Walid Tabbara

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On Different Interferometric Coherence Optimization Methods

The interferometric coherence optimization methods are based on the definition of projection vect... more The interferometric coherence optimization methods are based on the definition of projection vectors, which is the way to combine the information occuring from the polarimetric channels of both interferometric images. An important point is the physical interpretation of the projection vectors in terms of scattering characteristics. An optimization algorithm has been first proposed by Cloude and Papathanassiou(referred as C & P algorithm [2]) , based on the selection of the best pair of projection vectors. The C & P algorithm leads to a 3 × 3 complex eigenvector problem, each projection vector representing a selected mechanism for each image. We prove first that the C & P algorithm corresponds mathematically to the most general optimization of the interferometric coherence. This means that the interferograms formed by using these mechanisms have the highest possible coherence. Nevertheless a major drawback of the C & P algorithm is that in neighboring resolution cells the optimal sca...

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A Full Wave Three Dimensional Analysis of Forest Remote Sensing Using VHF Electromagnetic Wave

Progress In Electromagnetics Research, 2002

A forest made of an infinite biperiodic array of trees over a lossy ground, is illuminated by a l... more A forest made of an infinite biperiodic array of trees over a lossy ground, is illuminated by a linearly polarized electromagnetic plane wave in the range of 20 to 90 MHz. Due to the ratio of the wavelength to the array period, only the specular mode is propagative. Therefore, a reflection coefficient is computed and not a backscattering coefficient. It is obtained by means of a full wave approach, based on an integral representation of the electric field. This approach takes into account all possible interactions between each component of the medium as well as ground penetration and provides full information on the phase of the scattered field. Two models of the forest are developed, the two layers one where trees are separated and the four layers one whee the canopy is replaced by an equivalent homogeneous medium. The low frequency (VHF) used here make this homogenization possible and allows one to consider trees with simple shape, the wave being unable to sense details of a tree. 3.4 Resolution of the Integral Equation by a Method of Moment 3.5 Calculation of the Reflection Coefficient R 4 Numerical Results 4.1 Validity of the Born Approximation 4.2 Influence of the Age of the Trees 4.3 Influence of the Representation of the Trees 5 Conclusion Appendix A. The Dyadic Green's Function for the 2LM and the 4LM A.1 The Dyadic Green's Function for the 2LM A.2 The Dyadic Green's Function for the 4LM Appendix B. Elements of the Matrix [I kj ] References

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Reconstruction d’obstacles métalliques de forme simple

Annales des Télécommunications

Walid TABBARA Docteur-ds-Sciences ** de forme simple* Dans cet article est d$crite une m~thode pe... more Walid TABBARA Docteur-ds-Sciences ** de forme simple* Dans cet article est d$crite une m~thode permettant par analyse multifr$quentielle du champ r~trodiffus~ par un obstacle parfaitement conducteur, de reconstruire totalement ou partiellement la forme de la cible. La m~thode est basde sur l'approximation de l'optique physique. Aprbs le rappel des dquations de base, l'~tude du cas de la sphbre permet de d6terminer les parambtres d'int~r6t pratique (bande spectrale, nombre de fr~quences, donn~es bruitdes). On $tudie la stabilitd de la reconstruction lorsque ces parambtres varient.

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$Research paper thumbnail of Diffraction par des ouvertures dans la paroi d’un obstacle conducteur. Les différentes approches usuelles du problème$

Diffraction par des ouvertures dans la paroi d’un obstacle conducteur. Les différentes approches usuelles du problème

Annales des Télécommunications, 1979

Analyse L’étude de la diffraction d’une onde électromagnétique par un obstacle conducteur compor... more Analyse L’étude de la diffraction d’une onde électromagnétique par un obstacle conducteur comportant des ouvertures dans sa paroi est d’un grand intérêt pratique et connaît actuellement un regain d’intérêt. Les méthodes considérées dans cette étude sont très variées et ne présentent pas toutes des avantages identiques. Aussi estil intéressant de les passer en revue, pour en délimiter les domaines d’application ainsi que leurs possibilités d’application. L’auteur présente les méthodes rigoureuses et approchées et il les illustre par des exemples. Abstract The problem of electromagnetic wave interaction with conducting bodies having apertures in their surfaces is of a great practical interest and is now the purpose of great attention. The various methods described here do not present the same advantages. Thus it is interesting to review them in order to define their range of applications. The author presents rigorous and approximate methods and he illustrates them by different examples.

A MoMTD/FDTD hybrid method to calculate the SAR induced by a base station antenna

IEEE Antennas and Propagation Society International Symposium. Transmitting Waves of Progress to the Next Millennium. 2000 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.00CH37118), 2000

A method of moments in the time domain/finite difference time domain (MoMTD/FDTD) hybrid method h... more A method of moments in the time domain/finite difference time domain (MoMTD/FDTD) hybrid method has been used to calculate the radiation of a helix antenna and validated. A solution has been suggested for the problem of materials crossing at the interface between the two methods. The results are stable, but the accuracy still needs to be improved. The calculation of

$Research paper thumbnail of Refractive index profile and target reconstruction a time and spectral domain integral equation approach$

Refractive index profile and target reconstruction a time and spectral domain integral equation approach

1979 Antennas and Propagation Society International Symposium

A new parameter for IFPOL coherence optimization methods

IGARSS 2003. 2003 IEEE International Geoscience and Remote Sensing Symposium. Proceedings (IEEE Cat. No.03CH37477)

ABSTRACT

$Research paper thumbnail of Diffraction tomography some applications and extension to 3-D ultrasound imaging$

Diffraction tomography some applications and extension to 3-D ultrasound imaging

Lecture Notes in Mathematics, 1991

Diffraction tomography is investigated in our laboratory since the beginning of the eighties. We ... more Diffraction tomography is investigated in our laboratory since the beginning of the eighties. We first present an overview of the results obtained at microwave and ultrasound frequencies. Next, since the authors are mainly involved in acoustical imaging, we emphasize the extension of this technique to 3D imaging using ultrasound waves.

Comparison between simulations and interferometric polarimatric SAR P-band data on a pine-trees forest

IEEE International IEEE International IEEE International Geoscience and Remote Sensing Symposium, 2004. IGARSS '04. Proceedings. 2004

ABSTRACT The interpretation of SAR data remains particularly difficult in case of forests, which ... more ABSTRACT The interpretation of SAR data remains particularly difficult in case of forests, which makes the use of modelling very helpful. On the other hand, the potential of combined use of interferometric and polarimetric data has been already demonstrated to provide key forest parameters. In this paper, we present comparisons between interferometric polarimetric images of a forest simulated by a coherent scattering model derived from L. Thirion (2003) and L. Thirion (2004), and real airborne and full polarimetric interferometric P-band data measured over maritime pine trees. Results are presented that demonstrate the efficiency of the model to retrieve polarimetric and interferometric parameters on this forest. Finally, a first step of simplification and inversion of the model, relying on the analysis of the scatterers contributions, is proposed

Crosstalk prediction on wire bundles by Kriging approach

IEEE International Symposium on Electromagnetic Compatibility. Symposium Record (Cat. No.00CH37016)

A wide variety of interconnections among electronic devices are performed by means of randomly tw... more A wide variety of interconnections among electronic devices are performed by means of randomly twisted bundle of wires, particularly for transport and industrial applications. This work examines the crosstalk analysis of such bundles. A new model based on fractals for describing the position of wires winding throughout a bundle is presented. It allows the wires' meandering degree to be tuned simply by means of a parameter (the fractal dimension). It also allows for a statistical analysis of crosstalk because it can simulate independent different realizations of the same interconnection. An efficient multifactor prediction method known as "Kriging" is applied in order to describe the crosstalk as a function of the input factors (cable loads, cable height above the ground plane, etc.) of the cable model. It allows for a drastic reduction in the simulation time insofar as it predicts the crosstalk at untried combinations of the input factors from a small base of input combinations. In comparing the crosstalk simulated using the fractal model with the experimental measurements good agreement was found.

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Electromagnetic energy coupled to a monopole inside a perfectly conducting rectangular cavity

23rd European Microwave Conference, 1993, 1993

ABSTRACT The electromagnetic energy coupled to a monopole placed inside a cavity with an aperture... more ABSTRACT The electromagnetic energy coupled to a monopole placed inside a cavity with an aperture on one side is determined numerically and experimentally. Combining the equivalent dipole method for the aperture and an integral equation solution for the currents on the monopole, the voltage at the base of the latter is obtained over a large frequency band. The voltage sensitivity to the reaction of the field scattered, by the monopole and the inside walls, of the cavity on the field distribution in the aperture on one hand, and on the other hand to the accuracy of the design parameters of the cavity, is analyzed. Comparison with experimental results is done throughout this presentation.

Analyse de quelques approximations utiles à la caractérisation acoustique du fond marin

Editions de Physique, ISSN : 0988-4319International audienceDiscussion de la validité de trois ap... more Editions de Physique, ISSN : 0988-4319International audienceDiscussion de la validité de trois approximations du champ acoustique diffracté par une structure stratifiée plane (fluide/fluide/solide) modélisant un fond marin (eau/sédiment/socle): basse fréquence, haute fréquence, WKB. Simulations numériques à partir de configurations différentes du fond (SCTBG

$Research paper thumbnail of Problèmes unidimensionnels de diffraction inverse en acoustique et en électromagnétisme. Etude bibliographique$

Problèmes unidimensionnels de diffraction inverse en acoustique et en électromagnétisme. Etude bibliographique

Les Editions de Physique, ISSN : 0988-4319International audienceAnalyse bibliographique de la sol... more Les Editions de Physique, ISSN : 0988-4319International audienceAnalyse bibliographique de la solution du problème inverse de diffraction dans le cas d'une lame ou d'un demi-espace inhomogène: méthodes Gelfand-Levitau-Marchenko, déductives, itératives, approchées, sismiques,... Discussion des références, des conditions d'application des méthodes et de leurs limites. (CSTBG

Exact and approximate probing of sea-bottom

Proceedings., IEEE Ultrasonics Symposium

Investigated are two methods for the reconstruction of the acoustic profiles of a plane-stratifie... more Investigated are two methods for the reconstruction of the acoustic profiles of a plane-stratified structure that model the ocean floor (sediment/subbottom) from reflected fields. The first method is based on a geometrical acoustics approximation. The acoustical parameters of an absorbing layered medium (fluid-solid) are retrieved from the plane-wave reflection coefficients obtained at several incidences and frequencies. Numerical simulations are carried

A theoretical model of propagation in forest compared with experimental results

Proceedings. 2005 IEEE International Geoscience and Remote Sensing Symposium, 2005. IGARSS '05.

Propagation of electromagnetic waves in forest medium is examined in a frequency band of 100 to 3... more Propagation of electromagnetic waves in forest medium is examined in a frequency band of 100 to 300MHz. We propose a simplified model to represent the medium in this frequency band. We have developed an exact method to calculate the electromagnetic field received inside or outside the forest medium when the transmitter is placed among or in front of the trees. Comparisons between simulation and measurement made in anechoic chamber are done to test and validate the theoretical method. Models for the analysis of the propagation of electromag- netic waves through forest have been studied for a long time to understand the effects of the different elements of this complex medium. These effects depend largely on the frequency of the incident wave. At low frequencies (<90MHz), the dimensions of the elements of the canopy (small branches and leaves) are small compared to the wavelength, these elements are transpar- ent to the incident wave and their effects are negligible on the propagating wave. The forest medium is modeled by dielectric homogeneous layers representing the ground, the vegetation layer (trunks, branches ...) , the air and the ionosphere (1), (2). When we consider high frequencies (>500MHz), the elements of the medium are modeled by cylinders (trunks, branches) and ellipsoids (leaves) and the scattering from each element is computed using methods like radiative transfer theory (3). In this paper, we study the propagation of waves in the range of 100 - 300MHz, where both the transmitting and receiving antennas are in the vegetation layer. We have developed a full wave method that takes into account all the interactions between the different elements of the medium. Our model is based on the domain integral representation of the electric field. To validate our theoretical model, we have compared our simulated results with measurements conducted at ON- ERA in an anechoic chamber using a scaled model of the representation of the medium. To account for the differences between the dimensions of the real and the scaled media, the band of frequency is chosen so that the ratio between the wavelengths in the real case and in the measurements is equal to the ratio between the dimensions of the model and the dimensions of the scaled model respectively. In section 2 we present the theoretical method we have developed to model the propagation in the forest medium and we propose a simplification to reduce the computing time. In section 3, we present the results of simulations and we compare their results with those provide by the measurements. Conclusion and prospects are given in section 4. II. THE THEORETICAL MODEL

Reflection From Quasi-Randomly Distributed Gratings of Fibers: Comparison of Integral-Representation With Homogenization Methods

Journal of Electromagnetic Waves and Applications, 1997

ABSTRACT The reflectivity of quasi-randomly distributed gratings of fibers is analyzed by means o... more ABSTRACT The reflectivity of quasi-randomly distributed gratings of fibers is analyzed by means of an integral representation of the scattered field. The results are compared with those obtained from two homogenization methods and used to investigate the accuracy of the latter. Both TE and TM polarizations are considered and the reflectivity is investigated as a function of the wavelength and the angle of incidence.

Coherence Optimization Methods for Scattering Centers Separation in Polarimetric Interferometry

Journal of Electromagnetic Waves and Applications, 2005

... The principal difficulty then is that a target is not necessarily made of some very bright po... more

Kriging the quantile: application to a simple transmission line model

Inverse Problems, 2002

ABSTRACT The deterministic analysis of coupling between wireless communication systems and sensit... more ABSTRACT The deterministic analysis of coupling between wireless communication systems and sensitive electronic devices connected by means of cables is intricate because of the variability of geometry. A statistical approach appears to be more appropriate. Application of such an approach is illustrated by the study of a simple transmission line illuminated by a plane wave at random incidence and polarization. The latter is used to estimate the upper bound of the current magnitude at a given probability level in terms of the geometric configuration. Moreover, realistic problems will require intense computational effort. Design of experiments and interpolation may be efficient tools to save CPU time and memory. Kriging, which couples both techniques, has been applied to the above simple transmission line. Different covariance functions have been used and compared in order to see which model appears to be more suitable for such an application. Reliable prediction has been obtained for the quantile.

Boosting Predictions by Calibration of Traffic Model and Learning of Indicators' Distributions

IEEE Transactions on Vehicular Technology, 2008

In this paper, we discuss a two-step scheme using measurements that are taken on a real network. ... more In this paper, we discuss a two-step scheme using measurements that are taken on a real network. The two steps are complementary and aim to enhance the precision and the quality of a radio network planning tool. We have, in a first step, calibrated the tool by means of live traffic data and/or measurements that are taken on the air interface of a real network and are processed to calculate the traffic values on each cell. We show that the availability of real data is highly valuable since it provides a more detailed view of the network behavior and performance. In a second step, we have proposed a novel algorithm based on a fuzzy Bayesian framework to ameliorate the generalization of a distribution learning system. The learning system aims to correct the predictions of the planning tool and uses the information contained in the simulations as well as the knowledge of the measurements to learn a relation function. The fuzzy Bayesian clustering algorithm is a preprocessing technique that divides the whole learning space into subspaces, where the capacity of the learning system to predict unobserved configurations (generalization) is better performed.

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Probing of a Stratified Medium by Means of a Magnetic Dipole: A Geometrical Optics Approach

IEEE Transactions on Geoscience and Remote Sensing, 1985

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Walid Tabbara

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