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The Gaussian Beam Summation and the Gaussian Launching Methods in Scattering Problem

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Journal of Electromagnetic Analysis and Applications 2016年第10期8卷 219-225页

作者： Papa Ousmane Leye ali khenchaf Philippe Pouliguen Lab-STICC UMR CNRS 6285 ENSTA Bretagne Brest France French General Directorate for Armament (DGA) Bagneux France

This paper is mainly devoted to application of the Gaussian beam summation technique in electromagnetic simulations problem. Gaussian beams are asymptotic solutions of the Helmholtz equation within the paraxial approximation. Since they are insensitive to ray transition region, several techniques based on Gaussian beam are used to evaluate high frequency EM wave equation, which overcome partially or fully the difficulties of singular regions (caustics, zero field in shadow zones). This paper concentrates on the explicit formulation of the electromagnetic field scattered from radar target. In this approach, when the incident field illuminates the target, the scattering is accounted in a complex weighing function. The wave field at a receiver is evaluated as superposition of Gaussian beams concentrated close to rays emerging from the target, passing through the neighbor of the receiver.

关键词： Gaussian Beams RCS Scattering Radar Targets

Modelling of High-Frequency Roughness Scattering from Various Rough Surfaces through the Small Slope Approximation of First Order

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Open Journal of Acoustics 2012年第1期2卷 1-11页

作者： Virginie Jaud Cedric Gervaise Yann Stephan ali khenchaf GIPSA-LAB SIGMAPHY French National Centre for Scientific Research Grenoble France Passive Acoustics Superior National School of Advanced Techniques of Brittany Brest France The Naval Hydrographic and Oceanographic Service Brest France

The first-order small slope approximation is applied to model the scattering strength from a rough surface in underwater acoustics to account for seafloor for high frequencies from 10 kHz to hundreds of kilohertz. Emphasis is placed on simulating the response from two-dimensional anisotropic rough surfaces. Several rough surfaces are described based on structure functions such as the particular sandy ripples shape. The scattering strength is predicted by the small slope approximation and is first compared to a well known bistatic method, interpolating the Kirchhoff approximation and the small perturbations model, assuming that the rough interface is isotropic. Results obtained from the two different models are similar and show a higher level in the specular direction than in the other directions. For an isotropic surface, changing the propagation plane gives similar results. Then, SSA, which lets us adapt the structure function of the roughness straight away, is tested trough several anisotropic surfaces. In a longitudinal direction of ripples, the scattering strength is mostly in the specular direction, whereas in the transversal direction of ripples, the scattering strength prediction shows high values for different angular directions. Thus the scattering strength is spread in a very different way strictly related to the particular features of the ripples. Combine our results, indicates the importance of taking into account the anisotropy of a surface in a scattering prediction process, taking into account the positions of the emitter and of the receiver which are naturally significant when predicting scattering strength.

关键词： Anisotropy Roughness Scattering Small Slope Approximation

Exploitation of Electromagnetic Models for Sea Wind Speed Estimation from C-Band Sentinel-1 Images

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Journal of Electromagnetic Analysis and Applications 2016年第3期8卷 42-55页

作者： Tran Vu La ali khenchaf Fabrice Comblet Carole Nahum Helmi Ghanmi Lab-STICC UMR CNRS 6285 ENSTA Bretagne Brest France French General Directorate for Armament (DGA) Paris France

Among the different available wind sources, i.e. in situ measurements, numeric weather models, the retrieval of wind speed from Synthetic Aperture Radar (SAR) data is one of the most widely used methods, since it can give high wind resolution cells. For this purpose, one can find two principal approaches: via electromagnetic (EM) models and empirical (EP) models. In both approaches, the Geophysical Model Functions (GMFs) are used to describe the relation of radar scattering, wind speed, and the geometry of observations. By knowing radar scattering and geometric parameters, it is possible to invert the GMFs to retrieve wind speed. It is very interesting to compare wind speed estimated by the EM models, general descriptions of radar scattering from sea surface, to the one estimated by the EP models, specific descriptions for the inverse problem. Based on the comparisons, some ideas are proposed to improve the performance of the EM models for wind speed retrieval.

关键词： C-Band Synthetic Aperture Radar (SAR) Electromagnetic (EM) Scattering Models Radar Cross-Section (RCS) Remote Sensing Small Perturbation Model (SPM) Sea Surface Wind

GLRT Detection for Range and Doppler Distributed Targets in non-Gaussian Clutter

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GLRT Detection for Range and Doppler Distributed Targets in ...

Influence of Synchronization Impairments on an Experimental TDOA/FDOA Localization System

2006 CIE International Conference on Radar

作者： Nicolas Bon ali khenchaf René Garello Jean-Michel Quellec Laboratoire E3I2-EA 3876 2 rue Francois Verny 29806 Brest cedex 9France GET-ENST Bretagne Technopo le Brest Iroise-CS 83818 29238 Brest cedexFrance Thales Airborne Systems BP 58324 29283 Brest cedexFrance

A Generalized likelihood ratio test （GLRT） is derived for adaptive detection of range and Doppler distributed *** clutter is modelled as a Spherically Invariant Random Process （SIRP） and its texture component is range dependent （heterogeneous clutter）.We suppose here that the speckle component covariance matrix is known or estimated thanks to a secondary data ***,unknown parameters to be estimated are local texture values,the complex amplitudes and frequencies of all scattering *** proposed detector assumes a priori knowledge on the spatial distribution of the target and has the precious property of Constant False Alarm Rate （CFAR） with the assumption of a known speckle covariance matrix or by the use of frequency agility.

关键词： Clutter Radar scattering Detectors Speckle Covariance matrix Frequency estimation Radar detection Fluctuations Random processes Spatial resolution

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Journal of Electrical Engineering 2017年第1期5卷 1-9页

作者： Hugo Seute Cyrille Enderli Jean-Francois Grandin ali khenchaf Jean-Christophe Cexus Thales Airborne Systems 2 Avenue Gay Lussac 78990 Elancourt FRANCE Lab-STICC UMR CNRS 6285 ENSTA Bretagne 2 Rue Francois Verny 29806 Brest FRANCE

In Electronic Warfare, and more specifically in the domain of passive localization, accurate time synchronization between platforms is decisive, especially on systems relying on TDOA （time difference of arrival） and FDOA （frequency difference of arrival）. This paper investigates this issue by presenting an analysis in terms of final localization performance of an experimental passive localization system based on off-the-shelf components. This system is detailed, as well as the methodology used to carry out the acquisition of real data. This experiment has been realized with two different kinds of clock. The results are analyzed by calculating the Allan deviation and time deviation. The choice of these metrics is explained and their properties are discussed in the scope of an airborne bi-platform passive localization context. Conclusions are drawn regarding the overall localization performance of the system.

关键词： Synchronization Allan variance time deviation TDOA FDOA passive localization USRP (universal software radio peripheral).