Sergi Duque

Polarimetric Differential SAR Interferometry: First Results With Ground-Based Measurements

The Remote Sensing Laboratory of the Universitat Politecnica de Catalunya carried out a one-year measuring campaign in the village of Sallent, northeastern Spain, using a polarimetric ground-based synthetic aperture radar (SAR) sensor. The objective was to study the subsidence phenomenon induced by the salt mining activity conducted in this area up to the middle of the last century. Zero-Baseline polarimetric SAR (PolSAR) data were gathered at X-band in nine different days, from June 2006 to March 2007. In this letter, the problem of extracting subsidence information from fully PolSAR acquisitions for the retrieval of high-quality deformation maps is addressed. After compensating for the atmospheric artifacts caused by troposphere changes, the linear component of the deformation process is estimated separately for each polarization channel with the Coherent Pixels Technique (CPT). Afterward, a novel polarimetric approach mixing the differential-phase information of each polarization channel is proposed. The results obtained in the two cases are quantitatively compared, and the advantages provided by the polarimetric acquisitions are finally stressed.

Single-Pass Bistatic SAR Interferometry Using Fixed-Receiver Configurations: Theory and Experimental Validation

In this paper, bistatic interferometry using fixed-receiver configurations is addressed both theoretically and experimentally. The analytical expressions for interferometric phase and height sensitivity are derived, and a full interferometric processing chain for digital elevation model (DEM) generation is presented. The derived expressions are general, and they can be applied to two possible acquisition geometries: backscattering and forward scattering. The theoretical developments are complemented with experimental results done with the bistatic receiver Synthetic Aperture radar Bistatic Receiver for INterferometric Applications. The obtained DEMs are compared with a DEM from the Shuttle Radar Topography Mission and a digital terrain model from the Institut Cartografic de Catalunya. The comparison allows one to validate the results and demonstrate to which particular features of the scene that the bistatic radar is sensitive.

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.

A bistatic SAR interferometric simulator for fixed receiver configurations

Bistatic SAR systems are an emerging research field. In which context, the Universitat Politecnica de Catalunya is developing a ground based bistatic system using ESAs ENVISAT and ERS-2 as transmitters. In this paper we characterize the bistatic interferometric phase and the different sources of decorrelation. We will also present a bistatic interferometric simulator which is able to generate realistic synthetic bistatic interferograms. The simulator is validated with real data obtained with our bistatic acquisition system, named SABRINA.

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,

Absolute Height Estimation Using a Single TerraSAR-X Staring Spotlight Acquisition

The work presented in this letter exploits the long synthetic aperture radar (SAR) of a single TerraSAR-X Staring Spotlight (ST) acquisition to derive absolute heights. Here, the slight azimuth defocusing effect due to height mismatch between the true height and the height assumed in SAR focusing is analyzed. The impact is almost negligible for most of acquisition modes. In contrast, spaceborne modes with very long aperture, such as the TerraSAR-X ST acquisition mode, present sensibility that can be used to retrieve absolute heights. The accuracy depends on incidence angle, orbit type, and mainly on signal-to-clutter ratio. Two different results are presented to demonstrate that absolute heights can be retrieved with accuracy of few meters using a single TerraSAR-X ST acquisition.

Bistatic SAR along track interferometry with multiple fixed receivers

This paper presents an along - track interferometry (ATI) study for a bistatic or multiestatic SAR configuration with fixed ground receivers. This technique can be useful for sea current estimation or for any problem of Ground Motion Target Indicator (GMTI). The proximity of the ground receivers to the scene allows to be very sensitivite to velocities with small baselines. This paper also proposes a multibaseline approach for ATI able to diferenciate among different velocity contributions in the same resolution cell. At the end of this paper, some results over real acquired bistatic data will be presented and discussed. The data have been acquired using the C-band SAR Bistatic Receiver for INterferometric Applications (SABRINA) and ESAs ENVISAT satellite, as a transmitter of opportunity.

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.

Bistatic SAR interferometry using ENVISAT and a ground based receiver: Experimental results

The Universitat Politecnica de Catalunya is developing a ground based bistatic system using ESAs ENVISAT and ERS-2 as transmitters. The spatial resolution of this configuration is similar to that of their monostatic counterpart, although foreshortening effects have a lesser impact. First single-pass interferometric images corresponding to a local test-site are presented and compared to a synthetic interferogram.

Single-Pass Tomography With Alternating Bistatic TanDEM-X Data

In this letter, the suitability of alternating bistatic (AB) TanDEM-X data for tomographic processing is demonstrated. The AB acquisition mode allows to acquire data from three different phase centers at the same time by means of a single pass of the TSX-1 and TDX-1 satellites. The channels of an AB acquisition present no temporal decorrelation within them. In addition, the atmospheric delay can be considered equal for all the channels. This letter analyzes the use of a single acquisition in the AB mode for tomographic processing. The theoretical analysis and the experimental result show that it is possible to separate different scattering mechanisms within a resolution cell under certain constraints.