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Radar interferometry techniques for the study of ground subsidence phenomena: a review of practical issues through cases in Spain

Subsidence related to multiple natural and human-induced processes affects an increasing number of areas worldwide. Although this phenomenon may involve surface deformation with 3D displacement components, negative vertical movement, either progressive or episodic, tends to dominate. Over the last decades, differential SAR interferometry (DInSAR) has become a very useful remote sensing tool for accurately measuring the spatial and temporal evolution of surface displacements over broad areas. This work discusses the main advantages and limitations of addressing active subsidence phenomena by means of DInSAR techniques from an end-user point of view. Special attention is paid to the spatial and temporal resolution, the precision of the measurements, and the usefulness of the data. The presented analysis is focused on DInSAR results exploitation of various ground subsidence phenomena (groundwater withdrawal, soil compaction, mining subsidence, evaporite dissolution subsidence, and volcanic deformation) with different displacement patterns in a selection of subsidence areas in Spain. Finally, a cost comparative study is performed for the different techniques applied.

Advances on DInSAR with ERS and ENVISAT Data using the Coherent Pixels Technique (CPT)

In this paper, improvements on the Coherent Pixels Technique (CPT) for deformation phenomena monitoring are presented. Advances are made in the different steps of the algorithm (from data selection to their processing) improving quality of the results and computational time. Deformation results of different studied areas are presented revealing the power of DInSAR techniques for risk management and for the understanding of much geological process.

Application of the coherent pixels technique to the generation of deformation maps with ERS and ENVISAT data

In this paper, a modification of the Coherent Pixels Technique (CPT) to work with both ERS and ENVISAT images will be presented. CPT is able to retrieve the linear and nonlinear components of movement from a set of low resolution interferograms (multi-looked), estimating at the same time the DEM error and the atmospheric artifacts. The pixel selection criterion originally implemented is based on its coherence stability in the stack of interferograms, in consequence the final product will have lower resolution than the original images and interferograms with short baselines and compatible Dopplers will be preferred to maximize the number of selected pixels. As the algorithm is not affected by the presence of subsets of disconnected interferograms the inclusion of ENVISAT data to the existing ERS datasets is quite straightforward. The modifications included in the algorithm to work with different sensors are presented and validation results over the city of Paris (France) discussed. Keywordsdifferential interferometry, subsidence monitoring, ERS, ENVISAT,

Orbital SAR simulator of fishing vessel polarimetric signatures based on high frequency electromagnetic calculations

This paper continues the work developed in related to a numerical tool able to simulate the full-polarimetric raw data for a given orbital SAR system from a realistic vessel model. This simulator makes possible the construction of a precise database of vessel radar signatures that will be used to develop classification algorithms. The simulator will be also useful to determine the system parameters of a future orbital SAR sensor dedicated to sea activity monitoring. This paper is focused on the validation tests and the new improvements developed.

DInSAR monitoring of land subsidence in Orihuela City, Spain: Comparison with geotechnical data

An advanced DInSAR technique called Coherent Pixels Technique (CPT) has been used to measure the subsidence existing in Orihuela city (Spain) during the period 1993-2001 due to ground water level fall. The estimated subsidence, with values lower than 7 cm, is highly influenced by soil geotechnical conditions like the deformable soil thickness. In addition, the wells location is an important subsidence factor because they are directly related to a decrease of the piezometric level.

Estimation of the Deformation Temporal Evolution Using Airborne Differential SAR Interferometry

This paper presents airborne DInSAR results using a stack of 14 images, which were acquired by the Experimental SAR (E-SAR) system of the German Aerospace Center (DLR) during a time span of only three hours and fifteen minutes. An advanced differential technique is used to retrieve the error in the digital elevation model (DEM) and the temporal evolution of the deformation for every coherent pixel in the image. Furthermore, some modifications in the differential processing chain are included to deal with the existence of the so-called residual motion errors, which play a similar role as atmospheric artifacts in the spaceborne case. The detected deformation of a corner reflector and of some agricultural fields allows to validate the proposed techniques to measure deformation phenomena with an airborne platform.

Simulation of fishing vessels polarimetric signatures as first step to vessel classification

This paper presents a numerical tool able to generate realistic SAR images from accurate vessel models for a given orbital sensor. Its capability to extract high resolution radar signatures converts this SAR simulator in a useful tool for vessel classification studies and, furthermore, to define a future constellation of SAR sensors bound for carry on an automatic vessel monitoring system. This SAR simulator has low computational requirements as it is based on high frequency electromagnetic calculations making feasible to run it in a simple PC. In this paper, the main scheme of the simulator and its capability to consider the vessel velocity and the ocean waves, which can produce an important distorting effect in the final SAR images, will be presented as well as some validation results and particular aspects of vessel modeling. Finally, some examples of radar signatures of precise fishing vessel models are exposed.

Application of the Coherent Pixels Technique (CPT) to urban monitoring

During the past years, Remote Sensing has become a powerful tool for earth observation. In particular, SAR differential interferometry (DInSAR) has shown to be a very reliable technique for deformation phenomena monitoring, being able to achieve millimetric accuracies. It is the aim of this paper to present and show the potentials of the UPCs advanced DInSAR algorithm, the coherent pixels technique (CPT). Deformation results of different studied areas will be presented, revealing the performances of DInSAR for risk management as well as for the understanding of much geological processes.

Phase statistics and quality evaluation of deformation maps with multiple-image differential interferometry

This paper presents a closed formulation to evaluate the quality of terrain deformation maps obtained with multi-image differential interferometry. The analytical formulation, based on the application of the asymptotic covariance matrix, that propagates the interferogram coherences to the linear deformation and DEM error accuracies when using a stack of interferograms, is developed and validated with real data from the ERS satellites.

Electromagnetic scattering measurements on a fractal surface

In this paper we present a procedure devoted to validate innovative theories on the electromagnetic scattering from natural surfaces, using fractal functions for the surface description. A fractal surface has been built as a superposition of cardboard and aluminium layers, according with a computer design based on the Weierstrass-Mandelbrot (WM) fractal function. Its statistical properties have been verified with optical measurements. The electromagnetic field scattered at X band from the built surface has been measured in controlled environment as a function of the incidence angle. Obtained results have been compared with those of the Kirchhoff Approximation (KA) and the Small Perturbation Method (SPM) in conjunction with the fractional Brownian motion (fBm). Congruence and discrepancies of measured data with theoretical results are discussed, providing a validation of the methods