High-resolution deformation measurement using "Persistent Scatterer Interferometry"

Persistent Scatterer Interferometry (PSI) is a group of advanced differential interferometric SAR techniques that are used to measure and monitor terrain deformation. Different PSI techniques have been proposed in the last two decades. In this thesis, the two PSI chains implemented and used at the Geomatics division of CTTC are described: the local area PSI and the PSIG chains. The first part of the thesis is devoted to the local area PSI chain, used to analyse the deformations over small areas. The chain includes a linear deformation model to directly deal with interferometric wrapped phases. Moreover, it does not directly involve the estimation of the APS, thus simplifying the procedure and its computational cost. The chain has been tested using different types of SAR data. The availability of high resolution X-band SAR data has led to an improvement of the PSI results with respect to C-band data. The higher image resolution and phase quality implies an increase of the PS density, an improvement in the estimation precision of the residual topographic error and a higher sensibility to very small deformations, including the displacements caused by thermal dilation. An extension of the classical PSI linear deformation model has been proposed, to account for the thermal dilation effects. This allows obtaining a new PSI outcome, the thermal dilation parameter, which opens new interesting applications since it provides information on the physical properties of single objects, i.e. the coefficient of thermal expansion, and the static structures of the same objects. The second part of the thesis describes the PSIG chain, whose aim was to extend the interferometric processing to wider areas. The ability to cover wide areas is essential to obtain a unique and consistent deformation monitoring for the available SAR image full scenes, i.e. typically 30 by 50 km for TerraSAR-X, 40 by 40 km for CosmoSkyMed and 100 by 100 km for ASAR ENVISAT and ERS. This is particularly important for the forthcoming C-band Sentinel SAR data that will cover 250 by 250 km with a single image scene. The key steps of the PSIG procedure include a new selection of candidate PSs based on a phase similitude criteria and a 2+1D phase unwrapping algorithm. The procedure offers different tools to control the quality of the processing steps. It has been successfully tested over urban, rural and vegetated areas using X-band PSI data. The performance of the PSIG chain is illustrated and discussed in detail, analysing the procedure step by step.Persistent Scatterer Interferometry (PSI) és un grup de tècniques avançades d'interferometria diferencial SAR que s'utilitzen per mesurar i monitoritzar deformacions del terreny. Durant les últimes dues dècades s’han proposat diverses tècniques PSI. En aquesta tesi es descriuen les dues cadenes PSI implementades i utilitzades en la divisió de Geomàtica del CTTC: la cadena PSI d’àrea local i la cadena PSIG. La primera part de la tesi està dedicada a la cadena PSI d’àrea local, que s'utilitza per analitzar deformacions en zones d’extensió limitada. La cadena inclou un model de deformació lineal per tractar directament amb les fases interferomètriques wrapped. En canvi, no estima directament la component atmosfèrica, cosa que simplifica el procediment i el seu cost computacional. La cadena s’ha provat sobre diferents tipus de dades SAR. La disponibilitat de dades SAR d’alta resolució en banda X ha donat lloc a una millora dels resultats del PSI respecte a les dades en banda C. La resolució més gran de la imatge i la qualitat de la fase impliquen un augment de la densitat de PS, una millora en la precisió de l'estimació de l'error topogràfic residual i una sensibilitat més alta a deformacions subtils, incloent-hi els desplaçaments causats per la dilatació tèrmica. Per tenir en compte els efectes de la dilatació tèrmica, s'ha proposat una extensió del model PSI clàssic que ens permet obtenir un nou producte PSI: el paràmetre de dilatació tèrmica. Aquest paràmetre obre noves aplicacions interessants: proporciona informació relacionada amb les propietats físiques dels objectes mesurats –com el coeficient d'expansió tèrmica– i amb la seva pròpia estructura estàtica. La segona part de la tesi descriu la cadena PSIG, l'objectiu de la qual és estendre el processament interferomètric a àrees més extenses. La capacitat de cobrir àrees grans és fonamental per obtenir un únic mapa global de deformacions que sigui consistent i cobreixi l’extensió sencera de les imatges SAR disponibles, de 30 km per 50 km per TerraSAR-X, de 40 km per 40 km per CosmoSkyMed i de 100 km per 100 km per ASAR-ENVISAT i ERS. Això és particularment important tenint en compte la propera disponibilitat de les dades del satèl•lit Sentinel, que opera en banda C i cobrirà 250 km per 250 km amb una sola imatge. Els passos clau del procediment PSIG són una nova selecció de PS candidats en base a un criteri de similitud de fase i un algoritme de 2+1D phase unwrapping. El procediment ofereix diferents eines per controlar la qualitat dels diferents passos del processament. La cadena PSIG s’ha utilitzat amb èxit en àrees urbanes, rurals i amb vegetació utilitzant dades PSI en banda X. El funcionament de la cadena PSIG s'il•lustra i es descriu en detall, analitzant el procediment pas a pas

Elevation and Deformation Extraction from TomoSAR

3D SAR tomography (TomoSAR) and 4D SAR differential tomography (Diff-TomoSAR) exploit multi-baseline SAR data stacks to provide an essential innovation of SAR Interferometry for many applications, sensing complex scenes with multiple scatterers mapped into the same SAR pixel cell. However, these are still influenced by DEM uncertainty, temporal decorrelation, orbital, tropospheric and ionospheric phase distortion and height blurring. In this thesis, these techniques are explored. As part of this exploration, the systematic procedures for DEM generation, DEM quality assessment, DEM quality improvement and DEM applications are first studied. Besides, this thesis focuses on the whole cycle of systematic methods for 3D & 4D TomoSAR imaging for height and deformation retrieval, from the problem formation phase, through the development of methods to testing on real SAR data. After DEM generation introduction from spaceborne bistatic InSAR (TanDEM-X) and airborne photogrammetry (Bluesky), a new DEM co-registration method with line feature validation (river network line, ridgeline, valley line, crater boundary feature and so on) is developed and demonstrated to assist the study of a wide area DEM data quality. This DEM co-registration method aligns two DEMs irrespective of the linear distortion model, which improves the quality of DEM vertical comparison accuracy significantly and is suitable and helpful for DEM quality assessment. A systematic TomoSAR algorithm and method have been established, tested, analysed and demonstrated for various applications (urban buildings, bridges, dams) to achieve better 3D & 4D tomographic SAR imaging results. These include applying Cosmo-Skymed X band single-polarisation data over the Zipingpu dam, Dujiangyan, Sichuan, China, to map topography; and using ALOS L band data in the San Francisco Bay region to map urban building and bridge. A new ionospheric correction method based on the tile method employing IGS TEC data, a split-spectrum and an ionospheric model via least squares are developed to correct ionospheric distortion to improve the accuracy of 3D & 4D tomographic SAR imaging. Meanwhile, a pixel by pixel orbit baseline estimation method is developed to address the research gaps of baseline estimation for 3D & 4D spaceborne SAR tomography imaging. Moreover, a SAR tomography imaging algorithm and a differential tomography four-dimensional SAR imaging algorithm based on compressive sensing, SAR interferometry phase (InSAR) calibration reference to DEM with DEM error correction, a new phase error calibration and compensation algorithm, based on PS, SVD, PGA, weighted least squares and minimum entropy, are developed to obtain accurate 3D & 4D tomographic SAR imaging results. The new baseline estimation method and consequent TomoSAR processing results showed that an accurate baseline estimation is essential to build up the TomoSAR model. After baseline estimation, phase calibration experiments (via FFT and Capon method) indicate that a phase calibration step is indispensable for TomoSAR imaging, which eventually influences the inversion results. A super-resolution reconstruction CS based study demonstrates X band data with the CS method does not fit for forest reconstruction but works for reconstruction of large civil engineering structures such as dams and urban buildings. Meanwhile, the L band data with FFT, Capon and the CS method are shown to work for the reconstruction of large manmade structures (such as bridges) and urban buildings

Active and Passive Multi-Sensor Radar Imaging Techniques Exploiting Spatial Diversity

The work here presented reports several innovative SAR and ISAR radar imaging techniques exploiting the spatial diversity offered by multi-sensor systems in order to improve the performance with respect to the conventional, single channel cases. Both the cases of dedicated transmitters and exploitation of opportunity transmitters are considered

Active and Passive Multi-Sensor Radar Imaging Techniques Exploiting Spatial Diversity

The work here presented reports several innovative SAR and ISAR radar imaging techniques exploiting the spatial diversity offered by multi-sensor systems in order to improve the performance with respect to the conventional, single channel cases. Both the cases of dedicated transmitters and exploitation of opportunity transmitters are considered

Geodetic monitoring of complex shaped infrastructures using Ground-Based InSAR

In the context of climate change, alternatives to fossil energies need to be used as much as possible to produce electricity. Hydroelectric power generation through the utilisation of dams stands out as an exemplar of highly effective methodologies in this endeavour. Various monitoring sensors can be installed with different characteristics w.r.t. spatial resolution, temporal resolution and accuracy to assess their safe usage. Among the array of techniques available, it is noteworthy that ground-based synthetic aperture radar (GB-SAR) has not yet been widely adopted for this purpose. Despite its remarkable equilibrium between the aforementioned attributes, its sensitivity to atmospheric disruptions, specific acquisition geometry, and the requisite for phase unwrapping collectively contribute to constraining its usage. Several processing strategies are developed in this thesis to capitalise on all the opportunities of GB-SAR systems, such as continuous, flexible and autonomous observation combined with high resolutions and accuracy. The first challenge that needs to be solved is to accurately localise and estimate the azimuth of the GB-SAR to improve the geocoding of the image in the subsequent step. A ray tracing algorithm and tomographic techniques are used to recover these external parameters of the sensors. The introduction of corner reflectors for validation purposes confirms a significant error reduction. However, for the subsequent geocoding, challenges persist in scenarios involving vertical structures due to foreshortening and layover, which notably compromise the geocoding quality of the observed points. These issues arise when multiple points at varying elevations are encapsulated within a singular resolution cell, posing difficulties in pinpointing the precise location of the scattering point responsible for signal return. To surmount these hurdles, a Bayesian approach grounded in intensity models is formulated, offering a tool to enhance the accuracy of the geocoding process. The validation is assessed on a dam in the black forest in Germany, characterised by a very specific structure. The second part of this thesis is focused on the feasibility of using GB-SAR systems for long-term geodetic monitoring of large structures. A first assessment is made by testing large temporal baselines between acquisitions for epoch-wise monitoring. Due to large displacements, the phase unwrapping can not recover all the information. An improvement is made by adapting the geometry of the signal processing with the principal component analysis. The main case study consists of several campaigns from different stations at Enguri Dam in Georgia. The consistency of the estimated displacement map is assessed by comparing it to a numerical model calibrated on the plumblines data. It exhibits a strong agreement between the two results and comforts the usage of GB-SAR for epoch-wise monitoring, as it can measure several thousand points on the dam. It also exhibits the possibility of detecting local anomalies in the numerical model. Finally, the instrument has been installed for continuous monitoring for over two years at Enguri Dam. An adequate flowchart is developed to eliminate the drift happening with classical interferometric algorithms to achieve the accuracy required for geodetic monitoring. The analysis of the obtained time series confirms a very plausible result with classical parametric models of dam deformations. Moreover, the results of this processing strategy are also confronted with the numerical model and demonstrate a high consistency. The final comforting result is the comparison of the GB-SAR time series with the output from four GNSS stations installed on the dam crest. The developed algorithms and methods increase the capabilities of the GB-SAR for dam monitoring in different configurations. It can be a valuable and precious supplement to other classical sensors for long-term geodetic observation purposes as well as short-term monitoring in cases of particular dam operations

Using digital television signals for radar imaging

This thesis presents the first systematic theoretical and experimental study of passive bistatic Synthetic Aperture Radar (SAR) imaging utilising Digital Television Broadcasting - Terrestrial (DVB-T) as an illuminator of opportunity. It presents the theoretical background for radar, SAR, and DVB-T transmissions, and studies the waveform on the basis of its ambiguity function. It considers the theoretical constraints of DVB-T SAR, including the impact of multiple transmitters and the properties of the DVB-T signal on image formation. It tracks the development and evolution of a receiver system and image formation algorithm, which is then validated through a series of ground-based and airborne experimental campaigns. From these campaigns, a catalogue of images are produced and analysed in order to establish the informational potential of DVB-T SAR imagery in both quasi-monostatic and bistatic environments. Specifically, the quality of images formed from a range of bistatic angles from 4 to 140 degrees is considered

Middle Atmosphere Program. Handbook for MAP, volume 28

Extended abstracts from the fourth workshop on the technical and scientific aspects of MST (mesosphere stratosphere troposphere) radar are presented. Individual sessions addressed the following topics: meteorological applications of MST and ST radars, networks, and campaigns; dynamics of the equatorial middle atmosphere; interpretation of radar returns from clear air; techniques for studying gravity waves and turbulence; intercomparison and calibration of wind and wave measurements at various frequencies; progress in existing and planned MST and ST radars; hardware design for MST and ST radars and boundary layer/lower troposphere profilers; signal processing; and data management