Local unified models of backscattering from ocean-like surfaces at moderate incidence angles

6 pagesInternational audienceIn the context of electromagnetic wave backscattering from ocean-like surfaces, by using the SSA-1 model, Bourlier et al. proposed a technique to reduce the number of numerical integrations to two for easier numerical implementation. To be consistent with microwave measurements, closed-form expressions of the Fourier coefficients of the backscattering RCS are obtained. For Gaussian statistics, previous work is extended to kernels of unified models expanded up to the order two, like the SSA2 and LCA2

Correlation effect between transmitter and receiver azimuthal directions on the illumination function from a random rough surface

International audienceThe resolution of some problems of electromagnetic scattering from random rough surfaces implies the derivation of the illumination function, especially when the geometrical optics approximation is valid. In current models, the shadowing e ects occurring for both the trans- mitter and the receiver are assumed to be independent of their azimuthal directions. This assumption makes it possible to compute separately the shadowing probabilities in each di- rection. However, if the transmitter and receiver azimuthal directions are close, these proba- bilities become strongly correlated. In such a con guration, the uncorrelation approximation induces an overestimation of the average illumination function up to 10% as well as a discon- tinuity. In this paper, assuming a surface with Gaussian process, this correlation is taken into account. Comparisons of our model with Monte Carlo simulations are made and show a very good agreement, which validates our approach

Electromagnetic Scattering From Two-Scatterers Using the Extended Propagation-Inside-Layer Expansion Method

In this paper, the electromagnetic scattering from two scatterers is analyzed from a rigorous integral formulation solved by the method of moments (MoM). G. Kubick´e has recently developed the E-PILE (Extended Propagation-Inside-Layer Expansion) method to calculate the scattering from an object above a rough surface for a two-dimensional problem. This method allows us to calculate separately and exactly the interactions between the object and the rough surface. The purpose of this paper is to extend the E-PILE method to a three-dimensional problem

Rough surface RCS measurements and simulations using the Physical Optics Approximation

International audienceThe objective of this article is to develop innovative approaches to obtain analytical expressions of the Radar Cross Section (RCS) of perfectly-conducting random rough surfaces under the Physical Optics (PO) approximation. The led approaches take into account the specific geometrical properties of the considered surfaces to calculate their RCS. The objective is to reduce the computing time with respect to the numerical PO technique, which requires two numerical integrations. All developed approaches are validated by comparison with a commercial code (the MLFMM of FEKO), used as a reference, and with measurements performed on three selected rough surfaces samples

A duct mapping method using least squares support vector machines

International audienceThis paper introduces a “refractivity from clutter” (RFC) approach with an inversion method based on a pregenerated database. The RFC method exploits the information contained in the radar sea clutter return to estimate the refractive index profile. Whereas initial efforts are based on algorithms giving a good accuracy involving high computational needs, the present method is based on a learning machine algorithm in order to obtain a real-time system. This paper shows the feasibility of a RFC technique based on the least squares support vector machine inversion method by comparing it to a genetic algorithm on simulated and noise-free data, at 1 and 5 GHz. These data are simulated in the presence of ideal trilinear surface-based ducts. The learning machine is based on a pregenerated database computed using Latin hypercube sampling to improve the efficiency of the learning. The results show that little accuracy is lost compared to a genetic algorithm approach. The computational time of a genetic algorithm is very high, whereas the learning machine approach is real time. The advantage of a real-time RFC system is that it could work on several azimuths in near real time

Caractérisation de films d'huile de la bande X à la bande K, expérimentation en bassin à vagues

This paper depicts an experiment conducted in a wind-wave pool in Brest, France, to characterize oil films when observed at moderate incidence from a X-to-K-band radar. Simultaneous measurements of surface elevation and radar backscattered field were carried out for various sea water surface states and incident angles. From this meaningful dataset (mainly lying in simultaneous acquisitions in X-, Ku-and K-band), an inversion method is proposed to characterize some properties of the oil film: its origin (mineral or biogenic) and its fractional coverage indicator. This process is based on the minimization of the cost function correlating the values given by a physical model of the wave damping ratio and the measured ones. The resulting oil parameters are found in overall good agreement with the three different released oils (two mineral and one biogenic) and it is observed that the fractional filling indicator of the oil slick decreases with increasing the roughness surface state whatever the considered oil.Ce papier décrit une expérimentation menée dans un bassin à vagues à Brest, France. L'objectif est de caractériser les films d'huile observés au moyen d'un système radar à des angles d'incidence modérée de la bande X à la bande K. Des mesures simultanées de l'élévation de la surface et du champ électromagnétique rétro-diffusé furent réalisées pour différents états de surface et divers angles d'incidence. A partir de cette base de données, une méthode d'inversion est proposée pour caractériser plusieurs propriétés du film d'huile: son origine (minérale ou biogénique) ainsi que sa fraction de couverture surfacique. Ce processus repose sur la minimisation d'une fonction coût liant la modélisation physique du coefficient d'atténuation des vagues avec la mesure. Les paramètres estimés sont en accord avec les trois huiles différentes déversées (deux minérales et une biogénique). Il est également observé que la fraction de couverture surfacique de la nappe d'huile décroît avec l'augmentation de la rugosité de surface et ce, quelle que soit l'huile considérée

Improvement of shadowing with iterative physical optics for radiation pattern of mounted antennas

International audienceModeling interactions between antennas and structures is an important challenge for systems carrying antennas such as aircrafts, satellites, frigates. This paper focuses on the electromagnetic field propagated by an antenna interacting with a structure that includes effects of shadowing and multiple reflections. In such a case, several method can be used, and Iterative Physical Optics (IPO) is an asymptotic method based on Physical Optics (PO), which has shown good results in calculation of electromagnetic diffraction in open-ended cavities. In IPO, different techniques can be used to take into account shadowing effects. First method, classically used, is a geometrical way of considering shadowing, based on ray bouncing. A more recent method uses a physical approach, based on shadow radiation (around forward direction) with PO approximation. The idea of this paper is to use IPO method to determine electromagnetic field from a structure including an antenna on a large complex platform, comparing different ways of considering shadowing effect

Microwave Non‐Destructive Testing of Non‐Dispersive and Dispersive Media Using High‐Resolution Methods

This chapter discusses the principle and application of two model‐based algorithms for processing non‐dispersive and dispersive ground penetrating radar (GPR) data over layered medium under monostatic antenna configuration. Both algorithms have been selected for their super‐time resolution capability and reduced computational burden; they allow GPR to measure a layer thickness smaller than the fraction of the dominant wavelength. For non‐dispersive data, the ESPRIT algorithm is generalized to handle different kinds of data models encountered in experiments and in the literature. For dispersive data, the proposed adaptation of the MPM algorithm allows recovering the full‐time resolution and jointly estimating the time delays and quality factors of a layered medium with reduced bias. Both processing techniques are applied to probe‐layered roadways for NDT&E purposes

Radar Propagation and Scattering in a Complex Maritime Environment: Modeling and Simulation from MatLab

Co-publisher: Elsevier - ScienceDirectInternational audienceThis book focuses on the modeling of radar electromagnetic wave propagation and scattering in complex maritime environments. The book is intended for graduate students and engineers as well as for researchers who encounter such problems.Together with the relevant MatLab® codes, which are also provided, this book contains five chapters. The first chapter presents fast algorithms, based on the Method of Moments (MoM), to calculate the scattering from one-dimensional rough surfaces. Chapter 2 addresses asymptotic scattering models and their validation from the rigorous methods developed in Chapter 1. The final three chapters focus on three main applications: airborne and low-grazing angle SHF (typically from 1 to 20 GHz) propagation from sea surfaces, and HF (typically from 1 to 30 MHz) propagation above the Earth.The interest of this book is that it investigates both of the derivations of the asymptotic formulations and compares them with fast rigorous methods, based on the MoM, to access their validity domain.All the MatLab codes used to make the figures are provided