La compression d’images embarquée pour les missions spatiales

On-board space instruments produce more and more high amount of data due to the increase in both resolution and number of bits per pixel, not compensated by the reduced swath. Due to the stringent limitations (in terms of mass and power) which apply to on-board equipment, it is essential to reduce to a minimum the on-board sto-rage capacity and the on-board transmission rate needed to fullfill the mission: on-board image compression is a very powerful tool to optimise the resources. The availability, for spaceborne applications, of highly integrated circuits allows to implement on board very sophisticated real-time compression schemes and then to improve the performances of on-board compression. The whole image chain (from the sensor to the on-ground post-processing such as déconvolution and denoising) has to be considered in order to select the compression algorithm and the compression ratio. This article presents the compression algorithms, selected or currently studied, for space missions, and the methods of image quality evaluation.     

Discrimination des modes pour l’étude des discontinuités dans les circuits planaires

The study of the dispersion phenomena of a planar transmission line in boxed structure is very intricate. In this paper we will try to determine the origin of the different modes by varying the geometrical parameters of the structure at a given frequency. We will also study the complex modes and their effects on thee characterisation of the planar discontinuities.     

Potentialités des séquences d’étalement chaotiques pour l’amélioration duTEEB d’un systèmeDS-CDMA asynchrone

The use of chaotic sequences as spectral spreading sequences in a Direct Sequence-Code Division Multiple Access is proposed in this paper. The simulation of the system is performed with the system simulator Omnisys. The chaotic spreading sequences are generated from a non-linear recursive equation. The Bit Error Rate of this system is compared with theBER of the same system using binary Gold sequences. The results show that chaotic sequences can improve performances in terms of allowable number of users.     

Technologies du tatouage pour l’authentification et la protection des images

This paper overviews image watermarking techniques and their integration into protection systems. It is shown how that technology can solve the problems of waveform authentication as well as those related to tracing of digital copies. Image processing techniques and the communication system of watermarking are briefly presented. Some challenges approach to the watermarking field are enumerated in the conclusion.     

Evaluation des performances du réseau en anneau AMBRE pour distribution d’abonnés

ambre is an integrated services digital loop-like network for public local communication. Each communication is a sequence of fixed-length packets separated by fixed-length silences. Performance evaluation is carried through in terms of access-time and transport delays with emphasis on inter packet delay fluctuations.     

Logiciel d’acquisition de données,traitement et aide au tir pour simulation IEM multivoie

Electromagnetic compatibility testing yields a large quantity of data for systematic analysis. An automated data acquisition system has been developed. It is based on standard emp instrumentation which allows a preestablished program to be followed whilst orientating the measurements according to the results obtained. The system is controlled by a computer running interactive programs (multitask windows, scrollable menus, mouse, etc.) which handle the measurement channels, files, displays and process data in addition to providing an aid to firing.     

Sur les méthodes de calcul de l’exposant linéique de propagation et d’impédance caractéristique des câbles aériens et enterrés

The propagation constant of a line or a cable, and its characteristic impedance represent two parameters which are needed in order to calculate the variation as a function of the time of a current induced by an emp.For the aerial lines expressions which take into account the presence of the soil could be developed but the case of the buried conductors is of a more difficult approach. The aim of this study is to present solutions introduced by different authors and to compare them with a calculation method for the propagation constant using iterations, proposed by the authors. If this value is known it is shown that the characteristic impedance calculation of buried cables can be improved by avoiding the necessity to compute with a reasonable precision the impedance of the ground.     

Compression de données brutes et d’images de radar à synthèse d’ouverture

This paper draws a state of the art of synthetic aperture radar (sar) data compression. Both raw data and synthesized image compression have been investigated. Compression of radar raw signal and sar image are considered separately since those two cases are specific. Also, Radar raw/image compression remains different from optical image compression and has to be considered with specific strategies that are adapted to the context.     

Sur une expression des puissances d’une matrice et son application aux réseaux itérés

Annals of Telecommunications - Après une brève introduction, dans unepremière partie, l’auteur donne (I), de lapuissance d’une matrice d’ordre 2, une expression...     

Modélisation des discontinuités d’un objectif radar par des points brillants

In order to study the scattering of a monochromatic electromagnetic wave by a complex radar target, specialists usually modelize the target by a discrete scatterers model. The majority of the scatterers are represented by specular points of reflexion on the surface of the target, but the radar cross section (rcs) is also a function of surface discontinuities. In this article, we develop a method which allows us to replace the discontinuities by groups of point contributors of which the positions and thercs are given. Eventhough thercs are generally functions which decrease as the frequency increases, which can at times be neglected, it can be shown there exists quite frequentlyrcs which are independent of the wavelength. General formulae are given. It is emphasized that the physical optic integral may be used to calculatercs eventhough the conditions of application are not correct. For this reason a number of coefficients including the polarisations are used. The formulae of these coefficients are given. As a result an evaluation of thercs may be simplified, and the same method may be used to study the specular regions and the surface discontinuities.