Download or read book Scattering and Propagation in Random Media written by North Atlantic Treaty Organization. Advisory Group for Aerospace Research and Development. Electromagnetic Wave Propagation Panel. Specialists' Meeting and published by . This book was released on 1988 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt: The topic of scattering and propagation in random media is one that has implications for the design, development and operation of most military systems that radiate energy as a means of accomplishing their funtion. Primary emphasis is on scattering and transmission in the atmosphere; however, other related random medium effects are not excluded. Modern methods of characterizing random media, mathematical methods and their applicability, effects on electromagnetic waves and the interpretation of these effects to specific system applications are described. The region of the spectrum considered is essentially unlimited and ranges from very long waves to optics. The performance of existing surveillance communication and navigation systems as well as the design of future systems is influenced by the propagation of energy via random media. An understanding of the nature of the medium and its impact on system design and performance is essential to the NATO community.

Download or read book Etude d un nouveau concept d analyse de front d onde en plan focal appliqu l optique adaptative en astronomie written by Cédric Plantet and published by . This book was released on 2014 with total page 213 pages. Available in PDF, EPUB and Kindle. Book excerpt: L'avènement des Extremely Large Telescopes (ELT) est imminent. Cette nouvelle génération de télescopes ouvrira la voie vers des observations astronomiques toujours plus fines. Les futurs instruments nécessitent des optiques adaptatives de plus en plus sophistiquées pour corriger les effets de la turbulence et atteindre les performances requises. L'analyse de front d'onde est un élément fondamental de l'optique adaptative. Les analyseurs requièrent un flux relativement élevé pour être efficaces, notamment lors de l'estimation de hauts ordres, qui sont nécessaires pour obtenir une bonne correction. Comme le ciel est pauvre en étoiles brillantes, on utilise souvent des étoiles laser, produites par excitation d'un volume de sodium dans la haute atmosphère. Malheureusement, on ne peut pas estimer correctement un tip/tilt avec ces étoiles artificielles. De plus, le focus mesuré est biaisé à cause de l'instabilité en altitude de la couche de sodium. La mesure de ces trois aberrations doit donc pouvoir être faite sur une étoile naturelle de très faible luminosité. On peut alors se demander quelle stratégie adopter pour l'analyse des bas ordres à faible flux. De manière plus générale, les techniques d'analyse de front d'onde sont en pleine évolution pour répondre aux nouveaux besoins de l'optique adaptative. Il est donc important de comparer les stratégies d'analyse en terme de sensibilité et de dynamique. La thèse s'appuie sur un nouveau concept d'analyseur de surface d'onde : LIFT (LInearized Focal-plane Technique). Cet analyseur permettra d'estimer le tip/tilt et le focus sur une étoile naturelle faible, afin de compléter l'analyse faite sur les étoiles lasers, de façon plus efficace qu'avec les moyens actuels. Le premier but de la thèse est d'optimiser et de valider LIFT expérimentalement. Pour cela, j'ai d'abord étudié les propriétés de convergence de l'algorithme et la propagation du bruit afin de déterminer les paramètres optimaux. J'ai ensuite testé le concept de LIFT en laboratoire sur des phases statiques, puis sur le ciel grâce au système d'optique adaptative du télescope Gemini Sud, GeMS. La linéarité de l'estimation malgré la présence de hauts ordres résiduels, dus à la correction imparfaite de l'optique adaptative, a été validée en boucle ouverte, et nous pouvons maintenant envisager une validation finale en intégrant LIFT dans une boucle fermée. Dans un deuxième temps, j'ai étudié la propagation du bruit dans un analyseur dérivé de LIFT, le Shack-Hartmann LIFTé. Cet analyseur divise la pupille à l'aide de micro-lentilles astigmatiques, et une estimation par LIFT est faite dans chaque sous-pupille. Il permettra une estimation de hauts ordres plus précise qu'avec un Shack-Hartmann classique. Le dernier objectif est de comparer les analyseurs existants, en termes de propagation de bruit, pour l'estimation sur étoile naturelle des bas ordres d'une part, cas d'application de LIFT, et des hauts ordres d'autre part, dans le cas d'une optique adaptative extrême par exemple. Cette étude permet de motiver l'utilisation de LIFT et du Shack-Hartmann LIFTé dans des systèmes d'optique adaptative.

Download or read book Analyse de front d onde en plan focal written by Isabelle Mocoeur and published by . This book was released on 2008 with total page 255 pages. Available in PDF, EPUB and Kindle. Book excerpt: Optical interferometry allows to reach the resolution of a large instrument by coupling several sub-apertures of lower diameter. However, this method requires a very accurate control of the optical paths, especially the differential aberrations between the apertures (so-called cophasing operation). In this context, focal-plane sensors as phase retrieval or phase diversity techniques (based respectively on the acquisition of one or at least two images aberrated with a known phase) appears to be an advantageous solution with a very simple opto-mechanical setup. However, these estimators are iterative and consequently potentially time-consuming. In this manuscript, we propose new algorithms which are well-suited for real-time cophasing on extended objects. We demonstrate that a quadratic criterion can be derived, which allows to express the solution under a simple analytical form. We also show that the expression of this new criterion can be obtained in the case of small phase perturbations considering a linear expression of the optical transfer function. The performance we obtained on simulated data demonstrates the possibility of using the analytic algorithms in a closed-loop system at low fluxes and restoring the observed object as well. Experimental validations of both iterative and analytic estimators for various projects confirm that the focal plane approach now can be used for the cophasing of complex phased-array systems.

Download or read book Canadian Journal of Physics written by and published by . This book was released on 1961 with total page 1016 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book D finition et caract risation d un nouvel analyseur de front d onde plan focal temps r el written by Bertrand Denolle and published by . This book was released on 2013 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: Résumé anglais

Download or read book Analyse de front d onde pour les optiques adaptatives de nouvelle g n ration written by Magalie Nicolle and published by . This book was released on 2006 with total page 363 pages. Available in PDF, EPUB and Kindle. Book excerpt: Several points restrict the efficiency of the wavefront analysis of actual adaptive optics (AO) systems. The mains ones are the measurement noise and the anisoplanatism. Together, they reduce to a few percents the sky coverage of the instruments assisted by AO. For this reason, rising generation of AO systems aims at the very high performance (implying in particular low measurement noise) and/or the widening of the corrected field. For these wide field AO systems, it is essential to use several directions of analysis. The wavefront analysis problem is then articulated around three items : the available guides stars, the considered wavefront sensing concept and quality of the wavefront sensors measurements. The purpose of this PhD thesis is to study each one of these three aspects. Hence a redefinition of the concept of sky coverage is proposed for wide field AO. The definition suggested here takes into account the number of guide stars and their magnitude, but also the fraction of the scientific field that is really covered, the considered wavefront sensing concept and the expected performance of the instrument. Concerning the wavefront sensing concepts, a comparative study of the Star Oriented and Layer Oriented concepts is presented and an optimization is proposed for each one, leading to very close performance. Finally, a comparison of different wavefront slope estimators is proposed for the Shack-Hartmann wavefront sensor. In particular, a weighted center of gravity estimator is studied, that offers a good robustness to noise and good properties of linearity. This last study is usefull as well for wide field AO as for very high performance AO.

Download or read book Analyse de front d onde en plan focal written by Enguerran Delavaquerie and published by . This book was released on 2010 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: Les instruments optiques à pupilles multiples permettent d'obtenir de très hautes résolutions angulaires en mettant en réseau des télescopes, ou en utilisant des surfaces réfléchissantes segmentées. Pour fournir une résolution optimale, les sous-pupilles de ces instruments doivent être cophasées, c'est-à-dire alignées en piston et basculement, à l'aide 'un capteur de front d'onde. Placé au foyer de l'instrument, le capteur peut mesurer les aberrations instrumentales perturbant les observations, en utilisant des techniques d'analyse de l'image telles que le phase retrieval et de la diversité de phase. Cependant, ces estimateurs ont l'inconvénient d'être itératifs et donc potentiellement coûteux en temps de calcul. Sur la base d'un nouveau formalisme décrivant de manière simplifiée le modèle de formation d'image, de nombreux algorithmes peuvent être dérivés pour la résolution du problème inverse. Ces différents algorithmes peuvent prendre en compte l'extension de l'objet, la géométrie de la pupille, le nombre et la nature des plans de mesure, ... Dans une première étape, les travaux portent sur la mesure des pistons différentiels e,tre les sous-pupilles, principaux contributeurs à l'erreur d'alignement, dans le cadre d'observation d'un point source ou d'un objet étendu. Plusieurs estimateurs, analytiques et linéaires, ont été dérivés. La validation des estimateurs s'est déroulée en deux étapes. Des simulations numériques ont montré, pour certaines configurations pupillaires, un comportement très proche à celui des estimateurs itératifs précédents. Des mesures expérimentales sur un miroir segmenté confirment le bon comportement des algorithmes dans des conditions réelles. Ces premiers résultats confirment la validité de l'approche suivie.

Download or read book Physics in Canada written by and published by . This book was released on 1975 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Journal de physique written by and published by . This book was released on 2002 with total page 1008 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Genius of Architecture Or The Analogy of that Art with Our Sensations written by Nicolas Le Camus de Mézières and published by Getty Publications. This book was released on 1992 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt: This series offers a range of heretofore unavailable writings in English translation on the subjects of art, architecture, and aesthetics. Camus's description of the French hotel argues that architecture should please the senses and the mind.

Download or read book Journal of the Institution of Engineers India written by and published by . This book was released on 1970 with total page 262 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Integral Fourier Operators written by Michèle Audin and published by Universitätsverlag Potsdam. This book was released on 2018-04-17 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume of contributions based on lectures delivered at a school on Fourier Integral Operators held in Ouagadougou, Burkina Faso, 14–26 September 2015, provides an introduction to Fourier Integral Operators (FIO) for a readership of Master and PhD students as well as any interested layperson. Considering the wide spectrum of their applications and the richness of the mathematical tools they involve, FIOs lie the cross-road of many a field. This volume offers the necessary background, whether analytic or geometric, to get acquainted with FIOs, complemented by more advanced material presenting various aspects of active research in that area.

Download or read book Lenses and Waves written by Fokko Jan Dijksterhuis and published by Springer Science & Business Media. This book was released on 2006-01-20 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt: In 1690, Christiaan Huygens (1629-1695) published Traité de la Lumière, containing his renowned wave theory of light. It is considered a landmark in seventeenth-century science, for the way Huygens mathematized the corpuscular nature of light and his probabilistic conception of natural knowledge. This book discusses the development of Huygens' wave theory, reconstructing the winding road that eventually led to Traité de la Lumière. For the first time, the full range of manuscript sources is taken into account. In addition, the development of Huygens' thinking on the nature of light is put in the context of his optics as a whole, which was dominated by his lifelong pursuit of theoretical and practical dioptrics. In so doing, this book offers the first account of the development of Huygens' mathematical analysis of lenses and telescopes and its significance for the origin of the wave theory of light. As Huygens applied his mathematical proficiency to practical issues pertaining to telescopes – including trying to design a perfect telescope by means of mathematical theory – his dioptrics is significant for our understanding of seventeenth-century relations between theory and practice. With this full account of Huygens' optics, this book sheds new light on the history of seventeenth-century optics and the rise of the new mathematical sciences, as well as Huygens' oeuvre as a whole. Students of the history of optics, of early mathematical physics, and the Scientific Revolution, will find this book enlightening.

Download or read book Acta electronica written by and published by . This book was released on 1968 with total page 510 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Diagnosing and Changing Organizational Culture written by Kim S. Cameron and published by John Wiley & Sons. This book was released on 2011-01-07 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt: Diagnosing and Changing Organizational Culture provides a framework, a sense-making tool, a set of systematic steps, and a methodology for helping managers and their organizations carefully analyze and alter their fundamental culture. Authors, Cameron and Quinn focus on the methods and mechanisms that are available to help managers and change agents transform the most fundamental elements of their organizations. The authors also provide instruments to help individuals guide the change process at the most basic level—culture. Diagnosing and Changing Organizational Culture offers a systematic strategy for internal or external change agents to facilitate foundational change that in turn makes it possible to support and supplement other kinds of change initiatives.

Download or read book Diffractive Optics for Virtual Reality Displays written by Tapani Levola and published by . This book was released on 2005 with total page 107 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Women and Music in Sixteenth Century Ferrara written by Laurie Stras and published by Cambridge University Press. This book was released on 2018-09-27 with total page 417 pages. Available in PDF, EPUB and Kindle. Book excerpt: Rethinks and retells the history of music in sixteenth-century Ferrara, putting women, of the court and convent, at the narrative centre.