No description available.

No description available.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / In this paper, we present the recent results of theoretical development and software implementation of a complete collection of high-performance image reconstruction algorithms designed for high-resolution imaging for various data acquisition configurations.

Dans la situation d’un radar monostatique la configuration diédrique présente l’avantage de renvoyer un signal fort grâce au mécanisme de double rebond. De plus, il s’agit d’une configuration omniprésente par exemple en zone urbaine, avec des structures rue-bâtiment, ou en forêt, avec des structures de type sol-arbre. Les signaux rétrodiffusés sont donc liés à ces structures, plus précisément aux matériaux les composant, via leurs permittivités diélectriques. Retrouver ces permittivités depuis la mesure des champs rétrodiffusés permettrait l’identification des matériaux de la structure diédrique. Ceci mène à des applications telles que la détection de défauts dans la structure, l’estimation de la teneur en eau des sols ou du béton, ou in fine à des thématiques de classification, pour des objets dans des images radar par exemple, ou de détection de changement. En modélisant le mécanisme de double rebond lié à la structure de dièdre par deux réflexions successives via les coefficients de Fresnel, trois méthodes d’inversion des permittivités ont été mises en place au cours de la thèse. La première, analytique, utilise à un angle d’incidence donné la mesure des champs copolarisés. Les deux autres méthodes, alliant une partie analytique et une partie numérique, nécessitent la mesure, du ratio polarimétrique pour l’une, du champ horizontal pour l’autre, effectuée à deux angles d’incidence différents. Ces méthodes ont été validées numériquement à l’aide de la méthode d’Optique Géométrique fournie par le logiciel FEKO. Des mesures en chambre anéchoique ont été effectuées afin de valider ces méthodes. De même une mesure in-situ a été effectuée sur un dièdre en béton formé par un angle entre deux murs. / For a monostatic radar, the dihedral arrangementexhibits a strong response compare tobare surface. This phenomenon can be seen in radarimages of urban areas or forestry as building andstreets and trunks and ground are forming such structures.This signature can be modelled with the doublebounce equation as a cascade of Fresnel reflectioncoefficients. These coefficients depend on the permittivitiesof the structures. Finding these permittivitiesfrom the backscattered fields may allowed to identifythe materials involved in the dihedral. Thereforethiscan be applied for default detection, moisture retrievaland classification topics for instance.By modelling the double bounce scattering with Fresnelcoefficients, three methods have been developedto retrieve these permittivities. The first one uses asingle incidence angle and the measurements of copolarisedfields. The last two methods need the measurementof the copolarised fields ratio or of the horizontalelectric field alone at two different incidenceangles. All these methods have been validated, firstnumerically using FEKO RL-GO method, then experimentally,with measurements in anechoic chamber. Atlast, in-situ measurements have been performed on awall corner made of concrete to assess the methodon a real case.

The aim of this thesis is to estimate parameters of the moving target using different radar configurations. First the Doppler effect and the time delay of the received signal is examined. The investigation of these phenomenons is made for radial and non-radial movement of simple monostatic radar configuration and after that for the bistatic and multistatic MIMO configuration. The ambiguity function is presented for all these configurations. The ambiguity function is then used to estimate target parameters from the received signal. The received signal model and ambiguity function for the monostatic radar configuration is developed using Matlab software. Finally the practical use of these implementations is presented and compared.

I takt med att ubåtarna blir allt tystare och svårare att detektera ställs allt högre krav på de sensorer som utvecklas för hålla jämna steg med denna utveckling. Redan under 80-talet kunde man konstatera att ubåtarna hade blivit så tysta att passiv detektering inte räckte till varför intresset istället riktades mot primärt aktiva system. Aktiv sändning medför sina egna nackdelar och tillsammans med de tekniker som utvecklats för att dämpa ekona från en ubåt gör att inte ens en aktiv, monostatisk sonar alltid ger tillfredsställande resultat. Till Försvarsmaktens nya medeltunga helikopter HKP14 har ett nytt sonarsystem införskaffats med möjlighet till fusionerad signalbehandling (s.k. multistatisk sonar) av signaler mottagna från flera olika mottagare såsom t.ex. sonarbojar.   Undersökningen syftar till att belysa vilka fördelar som kan erhållas vid helikopterbaserad, multistatisk ubåtsjakt och visar med ett antal räkneexempel bland annat att en större räckvidd och därmed även ett större detekteringsområde kan förväntas i en multistatisk konfiguration. Beräkningarna är gjorda med utgångspunkt i Uricks sonarekvationer men då faktorer såsom reverberation och kanalutbredning har avgränsats bort är det osäkert hur väl dessa resultat skulle stämma överens med en fältstudie. Utifrån de typfall som har undersökts visar emellertid studien på att de teoretiska fördelarna med ett multistatiskt system är tydliga och att dessa rent logiskt i viss utsträckning även borde gälla i praktiken. / The fact that submarines are becoming more silent and therefore harder to detect has led to an ever-increasing demand for more sensitive and sophisticated sensors to keep up with this development. As early as the 1980s it became obvious that submarines had become so silent that passive detection was not enough and the focus shifted toward active systems instead. Active transmission has its own disadvantages, and new techniques to silence submarines and reduce their acoustic signature even further have led to a situation where not even active, monostatic sonar always produces a satisfactory result. Along with the new medium sized helicopter (NH90), the Swedish Armed Forces have purchased a new sonar system that allows fused signal processing, using signals received by different receivers, such as sonobuoys. The aim of the study is to show what advantages can be gained from helicopter-based multistatic anti-submarine warfare and to show, by a number of arithmetic examples, that greater detection ranges and thus greater detection areas can be expected from a multistatic configuration. The examples are based on Urick’s sonar equations, but since factors such as reverberation and channel propagation of sound have been excluded from the study, it is uncertain how these results would compare to a field study. However, the study clearly shows the theoretical advantages of a multistatic system and that, on the basis of simple logic, these results should be feasible, to some extent, in practice.

No description available.

This project revolves around a monostatic time of flight LiDAR, monostatic meaning that the emitted light and the incoming light are collocated and LiDAR being an acronym for light detection and ranging. The goal here is to explore and understand the principles of the LiDAR whilst also finding its advantages and shortcomings. One expected shortcoming is that of the effects of light scattering of the laser. To mitigate these effects a short laser pulse is desired without compromising on the power output. In order to reduce the pulse width the electronics of the LiDAR needed to be understood and two approaches emerged. The first revolved around simplifying the electronic schematics of the LiDAR to the point it could be described as a simple RLC-circuit and solving for the current analytically. The other approach was to simulate it using the simulation software LTspice. The results from the analytical approach and the LTspice simulation showed clear ways of how the pulse width could be decreased by altering the onboard resistance, inductance and capacitance. The easiest alternative was to simply reduce the capacitance, however this resulted in a lower power output. But these effects could be mitigated by simply increasing the applied voltage. However it was also discovered that the analytical and LTspice simulations were not entirely correct in their attempts to simulate the real behavior of the laser drive boards within the LiDAR. To study the effects of the scattering two theories were studied, namely Rayleigh and Mie scattering. The influence of Rayleigh scattering was quickly determined to be negligible but the Mie scattering results showed that it will definitely affect the LiDAR, even though the Mie scattering influence was extremely over exaggerated.