Freek J. van Leijen

Phase Estimation for Distributed Scatterers in InSAR Stacks Using Integer Least Squares Estimation

In recent years, new algorithms have been proposed to retrieve maximum available information in synthetic aperture radar (SAR) interferometric stacks with focus on distributed scatterers. The key step in these algorithms is to optimally estimate single-master (SM) wrapped phases for each pixel from all possible interferometric combinations, preserving useful information and filtering noise. In this paper, we propose a new method for SM-phase estimation based on the integer least squares principle. We model the SM-phase estimation problem in a linear form by introducing additional integer ambiguities and use a bootstrap estimator for joint estimation of SM-phases and the integer unknowns. In addition, a full error propagation scheme is introduced in order to evaluate the precision of the final SM-phase estimates. The main advantages of the proposed method are the flexibility to be applied on any (connected) subset of interferograms and the quality description via the provision of a full covariance matrix of the estimates. Results from both synthetic experiments and a case study over the Torfajökull volcano in Iceland demonstrate that the proposed method can efficiently filter noise from wrapped multibaseline interferometric stacks, resulting in doubling the number of detected coherent pixels with respect to conventional persistent scatterer interferometry.

Semi-Automated Monitoring of a Mega-Scale Beach Nourishment Using High-Resolution TerraSAR-X Satellite Data

This paper presents a semi-automated approach to detecting coastal shoreline change with high spatial- and temporal-resolution using X-band synthetic aperture radar (SAR) data. The method was applied at the Sand Motor, a “mega-scale” beach nourishment project in the Netherlands. Natural processes, like waves, wind, and tides, gradually distribute the highly concentrated sand to adjacent beaches. Currently, various in-situ techniques are used to monitor the Sand Motor on a monthly basis. Meanwhile, the TerraSAR-X satellite collects two high-resolution (3 × 3 m), cloud-penetrating SAR images every 11 days. This study investigates whether shorelines detected in TerraSAR-X imagery are accurate enough to monitor the shoreline dynamics of a project like the Sand Motor. The study proposes and implements a semi-automated workflow to extract shorelines from all 182 available TerraSAR-X images acquired between 2011 and 2014. The shorelines are validated using bi-monthly RTK-GPS topographic surveys and nearby wave and tide measurements. A valid shoreline could be extracted from 54% of the images. The horizontal accuracy of these shorelines is approximately 50 m, which is sufficient to assess the larger scale shoreline dynamics of the Sand Motor. The accuracy is affected strongly by sea state and partly by acquisition geometry. We conclude that using frequent, high-resolution TerraSAR-X imagery is a valid option for assessing coastal dynamics on the order of tens of meters at approximately monthly intervals.

The impact of ground-based uncorrelated radio frequency interference (RFI) sources on satellite radar interferometric ground motion analysis

The telecommunications sector has proposed to use the 5.350-5.470 GHz frequency band for ground-based communication services. The Sentinel-1, RadarSAT-2, and future RadarSAT constellation SAR satellites are operating in the same band. Here we assess the impact of these ground-based uncorrelated radio frequency interference (RFI) sources to radar interferometry-based ground motion analysis. Apart from a theoretical assessment, a Persistent Scatterer Interferometry analysis is performed based on a combination of real ENVISAT data and simulated RFI noise at different levels. The analysis shows that the RFI sources significantly reduce the applicability of radar interferometry, with a reduction of detected Persistent Scatterers with more than 50%. If the telecommunication sector would proceed with this plan, operational ground motion services based on Sentinel-1 data would no longer be possible.

InSAR datum connection using GNSS-augmented radar transponders

Deformation estimates from Interferometric Synthetic Aperture Radar (InSAR) are relative: they form a ‘free’ network referred to an arbitrary datum, e.g. by assuming a reference point in the image to be stable. However, some applications require ‘absolute’ InSAR estimates, i.e. expressed in a well-defined terrestrial reference frame, e.g. to compare InSAR results with those of other techniques. We propose a methodology based on collocated InSAR and Global Navigation Satellite System (GNSS) measurements, achieved by rigidly attaching phase-stable millimetre-precision compact active radar transponders to GNSS antennas. We demonstrate this concept through a simulated example and practical case studies in the Netherlands.

Towards product-level performance models for Sentinel-1 follow-on missions: Deformation measurements case study

The potential of differential SAR interferometry (D-InSAR) techniques for the study of the 3-D deformation phenomena has been extensively demonstrated. In particular, two different performance approaches (one analytical and one numerical solutions) have been implemented and analyzed. The primary objective is to investigate the capabilities of the Sentinel-1 follow-on SAR mission (named here HRWS) and its preferred acquisition modes for this particular application domain, which might help to the mission optimization.

L-band multistatic radar interferometry for 3D deformation vector decomposition

SAOCOM is an Argentinian L band system formed by two satellites (SAOCOM-1A and SAOCOM-1B). ESA is investigating the possible applications of a companion satellite (SAOCOM-CS) carrying a passive receiver working in concert with one of the SAOCOM-1 satellites. During the mission there will be cycles with a long along-track bistatic baseline, suitable for deformation monitoring. Together with the combination of ascending and descending orbits, this geometry will produce four measurements from different viewing geometries, enabling us to estimate the 3D motion vector. Here we investigate the sensitivity of such a configuration, and the opportunities for increasing the density of persistent scatterers.

One-dimensional radar interferometry for line infrastructure

Here we present an efficient algorithm to analyze the deformation behavior of line infrastructure, such as water defense structures and railways, using radar interferometric time series. Due to the limited amount of pixels and the consistent reflection properties, a detailed analysis can be performed. By considering neighboring pixels, the influence of a large part of error sources is reduced. However, the strong correlation between pixels should be considered. The algorithm is applied to dikes in the Netherlands, showing global as well as local deformation effects.

A standardized approach for the integration of geodetic data for deformation analysis

This contribution proposes a new approach for the analysis and preparation of geodetic data for the use in geophysical modeling. The approach resolves the problem of non-uniformity in the datasets obtained by different measurement techniques. The approach is based on two main steps: uniformization of the data using a standardized data format, and the application of the CUPiDO conversion tool to construct double-difference observations. Both steps are described in detail. By using double-difference observations, the effect of different reference points and geodetic datums is eliminated, thereby making the outcomes of the CUPiDO tool well suited for an integrated inversion to estimate a model. The CUPiDO tool will be made publicly available.

Land deformation monitoring using PS-InSAR technique over Sahel-Doukkala (Morocco)

Even if land deformation in Sahel-Doukkala may not directly threaten human life, it could lead to serious economic losses. Therefore, the monitoring of this deformation becomes a priority. In this study, PS-InSAR technique was applied in order to extract information regarding land deformation. This method was successful in detecting a considerable amount of PS targets from which the land deformation was estimated. The deformation rate was between −2.4 mm/year and 1.9 mm/year showing an alternation between uplift and subsidence. The origin of this deformation is suggested to be related to tectonic and climatological origins.