Daniel Carrasco

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.

InSAR volcano and seismic monitoring in Spain. Results for the period 1992–2000 and possible interpretations

Abstract In September 1999, we started a demonstration of the operational use of InSAR technology in the routine volcano monitoring procedures in Spain for the European Space Agency. This project was complemented with national funding to face the seismic activity. The effort focuses on the Canary Islands and the southern part of the Iberian Peninsula (volcanic and seismic cases, respectively) to supplement the traditional geodetic techniques used to date. We present the results obtained and the first interpretation of the obtained displacements. The research in volcanism is mainly focused on Tenerife Island, where a historical analysis with more than 20 images, from 1992 to 2000 has been done. The observed deformations (unknown to date) in the different interferograms are associated to the zones of the most recent activity in the island. In connection with seismic hazards we have studied displacements associated with the December 23, 1993 earthquake (magnitude Mb =5.0) produced between Adra and Berja cities. This earthquake was extensively felt in Spain, producing some damages on the epicentral zone with maximum intensity of VII (MSK). Our results clearly show the need for InSAR techniques to be included systematically as an operational component whenever possible. It would be a powerful and cost-effective way of supplementing the techniques normally used in geodetic monitoring.

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,

Usage of multitemporal filtering of SAR images for change detection

A methodology for change detection of artificial features using multitemporal series of SAR data is presented. The methodology uses time averaging of data from ERS-2 and Envisat yielding improved radiometric quality which highly improves the photointerpretability. The methodology is tested in several scenarios in the context of security applications when data needs to be gathered during cloudy season when optical satellites are unable operate. The results have been validated with very high resolution optical data from summer season.