The STUN algorithm for persistent scatterer interferometry

The Spatio-Temporal Unwrapping Network (STUN) is a new algorithm to estimate displacement and topography at Persistent Scatterer (PS) points using an interferometric single-master data stack. The STUN algorithm provides a robust method to explicitly unwrap the interferometric phase using the temporal and spatial correlations of the observed phase. Moreover, it uses alternative hypothesis tests and the integer Least-Squares estimator to optimally estimate the parameters. Key features are the ability (i) to model the displacement using a linear combination of basefunctions; (ii) to estimate the precision of each SLC image using a novel stochastic model; (iii) to obtain a description of the precision of the estimated displacements. This paper describes the STUN algorithm in detail, and demonstrates its practical application using data from a rural area nearby Marseille, France, which suffers from subsidence due to mining activities

Urban deformation monitoring in Bangkok metropolitan (Thailand) using permanent scatterer and differential interferometry techniques

Extensive ground water extraction has been identified as the principle cause of land subsidence in Bangkok and its vicinity. To mitigate major damages from large subsidence magnitudes the phenomenon must be well understood in this area. Up-to-date and reliable subsidence information is indispensable to develop this understanding. Conventionally, surface leveling has served as the primary method for measuring subsidence in Bangkok. But this is costly and time consuming. Differential SAR interferometry (DInSAR) can be an alternative means to obtain measurements of the surface displacement providing better resolution and comparable accuracy while being less time consuming. However, spatial and temporal decorrelation and atmospheric signal contributions in repeat-pass SAR interferometry often hamper the accurate measurement of surface displacements in SAR interferograms. The recently developed Permanent Scatterer (PS) technique invented by POLIMI researchers [1],[2],[3], overcomes these difficulties by interpreting time-series of interferometric phases at coherent point scatterers. In this study, we apply both DInSAR and PS techniques using two time-series of 17 and 11 ERS-SAR acquisitions for two partly overlapping image frames. This study is the first attempt to apply the PS technique to derive urban displacement information in Bangkok. We investigate the feasibility and reliability of using this technique with relatively few acquisitions and in a tropical location for deformation estimation. Using a linear deformation model and network algorithm, we estimate spatially varying displacement rates for the metropolitan area. Our first PS estimation results agree well with available ground leveling measurements

Development of a Scientific Permanent Scatterer System: Modifications for Mixed ERS/ENVISAT Time Series

The permanent scatterer technique invented at POLIMI has meanwhile developed into a remarkable operational method. It facilitates innovative data products such as urban subsidence maps or atmospheric delay measure-ments and permits new geophysical applications. The accuracy and validity of this techniques has been demonstrated in several projects at DLR. Due to the outstanding availability of data, time series of this technique have mainly been produced from data of the compatible satellite sensors ERS-1 and ERS-2. These time series can even span a continuous time range of about twelve years. This long-term observation enables the monitoring of displacements with millimetre accuracy and even facilitates the detection of seasonal periodic effects. The sensor ERS-1 made its last acquisition in 2000. The similarly constructed successor ERS-2 still moni-tors the Earth's surface even after nine years of operation. But recent acquisitions are unfortunately not suited for general interferometric applications. The reason is a heavily varying Doppler centroid frequency due to failures of gyros. The ERS-2 successor ENVISAT/ASAR is able to pursue the unique continuity in the monitoring of urban areas. But it operates with a slightly different radar frequency compared to the ERS sensors. Consequently the interferometric principle becomes more complicated and the processing has to be modified. We will present the required changes for the permanent scatterer cross interferometry on the developed scientific permanent scatterer system

Radar interferometry technique for urban subsidence monitoring: a case study in Bangkok and its vicinity

Temporal decorrelation and inhomogeneous atmospheric conditions in tropical climates restrict the successful application of classical differential interferometry for displacement detection. The recently developed ‘Permanent Scatterer’ interferometry can overcome these difficulties by analyzing phase histories of coherent point targets within a multi-interferogram framework. Temporal phase unwrapping is applied to obtain a displacement rate estimate based on a linear deformation model. Two tracks of 11 and 21 scenes of ERS-1/2 SAR data were used to derive an estimate of the displacement rate field in Bangkok by this approach. The results are compared with precise levelling measurements

The development of a scientific permanent scatterer system

DLR has achieved many years’ experience concerning space born radar interferometry. The interferometric system GENESIS was improved and extended for different projects, e.g. for differential interferometry (D-InSAR) and for highly specialised missions as the Shuttle Radar Topography Mission (SRTM). Recently, a POLIMI researcher team invented the permanent scatterer technique and demonstrated the capability to monitor displacements in urban areas with millimetre accuracy. This new processing allows innovative data products and permits completely new geophysical applications. Consequently, DLR's interferometry system is extended also for this new processing technique. The implemented processing system is currently at the stage of a scientific development and research platform. The development from a scientific via a semi-operational and finally into an operational system is ongoing. In this paper the developed permanent scatterer system is presented and examples are shown for processing products as displacement maps, evolution in time of single scatterers, atmospheric phase screen, digital elevation model (DEM) updates, super resolution images, calibrated radar scenes and radiometric improved images. Moreover, results from current projects are presented

Radarfernerundung zur Erfassung bergbaubedingter Senkungen

In dieser Studie werden bergbaubedingte Absenkungen der Erdoberfläche über einem Abbaufeld des Bergwerkes Prosper-Haniel (Ruhrgebiet) mit der Permanent Scatterer Technik als interferometrischer Methode der Radarfernerkundung untersucht. Der untertägige bergmännische Abbau verursacht großflächige Senkungsmulden an der Tagesoberfläche. Diese können mit Hilfe der Radarfernerkundung lokalisiert und analysiert werden. Als Methode wird dazu die differentielle Radar-Interferometrie (DInSAR) verwendet, die sich besonders zur Erfassung kleiner relativer Bewegungen eignet. Leider wird diese Auswertung der Radardaten im mitteleuropäischen Raum oft durch die Vegetation der Landoberfläche erschwert, die die feste Phasenbeziehung zeitlich voneinander getrennt aufgezeichneter Radarbilder beeinträchtigt. Je größer der zeitliche Abstand zweier Radaraufnahmen ist, desto schwieriger ist es typischerweise, interpretierbare Phasendifferenzen aus ihnen abzuleiten. Für die interferometrische Messung von Bodenbewegungen in möglichst langen Zeitreihen, steht neuerdings die sogenannte Permanent Scatterer Methode zur Verfügung. Dabei werden langzeitstabile Streuer mittels statistischer Methoden in den Radarbildern identifiziert, deren Bewegung anschließend gemessen wird. Der Beitrag gibt den aktuellen Stand der Analyse einer Zeitreihe von Radarszenen, sowie der darin beobachteten vertikalen Bewegungen über einem Abbaufeld des Bergwerkes Prosper-Haniel der Deutschen teinkohle AG wieder. In this study the the permanent scatterer technique is applied to interferometric satellite radar observations to analyze the surface subsidence induced by mining activities in the "Prosper-Haniel" hard coal mine (Ruhr region, Germany). Underground mining causes extensive subsidence at the earth's surface. This can be localized and analyzed using radar remote sensing. Differential radar interferometry (DInSAR) is well suited to detect small relative displacements in particular. Unfortunately, the interferometric analysis of radar data in central Europe is often hampered by extensively vegetated land surfaces that can destroy the deterministic phases differences in temporally separated images. Longer temporal separations between two radar acquisitions, typically reduce the ability to interpret the measured phase differences. The recently developed "Permanent Scatterer" technique now enables the construction of much longer time-series of displacement measurements than previously feasible. This method identifies scatterers in the radar images through statistical analysis that remain coherent over a long time and a wide range of viewing angles. Displacement measurements are then made at these points only. This paper presents preliminary results of an analysis of surface displacements above the "Prosper-Haniel" hard coal mine in Germany, using the Permanent Scatterer technique