Ali Khenchaf

ENSTA Bretagne · Lab-STICC UMR CNRS 6285

Modeling electromagnetic propagation in the maritime environment is a key element in calibrating detection tools, for example in SAR imaging. This article presents a method to compute the propagation above a polluted sea surface. The latter is based on the parabolic wave equation solved with the split-step wavelet method. A hybrid method is also us...

The atmospheric water vapor is commonly monitored from ground Global Navigation Satellite System (GNSS) measurements, by retrieving the tropospheric delay under the Zenith Wet Delay (ZWD) component, linked to the water vapor content in the atmosphere. In recent years, the GNSS ZWD retrieval has been performed on shipborne antennas to gather more at...

Computing the Radar Cross-Section (RCS) of a given object is a topic of major importance for many applications, e.g., target detection and stealth technology. In this context, high-frequency asymptotic methods are widely used. In this article, we derive a Gaussian Beam Summation (GBS) method for both metallic and dielectric targets. The basic idea...

Retrieving the oil-water mixture ratio (M, the proportion of oil in an oil-water mixture) of the marine oil spill is of vital importance for the emergency treatment of oil pollution, which can be achieved by a copolarization ratio (PR) method. In the framework of the PR method, it is assumed that Bragg scattering dominates at moderate incidence ang...

Water vapor is a key variable in meteorology and climate studies. Since the late 90s, Global Navigation Satellite System (GNSS) estimates from ground antennas are commonly used for its description. Indeed, propagation delays are due to the transit of the signal through the atmosphere. The correction of these delays is a crucial step that is needed...

A quantum illumination radar uses quantum entanglement to enhance photodetection sensitivity. The entanglement is quickly destroyed by the decoherence in an environment, although the sensitivity enhancement could survive thanks to quantum correlations beyond the entanglement. These quantum correlations are quantified by the quantum discord. Here, w...

In the context of improving the dimensioning of observation and telecommunication, the characterization of the propagation canal is very important. Thus, accurate models of propagation phenomenona in their environment and above a rough surface (maritime or terrestrial) are of major interest for many applications (such as radar, communications, and...

Along with the rapid development of marine radar, and particularly those carried on aircraft, the detection of small-sized targets which pose an increasing threat has become one of the main areas of interest. However, by considering an observation chain from an aircraft (such as a drone) in a maritime environment, with the aim of detecting and trac...

In the past decades, Bragg scattering has been considered to be an important scattering mechanism of microwave backscattering from sea surfaces. However, as reported in many recent literatures, non-Bragg scattering (which is often attributed to wave breaking) also makes a significant impact on radar scattering, especially for Horizontal–Horizontal...

The two-scale Model (TSM) is broadly employed for studying EM scattering from rough sea surface due to its advantage of simple and practical. However, it suffers from a drawback in the prediction of microwave scattering from sea surface. That is the TSM cannot provide accurate predictions for hh polarized scattering coefficients. To overcome this p...

Wind information on SAR images are essential to characterize a marine environment in offshore or coastal area. More and more applications require high resolution wind field estimation. In this article, classical wind wave direction estimation methods are reviewed as the spectral or gradient approaches. In addition, a way to enhance the spectral met...

In the recent years, multi-constellation and multi-frequency have improved the positioning precision in GNSS applications and significantly expanded the range of applications to new areas and services. However, the use of multiple signals presents advantages as well as disadvantages, since they may contain poor quality signals that negatively impac...

This article is devoted to investigating the microwave scattering mechanisms of oil-free and oil-covered sea surfaces for an incidence angle smaller than 30° in a backscattering configuration. The Elfouhaily spectrum is used to simulate an oil-free sea surface, whereas the Elfouhaily spectrum combined with the Jenkins damping model is applied to th...

We propose in this paper a new method for targets recognition from radar images. To characterize the radar images, we adopt a statistical multivariate modeling using copula in the complex wavelet domain. For the recognition step, we investigate the weighted sparse representation-based classification (WSRC) method. To build the dictionary, the estim...

In this paper, we consider the problem of autonomous task allocation and trajectory planning for a set of UAVs. This is a bi-level problem: the upper-level is a task assignment problem, subjected to UAV capability constraints; the lower-level constructs the detailed trajectory of UAVs, subjected to dynamics, avoidance and dependency constraints. Al...

In this study, the investigation of the electromagnetic scattering by modified targets is presented. A metallic notched plate and disc are considered. Two Gaussian beam (GB) techniques have been applied: GB launching (GBL) and GB summation (GBS). The theoretical formulations of GBL and GBS are established. The simulations of the radar cross-section...

Abstract: An experimental and numerical investigation of the electromagnetic (EM) scattering by reformed radar targets (objects with an aperture) is proposed. The applied Gaussian Beam (GB) methods are: GB Summation (GBS) and GB Launching (GBL). Therefore, the theoretical formulations of GBS and GBL are established. Then, the GBS and GBL techniques...

In this paper, a numerical and experimental investigation of electromagnetic scattering by a notched metallic disc is presented. Gaussian Beam Summation (GBS), Gaussian Beam Launching (GBL), Physical Optic (PO), Physical Theory of Diffraction (PTD) and Method of Moment (MoM) are applied for the simulation of the electromagnetic scattered fields. In...

This paper addresses the estimation of the height of a point scatterer over a sea surface via multipath exploitation for a High Range Resolution radar that is using pulse range compression, such as Synthetic Aperture Radars. We first focus our attention on the physical model, in particular on the specular/diffuse reflection coefficients, this coeff...

Abstract: This paper is devoted to investigating the electromagnetic (EM) backscattering from slick-free and slick-covered sea surfaces at various bands (L-band, C-band, X-band, and Ku-band) by using the second-order small slope approximation (SSA-2) and the measured synthetic aperture radar (SAR) data. It is known that the impact of slick on sea s...

This paper proposes a new target recognition method for inverse synthetic aperture radar (ISAR) images. This method is based on joint statistical modeling of the complex wavelet coefficients for ISAR image characterization and the sparse representation based classification (SRC) for the recognition. To extract features from an ISAR image, we first...

Abstract: The microwave scatterometer is one of the most effective instruments in ocean remote sensing, which urges the need for some theoretical models to accurately estimate the scattering coefficient of the sea surface. For the simulation of the scattering from an ocean surface, the sea spectrum, or its inverse Fourier transform, autocorrelation...

Abstract: The microwave scatterometer is one of the most effective instruments in ocean remotesensing, which urges the need for some theoretical models to accurately estimate the scattering coefficient of the sea surface. For the simulation of the scattering from an ocean surface, the sea spectrum, or its inverse Fourier transform, autocorrelation...

Modern military targets as aircraft are able to perform high maneuvers due to their complex design. This ability of maneuvers includes sudden changes in acceleration and high-G turns that are not achievable from traditional military targets. Moreover, recent military targets generally have a low radar cross-section or low signal-to-noise ratio (SNR...

In this paper, we propose a novel approach to recognize radar targets on inverse synthetic aperture radar (ISAR) and synthetic aperture radar (SAR) images. This approach is based on the multiple salient keypoint descriptors (MSKD) and multitask sparse representation based classification (MSRC). Thus, to characterize the targets in the radar images,...

This paper presents a numerical and experimental study of Radar Cross Section (RCS) of radar targets using Gaussian Beam Summation (GBS) method. The purpose GBS method has several advantages over ray method, mainly on the caustic problem. To evaluate the performance of the chosen method, we started the analysis of the RCS using Gaussian Beam Summat...

Surface wind speed estimation from synthetic aperture radar (SAR) data is principally based on empirical (EP) approaches, e.g., CMOD functions. However, it is necessary and significant to compare radar backscattering modeling based on EP and electromagnetic (EM) approaches for enhancing the understanding of the physical processes between radar sign...

In this paper, we propose a novel approach to recognize radar targets on inverse synthetic aperture radar (ISAR) and synthetic aperture radar (SAR) images. This approach is based on the multiple salient keypoint descriptors (MSKD) and multitask sparse representation based classification (MSRC). Thus, to characterize the targets in the radar images,...

In this paper, we present a novel approach for radar automatic target recognition on inverse synthetic aperture radar (ISAR). This approach is composed by two complementary steps: feature extraction and recognition. For the feature extraction step, we adopt a statistical modeling of the ISAR image in the complex wavelet domain. For doing so, we app...

The objective of this paper is to analyze the effect of the pollutant such as petrol-emulsion on the electromagnetic scattered filed by a maritime surface. Firstly, we investigate the pollutant influence on the maritime surface and physical properties of seawater. Then, we simulate the variation of electromagnetic scattering of the clean maritime s...

Detect and tracking of moving weak targets is a complicated dynamic state estimation problem whose difficulty is increased in case of high clutter conditions or low signal to noise ratio (SNR). In this case, the track-before-detect filter (TBDF) that uses unthresholded measurements considers as an effective method for detecting and tracking a singl...

Synthetic aperture radar (SAR) is one of the favorite tools for earth observation applications, i.e., oceanography, land use mapping, climate change since this device can offer the data at a high spatial resolution and in most meteorological conditions. This is more significant when the data acquired by the Sentinel-1, a new C-band satellite, are e...

This paper aims to present a novel method for automatic target recognition based on synthetic aperture radar (SAR) images. In order to describe a region of interest (target area), we use a saliency attention model. Then, the produced saliency map is used as a mask on SAR image in order to separate the ground target from the background. After that,...

In addition to image processing and neural network, inverting the Geophysical Model Functions (GMFs) is one of the most widely used ways to retrieve oceanic parameters, i.e. surface wind speed, temperature, salinity, etc., from Synthetic Aperture Radar (SAR) data. More exact the description of the GMFs is, more accurately the results are obtained....

Target tracking in the time is a difficult problem of dynamic state estimation; the problem is more complex in a low signal to noise ratio (SNR) or in high clutter conditions. An efficient approach for target detection and tracking under low signal to noise ratio (SNR) conditions is the Track-Before-Detect (TBDF) filter. This paper proposes to use...

The classification of radar emitters in a naval electronic warfare context is a challenging problem. Furthermore, over the last few years, new technologies and the reduction of the fabrication costs have led to an increase in the number of radar. Thus, electronic warfare systems need to improve their capabilities of radar identification. The common...

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 pe...

Dans le présent papier, nous proposons l’étude et l’application d’une nouvelle approche pour l’aide à la reconnaissance automatique de cibles (ATR, pour Automatic Target Recognition) à partir des images à synthèse d’ouverture inverse (ISAR, pour Inverse Synthetic Aperture Radar). Cette approche est composée de deux phases principales. Dans la premi...

This paper deals with the problematic of automatic target recognition (ATR) using Synthetic Aperture Radar (SAR) images. In this work, the Deep Learning (DL) architecture is proposed and applied in order to recognize military vehicles from SAR images. We propose mainly in this work the deep learning algorithms based on convolutional neural network...

The work presented in this paper is part of the filed of automatic recognition of radar targets. Thus, for assistance in target recognition, we propose a new approach to extract efficient feature from synthetic aperture radar (SAR) images. The proposed approach deals with a combination of two feature descriptors obtained from two methods. In the fi...

Ce papier s'intègre bien dans la problématiques générale de la reconnaissance automatique de cibles radar (ATR, pour Automatic Target Recognition) et ceci en s'appuyant sur des images ISAR (Inverse Synthetic Aperture Radar). Dans le travail présenté dans ce papier, nous proposons un nouveau descripteur caractérisant une image Radar (le cas considér...

Sea surface wind is a key parameter in the studies of many oceanic applications, i.e. meteorological forecasting, oil slick observation, ship detection, wind turbine installation recently, etc. Among available wind sources, i.e. in situ measurement, numeric weather models, etc., the retrieval of wind fields from Synthetic Aperture Radar (SAR) data...