A persistent scatterer experiment using corner reflectors has been set up to validate the quality of InSAR Envisat/ERS-2 phase observations. The validation is performed by means of independent precise leveling observations of corner reflector motion in time, and comparison with respect to InSAR observables. The estimated precision of the InSAR double-differenced phase measurements is 2.8mm (vertical) for "zero-gyro" ERS-2 data and 1.6mm for Envisat. An analysis of an integration of corner reflectors and neighboring "natural" persistent scatterers is also presented. @en

The start of hydrocarbon production in the 1960s in the northeastern part of the Netherlands has resulted in subsidence of the ground level, which has been estimated from periodic leveling campaigns. Although leveling is a precise and reliable technique for subsidence monitoring, it is labor intensive, expensive and poses a safety risk since measurements are taken along roads. Hence, the application of satellite radar interferometry (InSAR) is investigated for subsidence monitoring, coupled with the potential improvement of reservoir behavior monitoring due to the InSAR observation frequency. The main focus lies on the Groningen gas field, which has a diameter of ∼30 kilometers, at ∼3 kilometers below surface. Complicating factors for the application of InSAR for subsidence monitoring in the Groningen area are surface changes in time due to its agricultural character (temporal decorrelation), atmospheric disturbances, and the low subsidence rates (< 1 cm/year) over a large spatial extent. Hence, the applicability of Persistent Scatterer InSAR (PSI) is investigated. PSI utilizes objects with a coherent phase behavior in time for the estimation of deformation and other phase contributions. Since the subsidence monitoring period exceeds the lifetime of a satellite (5–10 years), multiple sensors are required: ERS-1, ERS-2 and Envisat phase observations have been used.@en

In the PSIC4 experiment, eight different processing approaches for time series analysis of InSAR data were applied to a data set containing an unknown deformation signal. Results of the experiment showed different spatial point density for different processing approaches. The results of most of the groups that participated in the project suffer from a low spatial density of persistent scatterers in deforming areas. This lack of PS points in the area of interest raises the hypothesis of type-I errors (falsely rejected PS) due to imperfections in the mathematical model of PS processing. We investigate the contribution of three different sources of type-I errors: atmospheric phase screen (APS) and orbital errors, non-linear deformation mechanisms, and azimuthal sub-pixel position of the scatterers. We investigate these type-I errors and present significant improvements in their identification by optimization of the mathematical model, leading to an improved density of persistent scatterers. @en

InSAR data acquired from independent overlapping tracks can be exploited for a reliability assessment of the Persistent Scatterer InSAR (PS-InSAR) technique. This is obtained by means of the datum connection of multiple tracks, simultaneously evaluating the misclosures between multi-track PS-InSAR estimates. Due to a different viewing geometry, many of the detected PS will physically not be the same. However, their estimates may still refer to the same deformation signal. The existence of independent observations of the same deformation signal provides a powerful tool to increase the redundancy and evaluate the reliability. The datum connection can be subdivided in two steps. The first step consists of the conversion of PS locations to a common datum. Secondly, the PS-InSAR parameter estimates (velocities, displacements, heights) are connected. In stead of the conventional approach of separately geocoding each track, we propose the use of a common radar datum defined by the acquisition geometry of the 'master track'. Multi-track datum connection has been applied in the Groningen region, the Netherlands, which is affected by subsidence due to gas extraction with displacement rates up to 7 mm/year. The main reservoir is (partly) visible in 6 independent overlapping ERS tracks from 1992 (ascending and descending). Datum connection resulted in a consistent set of PS-InSAR deformation estimates. Additionally, the deformation signal was decomposed in horizontal and vertical movements, utilizing the different viewing geometries of the tracks. ©2007 IEEE. @en

InSAR data acquired from independent overlapping tracks can be exploited for a reliability assessment of the Persistent Scatterer InSAR (PS-InSAR) technique. Here we present a mathematical framework for the datum connection of multiple tracks, simultaneously evaluating the precision and reliability of PS-InSAR estimates. This datum connection can be subdivided in two steps. Firstly, the PS locations are converted to a common radar coordinate system: the geometry of the so-called 'master track'. The second step consists of the connection of the PS-InSAR parameter estimates (velocities, displacements, heights). Since each track has its own reference PS, the transformation is parameterized as a translation, which can be optionally extended with a trend in range and azimuth direction due to unmodeled residual effects. Multi-track datum connection has been applied in the Groningen region, the Netherlands, which is affected by subsidence due to gas extraction with displacement rates up to 7 mm/year. The main reservoir is (partly) visible in 6 independent overlapping ERS tracks (ascending and descending). Utilizing the different viewing geometries, the connected PSInSAR estimates could be further decomposed into horizontal and vertical displacement rates. @en

SAR amplitude calibration is performed prior to the selection of potential Persistent Scatterers (PS) to avoid amplitude variations due to sensor characteristics and viewing geometry. As only the interferometric phases of a small percentage of the radar pixels in an image is used in the PS-InSAR analysis, it is investigated if this time and storage space consuming step can be omitted. We present an integrated method which does not perform amplitude calibration explicitly, but integrates it into the PS point selection procedure for validation purposes by evaluating the hypothesis that a point would have been selected if all images were calibrated beforehand. Its performance assessment is based on coherent phase behavior of the selected potential PS and indicates that empirical calibration validation is an alternative for calibrating full images based on physical sensor parameters.@en

In radar images, point scatterers provide reflections that can often be attributed to a single physical object, usually smaller than the resolution cell size. Stable point scatterers with high backscatter coefficients through time (mainly 'man-made features') are potential targets for InSAR deformation analysis. A-priori knowledge about the observation statistics of InSAR point scatterer measurements is necessary to give an independent quality description of the estimated (deformation) parameters. Using the Signal-to-Noise Ratio (SCR) from SAR images an a-priori estimate of the phase variance can be obtained. A controlled corner reflector experiment has been set up with leveling as an independent validation technique. In the period from March 2003 to June 2004 the movements of five corner reflectors in the area near Delft University of Technology have been monitored using leveling and repeat-pass InSAR (ERS-2 and Envisat). Double-difference observations, the first observations that bear interpretable information, are used for comparing the InSAR and leveling measurements. The stochastic model is set up as a variance-covariance matrix, estimating a-posteriori variance factors for the observation groups leveling, ERS-2 and Envisat. From the results it can be concluded that the a-priori phase variance based on SCR for the corner reflectors (σ ∼0.4mm) is significantly overestimated. The estimated a-posteriori InSAR phase standard deviation is 3.1 mm for Envisat and 3.9 mm for ERS-2 (mm, vertical). @en

Interferometric Synthetic Aperture Radar using Permanent Scatterers (PS-InSAR) [2] can be used for analyzing deformation patterns in time and space. 'Permanent Scattering' can be caused by different physical objects in the terrain. As PSs can be physically different, they may describe deformation patterns caused by different phenomena like gas extraction, ground water level variations or foundation instabilities. Separating superposed deformation signals is not trivial. The high precision of the phase data does not automatically lead to a reliable estimation of the deformation parameters. This paper gives a description of possible deformation causes and related scattering characteristics combined with a case study on separating deformation regimes. The results of a PS analysis performed on Rotterdam, the Netherlands, are used. Three classes of deformation mechanisms are discussed in relation with the corresponding scattering properties.@en