreland fold and thrust belt in Pakistan. This structure marks the western and eastern terminations of the Salt Range and Surghar Ranges, respectively. No significant (>M6) earthquakes have been reported along the Kalabagh Fault in recent decades. Here, we take advantage of space-borne Sentinel-1A SAR interferometry to gain insight into the mechanics of faulting, aseismic creeping, and stress loading of the seismic cycle on the Kalabagh Fault spanning over approximately 7 years. In this study, we also removed the tropospheric effects using the Generic Atmospheric Correction Online Service data from the rate map. We further resolved the LOS deformation into both horizontal and vertical deformations. Our Bayesian inversion indicates that the fault experiences significant horizontal and vertical displacements. The fault’s southern and northern segments exhibit a creeping rate of approximately ∼4.2 ± 1.3 to 4.8 ± 1.6 mm/year, respectively, while the central section does not display any horizontal creeping. We found that the creeping is confined between 0 and ∼2.7 ± 1.1 km depth at the northern section and 0 and ∼3.9 ± 1.1 km on the southern section of the faults. Nevertheless, we found that the vertical creeping of ∼10 mm/year is confined between 0.5 and 6 km depth in the central segment of the fault. Moreover, our model does not resolve the interseismic slip at depth on the Kalabagh Fault. Our results affirm that Kalabagh Fault is creeping, and the internal deformation due to the presence of a thick salt layer over the decollement facilitates the creeping on this fault. In addition, Coulomb stress modeling depicts that the creeping on the Kalabagh Fault increases the Coulomb stress changes in the northern section of the KBF.

Automated estimation of forest height and underlying topography over a Brazilian tropical forest with single-baseline single-polarization TanDEM-X SAR interferometry

Forest height is an important variable for modeling terrestrial carbon storage and global carbon cycle dynamics. Spaceborne SAR Interferometry (InSAR) has the sensitivity to measure canopy height and the underlying topography. In this paper, we refine and automate an interferometric ground finding approach that exploits few-look (2- to 4-look) averaged interferograms and incorporates the use of a coherent electromagnetic simulator and field inventory data. Using the coherent electromagnetic simulator, an InSAR simulation based on field data is performed to study the true ground position as a function of the statistics of few-look InSAR phase heights from a model perspective. With this statistical model, both the underlying topography and the canopy height (mean and top canopy height) can be estimated. Using German Aerospace Center's (DLR) single-baseline single-polarization TanDEM-X InSAR data, we validate the approach over a Brazilian tropical forest (Tapajós National Forest) with both field inventory and lidar data. As validated against lidar data, the underlying topography is estimated to an accuracy of 3 m. At one hectare aggregated pixel size, InSAR phase-center height is best compared with the field/lidar mean canopy height with an accuracy of 2–3 m, while InSAR-inverted total height best characterizes the lidar top canopy height with an accuracy of 4–5 m. Given the global data availability of TanDEM-X and the future TanDEM-L, this approach has the potential for wall-to-wall mapping of forest height as well as underlying topography and also serves as a complementary tool to other existing InSAR, Polarimetric InSAR (PolInSAR) and SAR tomography (TomoSAR) methods when only single polarization and/or baseline data are available.

Introduction of Integrated Mining Impact Monitoring – i<sup>2</sup>Mon Development Project

Abstract. Monitoring of mining areas and associanted dam stability, has become increasingly important as the awareness of safety and environmental protection is rising. An appropriate monitoring scheme is necessitated to legally activate, reactivate, or terminate mining operations. The project Integrated Mining Impact Monitoring (i2Mon) aims to identify and analyze mining-induced impact, in particular its ground deformation. The monitoring system comprises terrestrial measurement and remote sensing: levelling, GPS, LiDAR scanning, UAV survey, and SAR interferometry. For interpretation and prediction, modelling will be used to simulate local displacements by different factors. The final goal is to launch an interactive GIS-based platform as an early warning and decision making system for mining industry. Currently, the project is proceeding from a preparatory phase. This paper focuses on spaceborne SAR interferometry, whereby we can cost-effectively monitor ground movement at millimeter level over a large area. We introduce the prototype of our InSAR monitoring system. The test result from Sentinel-1 images shows the surface movement during 2018 at a deactivating open-pit coal mine in Germany. We discuss the current status, ongoing works, planned test sites in Poland, and how we integrate data from different sensors and approaches.

Effects of tectonic structures and long-term seismicity on paraglacial giant slope deformations: Piz Dora (Switzerland)

The interplay of tectonic and climatic forcing in the development of Alpine deep-seated gravitational slope deformations (DSGSD) is still poorly understood. We investigate a giant DSGSD affecting the Piz Dora slope (Val Müstair, Switzerland) by geological, structural and geomorphological analyses, spaceborne SAR interferometry and numerical modelling.The DSGSD affects Permian terrigenous and volcanoclastic successions folded into a kilometre-scale asymmetric anticline during the Alpine orogenesis. The area is characterized by active tectonic uplift and widespread shallow seismicity with dominant dip-slip fault mechanisms, experienced fast deglaciation after the Last Glacial Maximum and periglacial conditions between the Lateglacial and Holocene. The slope is affected by morpho-structural features testifying to the deep-seated gravitational sliding of 1.85km3 of rock along a basal shear zone over 400m deep. Analysis of rock glaciers and DInSAR data show that the DSGSD was active in Lateglacial times and is presently deforming at rates ö 15mm/yr. Integrated kinematic analysis of field and radar data outlines a key control of the inherited fold structure on the DSGSD, with a transition from deep compound sliding to the West, controlled by massive conglomerates (Chazforà Formation), to shallower roto-translational sliding to the East, controlled by volcanoclastic foliated rocks (Ruina Formation). 2DFEM stress-strain numerical models, simulating the post-LGM slope evolution in static, pseudo-static and dynamic conditions allowed evaluating the contribution of long-term seismicity to DSGSD in a paraglacial setting. Dynamic modelling was performed starting from the characterization of a real earthquake, representative of the recent local seismotectonic activity, and scaled to obtain dynamic scenarios with different return periods. Results suggest that deglaciation-related perturbations promoted the inception of the DSGSD but not its complete development, that was likely stimulated by the long-term contribution of recurrent, small earthquakes. Our results suggest that inherited structures, active seismicity and deglaciation cooperate to promote paraglacial rock slope deformation in tectonically active Alpine settings.

Post-disaster assessment of 2017 catastrophic Xinmo landslide (China) by spaceborne SAR interferometry

This work was funded by Sichuan Science and Technology Plan Key Research and Development Program (Grant No. 2018SZ0339), National Natural Science Foundation of China (Grant No. 41801391), State Key Laboratory of Geodesy and Earth’s Dynamics Open fund (Grant No. SKLGED2018-5-3-E), The Funds for Creative Research Groups of China (Grant No. 41521002) and partially supported by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO), the State Agency of Research (AEI), and European Funds for Regional Development (FEDER), under project TIN2014-55413-C2-2-P and by the Spanish Ministry of Education, Culture and Sport, under project PRX17/00439. This work was also supported by the National Environment Research Council (NERC) through the Centre for the Observation and Modeling of Earthquakes, Volcanoes and Tectonics (COMET, ref.: come30001), the LiCS project (ref. NE/K010794/1), the ESA-MOST DRAGON-4 project (ref. 32244), and the Hunan Province Key Laboratory of Coal Resources Clean-Utilization and Mine Environment Protection, Hunan University of Science and Technology (Ref. E21608).

Generation of Large-Scale Moderate-Resolution Forest Height Mosaic With Spaceborne Repeat-Pass SAR Interferometry and Lidar

This paper provides an overview of the scattering model, inversion approach, and validation of the application results for creating large-scale moderate-resolution (hectare-level) mosaics of forest height through using spaceborne repeat-pass SAR interferometry and lidar. By incorporating several improvements to the forest height inversion and mosaicking approach, the height estimation accuracy along with the robustness of this approach have been considerably enhanced from its originally reported accuracy of RMSE of 3–4 m at a 20-hectare aggregated pixel size to RMSE of 3–4 m on the order of 3–6 hectares. Furthermore, practical data processing schemes are provided in detail. Extensive validation results are demonstrated which include: 1) a forest height mosaic (total area of 11.6 million hectares) is generated for the U.S. states of Maine and New Hampshire using Japanese Aerospace Exploration Agency’s (JAXA) ALOS-1 InSAR correlation data and a small airborne lidar strip (44 000 hectares); 2) the mosaic height estimates are further compared with the available airborne lidar data and field measurements over both flat and mountainous areas; and 3) feasibility of using modern repeat-pass InSAR satellites with short repeat interval is also examined by using JAXA’s ALOS-2 data. This simple and efficient approach is a potential observational prototype with much smaller error budget for the future spaceborne repeat-pass L-band InSAR systems with small spatial baseline and moderate/large temporal baseline (such as NISAR) in combination with lidar (such as GEDI) on the application of large-scale forest height/biomass mapping. It also serves as a complementary tool to the spaceborne single-pass InSAR systems using InSAR/PolInSAR methods when full-pol data are not available and/or when the underlying topography slope causes problems for these approaches.

Potential of Space-Borne PolInSAR for Forest Canopy Height Estimation Over India—A Case Study Using Fully Polarimetric L-, C-, and X-Band SAR Data

This paper aims to demonstrate the potential of space-borne datasets for forest height estimation over Indian tropical forests. Fully polarimetric space-borne SAR interferometry (PolInSAR) data is acquired at the L -, C -, and X -band frequencies. The X -band data are acquired in two modes—single pass and repeat pass. The datasets are compensated for decorrelation due to SNR and varying spatial baselines. The remaining major decorrelation is the volumetric decorrelation, which is modeled using random volume over ground model to estimate the PolInSAR height for all the three frequencies. The modified Three-stage inversion algorithm is utilized for forest stand height estimation. The effect of forest biomass on height inversion accuracy is assessed. Furthermore, a first-order estimate of the absolute temporal decorrelation is demonstrated for the repeat-pass space-borne PolInSAR datasets. Extensive field validation campaigns are carried out in the tropical forest ranges. The forest height is inverted using data at all the three frequencies and validated with field measured values. The zero-temporal baseline bistatic TerraSAR-X/TanDEM-X and the L -band ALOS-2/PALSAR-2 result in a good height inversion with ${\boldsymbol{r}^2}$ and RMSE of 0.77 and 1.86 m ( X -band) and 0.75 and 1.94 m ( L -band), respectively. Furthermore, a comparison of estimated height of ALOS-2/PALSAR-2, TerraSAR-X, and RadarSAT-2 has been done with respect to the estimated height of TerraSAR-X/TanDEM-X. It is observed that RMSE of height inversion with respect to TerraSAR-X/TanDEM-X height is found to be 5.4 m, 7.6 m, and 12.8 m for ALOS-2/PALSAR-2, RadarSAT-2, and TerraSAR-X, respectively.

Quantification of selective logging in tropical forest with spaceborne SAR interferometry

Tropical forest disturbance (such as selective logging and fire) along with deforestation have significant contributions to the carbon source due to land-use change and anthropogenic CO2 emissions, and thus envisioned by United Nation's REDD+ programme. In previous work, spaceborne single-pass InSAR phase-center height has been shown to have the capability of accurately monitoring the subtle height change due to forest growth and degradation (with meter or even sub-meter level RMSE about the regression curve fit to time). In this paper, a new approach using spaceborne SAR interferometry has been developed to detect and quantify selective logging events. In particular, a quantitative indicator of forest disturbance is first defined, namely disturbance index (DI; from 0 “no disturbance” to 1 “deforestation”). A numerical field data-based InSAR simulation is then performed to study the functional relationship between the field-measured DI and InSAR relative phase-center height change from a modeled perspective. A selective logging event (October 2015 through January 2016) over the Tapajos National Forest in Brazil is used for experimental validation. The InSAR-inverted DI estimates derived from DLR's TanDEM-X time-series data were compared with those measured from a field work over 32 quarter-hectare stands at Tapajos with relative RMSE of 30% for DI up to 0.3 and the disturbance epoch can be determined with an average accuracy of 13 days (constrained by the satellite repeat interval usually on the order of 2 weeks). As a comparison, the repeat-pass InSAR coherences from the concurrent JAXA's ALOS-2 data are shown to qualitatively correspond to the TanDEM-X results, confirming both the location and the epoch of the disturbance event. This new method is anticipated to contribute to the range of tools being developed for large-scale forest disturbance assessment and monitoring (for UN's REDD+ programme) through using spaceborne single-pass InSAR missions (e.g., DLR's TanDEM-X and in the future, TanDEM-L).

Land Subsidence in Chiayi, Taiwan, from Compaction Well, Leveling and ALOS/PALSAR: Aquaculture-Induced Relative Sea Level Rise

Chiayi County is located in the largest alluvial plain of Taiwan with extensive aquaculture and rice farming sustained by water extracted from groundwater wells. Chiayi is a typical aquaculture area affected by land subsidence, yet such lands worldwide combine to provide nearly 90% of global aquaculture products, greatly reducing oceanic overfishing problems. This study uses precision leveling, multi-layer compaction monitoring well (MLCW) and spaceborne SAR interferometry (InSAR) to examine the cause and effect of land subsidence in Chiayi associated with groundwater extractions and changes. Heights at benchmarks in a leveling network are measured annually and soil compactions at 24–26 layers up to 300-m depths at 7 MLCWs are collected at one-month intervals. Over 2007–2011, 15 ALOS/PALSAR images are processed by the method of TCPInSAR to produce subsidence rates. All sensors show that land subsidence occur in most parts of Chiayi, with rates reaching 4.5 cm/year around its coast, a result of groundwater pumping from shallow to deep aquifers. MLCWs detect mm-accuracy seasonal soil compactions coinciding with groundwater level fluctuations and causing dynamic compactions. Compactions near Taiwan High Speed Rail may reduce the strength of the rail’s supporting columns to degrade its safety. The SAR images yield subsidence rates consistent with those from leveling and compaction wells after corrections for systematic errors by the leveling result. Subsidence in Chiayi’s coastal area leads to relative sea level rises at rates up to 15 times larger than the global eustatic sea level rising rate, a risk typical for world’s aquaculture-rich regions. At the fish pond-covered Budai Township, InSAR identifies subsidence spots not detected by leveling, providing crucial geo-information for a sustainable land management for aquaculture industry.

Locating and defining underground goaf caused by coal mining from space-borne SAR interferometry

It is crucial to locate underground goafs (i.e., mined-out areas) resulting from coal mining and define their spatial dimensions for effectively controlling the induced damages and geohazards. Traditional geophysical techniques for locating and defining underground goafs, however, are ground-based, labour-consuming and costly. This paper presents a novel space-based method for locating and defining the underground goaf caused by coal extraction using Interferometric Synthetic Aperture Radar (InSAR) techniques. As the coal mining-induced goaf is often a cuboid-shaped void and eight critical geometric parameters (i.e., length, width, height, inclined angle, azimuth angle, mining depth, and two central geodetic coordinates) are capable of locating and defining this underground space, the proposed method reduces to determine the eight geometric parameters from InSAR observations. Therefore, it first applies the Probability Integral Method (PIM), a widely used model for mining-induced deformation prediction, to construct a functional relationship between the eight geometric parameters and the InSAR-derived surface deformation. Next, the method estimates these geometric parameters from the InSAR-derived deformation observations using a hybrid simulated annealing and genetic algorithm. Finally, the proposed method was tested with both simulated and two real data sets. The results demonstrate that the estimated geometric parameters of the goafs are accurate and compatible overall, with averaged relative errors of approximately 2.1% and 8.1% being observed for the simulated and the real data experiments, respectively. Owing to the advantages of the InSAR observations, the proposed method provides a non-contact, convenient and practical method for economically locating and defining underground goafs in a large spatial area from space.

An innovative procedure for monitoring the change in soil seismic response by InSAR data: application to the Mexico City subsidence

We developed an empirical procedure to evaluate the effect of the ground subsidence on the spatial and temporal seismic response of soils. The proposed method exploits the capabilities of the spaceborne SAR Interferometry technique to detect and map the ground subsidence with unprecedented spatial and temporal coverage. The information provided by satellites is combined with a-priori geological/geotechnical information to assess the soil compaction and the shortening of the soil vibration periods. The procedure was applied to estimate the shortening of the soil resonant period of Mexico City between 2005 and 2013. The results show that in approximately nine years the ground surface has subsided by approximately 0.5⿿3.5m and the soil resonant period has decreased by approximately 0.1⿿0.4s. The obtained results, validated with field measurements, highlight the effectiveness of the proposed procedure for the continuous monitoring of the soil resonant periods. The estimated change in resonant period on Mexico City has a great impact on the response spectra used for design, it is then necessary to update the map of the soil resonant period in order to account for the change of dynamic properties of soils caused by subsidence.

Measuring ground subsidence in Hanoi city by radar interferometry

The rapidly developing urbanization since the last decade of the 20th century leads to the strong groundwater extraction, resulting in the subsidence phenomena in the Hanoi, Vietnam. Recent advances in the multi-temporal spaceborne SAR interferometry, especially with Persistent Scatters Interferometry (PSI) approach, is the robust remote sensing technique for measuring ground subsidence in large scale with millimetric accuracy. This work has presented an advanced PSI analysis, to provide unprecedented spatial extent and continuous temporal coverage of the subsidence in Hanoi City. The correlation between the reference leveling velocity and the estimated PSI result is R2 = 0.86, and the root mean square error is 4.0 (mm/year), confirming their good agreement. The study shows that subsidence is most severe in the Haihung silt loam areas in the south of the city. The groundwater extraction resulting from urbanization and urban growth is mainly responsible for the subsidence.

The Space-Borne SBAS-DInSAR Technique as a Supporting Tool for Sustainable Urban Policies: The Case of Istanbul Megacity, Turkey

In today’s urbanizing world, home of 28 megacities, there is a growing need for tools to assess urban policies and support the design and implementation of effective development strategies. Unsustainable practices of urbanization bring major implications for land and environment, and cause a dramatic increase of urban vulnerability to natural hazards. In Istanbul megacity, disaster risk reduction represents a challenging issue for urban managers. In this paper, we show the relevance of the space-borne Differential SAR Interferometry (DInSAR) technique as a tool for supporting risk management, and thus contributing to achieve the urban sustainability. To this aim, we use a dataset of high resolution SAR images collected by the TerraSAR-X satellite that have been processed through the advanced (multi-temporal) Small BAseline Subset (SBAS)—DInSAR technique, thus producing spatially-dense deformation velocity maps and associated time-series. Results allow to depict an up-to-date picture of surface deformations occurring in Istanbul, and thus to identify urban areas subject to potential risk. The joint analysis of remotely sensed measurements and ancillary data (geological and urban development information) provides an opportunity for city planners and land professionals to discuss on the mutual relationship between urban development policies and natural/man-made hazards.

Mapping Ground Subsidence Phenomena in Ho Chi Minh City through the Radar Interferometry Technique Using ALOS PALSAR Data

The rapidly developing urbanization since the last decade of the 20th century has led to extensive groundwater extraction, resulting in subsidence in Ho Chi Minh City, Vietnam. Recent advances in multi-temporal spaceborne SAR interferometry, especially with a persistent scatters interferometry (PSI) approach, has made this a robust remote sensing technique for measuring large-scale ground subsidence with millimetric accuracy. This work has presented an advanced PSI analysis, to provide an unprecedented spatial extent and continuous temporal coverage of the subsidence in Ho Chi Minh City from 2006 to 2010. The study shows that subsidence is most severe in the Holocene silt loam areas along the Sai Gon River and in the southwest of the city. The groundwater extraction resulting from urbanization and urban growth is mainly responsible for the subsidence. Subsidence in turn leads to more flooding and water nuisance. The correlation between the reference leveling velocity and the estimated PSI result is R2 = 0.88, and the root mean square error is 4.3 (mm/year), confirming their good agreement. From 2006 to 2010, the estimation of the average subsidence rate is -8.0 mm/year, with the maximum value up to -70 mm/year. After four years, in regions along Sai Gon River and in the southwest of the city, the land has sunk up to -12 cm. If not addressed, subsidence leads to the increase of inundation, both in frequency and spatial extent. Finally, regarding climate change, the effects of subsidence should be considered as appreciably greater than those resulting from rising sea level. It is essential to consider these two factors, because the city is inhabited by more than 7.5 million people, where subsidence directly impacts urban structures and infrastructure.

Analysis of building deformation in landslide area using multisensor PSInSAR™ technique

Buildings are sensitive to movements caused by ground deformation. The mapping both of spatial and temporal distribution, and of the degree of building damages represents a useful tool in order to understand the landslide evolution, magnitude and stress distribution. The high spatial resolution of space-borne SAR interferometry can be used to monitor displacements related to building deformations. In particular, PSInSAR technique is used to map and monitor ground deformation with millimeter accuracy. The usefulness of the above mentioned methods was evaluated in San Fratello municipality (Sicily, Italy), which was historically affected by landslides: the most recent one occurred on 14th February 2010. PSInSAR data collected by ERS 1/2, ENVISAT, RADARSAT-1 were used to study the building deformation velocities before the 2010 landslide. The X-band sensors COSMO-SkyMed and TerraSAR-X were used in order to monitor the building deformation after this event. During 2013, after accurate field inspection on buildings and structures, damage assessment map of San Fratello were created and then compared to the building deformation velocity maps. The most interesting results were obtained by the comparison between the building deformation velocity map obtained through COSMO-SkyMed and the damage assessment map. This approach can be profitably used by local and Civil Protection Authorities to manage the post-event phase and evaluate the residual risks.

Multitemporal landslides inventory map updating using spaceborne SAR analysis

Deep seated gravitational slope deformation and slow moving landslides on large areas were analyzed by spaceborne SAR interferometry: a test site in the Italian Alps of about 300km2 was selected for updating pre-existing landslide inventory maps based on the advanced interferometric processing technique (A-DInSAR).SAR images from ERS-1/2 satellites (1995–2000) and from Envisat satellite (2002–2009) have been used, allowing the deferred-time analysis of past movements and the record of recent slope movements. In the multi-temporal updated landslide inventory database, the characteristics of the landslides were highlighted: geometry, state of activity, typology, monitoring systems, interventions, source of information and the updating time and actions. Furthermore, for each landslide area, the occurrence of persistent scatterers points and the statistical description of their velocities were reported. This methodology may allow the systematic updating of landslides inventory maps keeping all information on each landslide, becoming the basic tool for the realization and updating of thematic maps such as the landslide susceptibility map.

Surface displacement estimation using space-borne SAR interferometry in a small portion along Himalayan Frontal Fault

Earthquake is one of the most destructive natural hazards which pose a real threat to India with nearly 59% of its geographical area vulnerable to seismic disturbance of varying intensities including the capital city of the country. India has experienced several major earthquakes mainly in Himalayan region and is also considered as one of the most earthquake prone regions in the world. Therefore, during past few decades, the Himalayan region has been studied extensively in terms of present ongoing displacements. It can be believed that a better estimate of the current Himalayan convergence rate and possible rupture can improve seismic hazard evaluations. Moreover, an improved convergence rate is also necessary to estimate if any slip deficit is available to drive future earthquakes in this region. In recent years, SAR interferometry has been successfully used for generating large scale surface displacement maps in radar look direction on a dense grid and with a centimeter to millimeter accuracy. In this context, the usefulness of SAR interferometry technique and its variations for estimation of displacements has been studied and presented in this paper. To study the displacement both conventional and multi-temporal Differential SAR interferometry has been used. In order to get the 3-D surface displacement, interferogram from both ascending and descending track can be used. However, due to the unavailability of ascending track data, a well-known mathematical model also has been used. Overall average displacement rates in the present study are found to be relatively lower as compared to the reported convergence rates. From geophysical point of view, the results presented in this paper for a small area are quite promising. Several explanations have also been presented in this paper to support the results. The reported low convergence rate may be due to the occurrence of silent/quite earthquakes, aseismic slip, differential movement of Delhi Hardwar ridge, etc. Therefore, in view of the contemporary seismicity and conspicuous displacements, a study of long-term observations of this surface movement has been recommended in future.

Advances in space-borne SAR interferometry and its application to ground deformation monitoring

The development of Differential Synthetic Aperture Radar Interferometry (D-InSAR), in terms of its evolution from classic to advanced forms, such as Least-Squares approach, Permanent Scatterer Interferometry, Small Baseline Subset, and Coherent Pixel Technique, is reviewed, describing concisely the main principles of each method and highlighting the difference and relationship between them. Applications of InSAR technology in China were then introduced, together with the obstacles to overcome and feasible strategies, such as integrating MERIS/MODIS data to compensate for the atmospheric effect and GPS, and multi-platform SAR data to make InSAR technique practical and operational under various conditions. The latest developments were then analyzed along with high-quality SAR data, available thanks to the newly launched high-tech satellites, TerraSAR-X, and Cosmo Sky-med, and conclusions were drawn about the main limitations of the technique.

DEM generation using ERS–ENVISAT interferometry

Space-borne SAR interferometry is one possible method for the generation of digital elevation models (DEMs). The sensitivity of this technique depends strongly on system parameters as the time interval between the observations used and the spatial baseline. Longer time intervals are less suited because of temporal decorrelation of the signal. Longer spatial baselines result in an increased height sensitivity. ERS-2 and ENVISAT ASAR operate in identical orbits at slightly different sensor frequencies with ASAR preceding ERS-2 by 28 min. This configuration offers a unique opportunity to study and apply ERS–ENVISAT interferometry. ERS-2–ENVISAT ASAR IS2 VV-polarization interferograms are characterized by a short 28 min repeat-pass interval and a long 1.5–2.5 km baseline. Given the long baseline and short time interval ERS–ENVISAT interferometry has a good potential for the generation of precise DEMs in relatively flat areas. The idea to use ERS–ENVISAT interferometry for DEM generation is not new, nevertheless, very few adequate data sets were identified and analyzed in the past. Now, thanks to a recent dedicated ERS-2–ENVISAT Tandem mission of ESA many well suited data sets became available. In this paper the ERS–ENVISAT interferometry methodology is described, its feasibility is demonstrated by presenting ERS–ENVISAT interferometry DEMs over several sites, and its potential is assessed.

Identifying urban SAR Permanent Scatterers for motion interpretation and multi-track data fusion

The Permanent Scatterers (PS) technique is a processing tool in the field of space-borne SAR interferometry to detect terrain deformations with millimetre accuracy. Such an accuracy is achieved in correspondence of coherent targets, the so-called Permanent Scatterers. Recently the PS physical nature has been subject of study and a set of main target typologies (dihedrals, trihedrals, poles, roofs, metal gratings) has been found being recognizable by means of features extracted from the radar data. In this work we analyse the main applications that derive from the recognition of the PS scattering type: the interpretation of the deformation measurements, the increase of the temporal sampling rate (combining data acquired from parallel orbits by means of dihedrals), the increase of the number of measurement points (combining data acquired from ascending and descending passes by means of poles).