[show abstract][hide abstract] ABSTRACT: Recently, the coherent scatterers (CSs) technique has been introduced in order to detect scatterers with a deterministic point-like scattering behavior in SAR images. Although the majority of the detected CSs show the typical properties of point-like scatterers, e.g., high amplitude, high interferometric coherence and low polarimetric entropy, some CSs present medium or even high polarimetric entropy. In this paper we study such cases by investigating the possibility that more than one Cs are present insides the resolution cell. We exploit not only the interferometric coherence but also the sublook coherence as a function of polarization states using the PolInSAR formalism and experimental data. For the case that the presence of more than one CS inside the resolution cell is found, the separation of CSs is implemented using a interferometric coherence model. In this work, airborne experimental datasets acquired at L-band by E-SAR system of the German Aerospace Center over the city of Munich in Germany are used.
Synthetic Aperture Radar (EUSAR), 2008 7th European Conference on; 07/2008
[show abstract][hide abstract] ABSTRACT: In the last decades several methods were developed for the estimation of Line of Sight (LOS) rotation angles of deterministic and distributed scatterers by exploiting radar polarimetry. Examples are the circular polarization algorithm proposed by Lee, the beta angle of the Cloude-Pottier polarimetric coherence matrix decomposition, the Cameron angle of the scatterer maximal symmetry axis, the minimum cross-polarization algorithm, the orientation of the maximum co-polarization state defined by Kenaugh/Huynen and its estimation through the Graves matrix or the polarization-ratio formalism by Boerner. Some of them are evaluated over extended while some over deterministic (or point-like) scatterers making use of first and/or second order polarimetric statistics, or using directly the information from the scattering matrix. In (1) the relationship between the different LOS estimates has been addressed on a numerical basis. All individual approaches may be divided into two main classes that are fundamentally different: the ones based on a Consimilarity Transformation (CTBR) and the ones based on a Rotation Transformation (RTBR). In this paper we further investigate the relationship between CTBR and RTBR and present now an analytic formulation. Although in many cases the estimation of LOS rotation angles through CTBR and RTBR is the same, this is not the case for general asymmetric scatterers. Motivated by the divergences of the approaches under different scatterers asymmetric conditions, new parameters are defined from the scattering matrix, which are related to the different kinds of asymmetry encountered (and possible to measure using polarimetry) on deterministic scatterers. The theoretical analysis is supported by the experimental validation using Coherent Scatterers (CSs) detected in SAR images. Coherent Scatterers are scatterers that have a point-like scattering behaviour and are detected through sublooks spectral correlation (2). Their deterministic behaviour justifies their application on the present study. For the experimental validation, data acquired by DLRs E-SAR system at L-band over the cities of Dresden and Munich are used. Emphasis is given in the detection and interpretation of symmetric and asymmetric (in terms of LOS rotations) Coherent Scatterers.
International Workshop on Applications of Polarimetry and Polarimetric Interferometry (Pol-InSAR); 01/2007
[show abstract][hide abstract] ABSTRACT: SAR images of urban areas are characterized by strong geometrical distortions (layover, foreshortening, shadowing) and a high diversity of mainly man-made scattering mechanisms. In order to simplify the analysis of SAR images in urban regions the Coherent Scatterers (CSs) technique has been proposed for the detection of scatterers with point-like behaviour. These deterministic scatterers allow the extraction of information in a simpler and more direct way. In this work, the detection and characterization of CSs at different frequencies and different polarizations is addressed. For that, airborne data acquired at L-, C- and X-band by the E-SAR system of the German Aerospace Center (DLR) over the city of Munich in Germany are used.
European Conference on Synthetic Aperture Radar (EUSAR); 05/2006
[show abstract][hide abstract] ABSTRACT: In this paper, a study concerning the comparison of several different procedures for the estimation of scatterers orientation angle for the coherent backscattering case is performed. Routines were proposed for the estimation of the orientation angle of distributed as well as of deterministic (coherent) scatterers. On deterministic scatterers it is expected that all routines converge to the same value, and we verify this statement. The procedures that can be applied to the general case of non-symmetrical scatterers were found out to belong to two main classes that are fundamentally different. We indicate the cases for which the classes of routines diverge due to their fundamental difference. The Coherent Scatterers (CSs) technique is used to support the analysis and confirm the existence of general non-symmetric point-like scatterers in SAR images of urban environments. For that, experimental data using the DLR's ESAR system at L-band over the city of Dresden, in Germany, is used.
European Conference on Synthetic Aperture Radar (EUSAR); 05/2006
[show abstract][hide abstract] ABSTRACT: The detection of scatterers with pointwise response in SAR images of urban areas using the so-called Coherent Scatterers (CSs) technique was in previous works introduced (1), (2). In this paper, the potential to exploit sub-aperture images from wide azimuth angular apertures (as it is the case for air- borne systems) to estimate CSs backscattering radiation patterns is addressed. The backscattering radiation pattern is modeled assuming a simple canonical class of scatterers. The model is then inverted using the estimated radiation patterns of individual CSs and their geometrical parameters are evaluated and related to CSs polarimetric properties. Two experiments using dihedral corner reflectors with differentt azimuth orientation and Line of Sight (LOS) rotation angles were performed, in order to verify the agreement with the theory. The data used are at L-band from the airborne E-SAR system of the German Aerospace Center (DLR) and the testsite is the Munich city in Germany. I. INTRODUCTION The Coherent Scatterers (CSs) technique to detect scatterers with point-like behaviour in SAR images of urban areas was introduced in (1), (2). Polarimetric and interferometric characterisation of CSs has been discussed, as well as the potential of physical and geometrical information extraction, as the estimation of the scatterers Line Of Sight (LOS) rotation angle and CSs dielectric properties. In (3) the backscattering radiation pattern in the azimuth direction of the so-called Permanent Scatterers (PSs) was estimated using ERS-2 image series and taking advantage of its loss of the on-board gyroscopes. This allowed to acquire images of the same scene with different azimuth aspect angles. A backscattering pattern model for canonical PSs was used to invert PSs geometrical parameters. In this work, azimuth backscattering radiation patterns of CSs are estimated using multi-look images from wide azimuth bandwidth systems. The backscattering radiation patterns are modeled as in (3) and the model parameters are inverted. Their relationship to the scatterer's type estimated through polarimetry is investigated. Finally, two experiments using dihedral corner reflectors were performed, in order to verify the agreement with the theory.
IEEE Geoscience and Remote Sensing Symposium (IGARSS); 01/2006