This thesis treats the optical properties of mixed mineral dust and biomass burning aerosol in the thermal infrared (TIR) based on Fourier Transform infrared spectrometer (FTIR) measurements and radiative transfer simulations. The measurements were part of the Saharan Mineral Dust Experiment 2 (SAMUM-2) conducted from January to February 2008 at Praia, Cape Verde. The large amount of different instruments co-located at the main field site during the campaign resulted in a unique dataset comprising in-situ information and remote sensing data perfectly suited for column closure studies. The ultimate goal of this work is to investigate the consistency of microphysical and TIR remote sensing data. This is achieved by reproducing the measured radiances at top and bottom of the atmosphere (TOA, BOA) with a radiative transfer model, which assimilates the microphysical aerosol information gathered during SAMUM-2. The first part of the thesis describes several experimental efforts, including a novel calibration method and a drift correction algorithm for the ground-based FTIR instrument operated within the scope of SAMUM-2 by the author. The second part introduces the concurrent radiative transfer library PIRATES, which has been developed in the framework of this thesis for the analysis of TIR aerosol optical properties. The third and final part of the treatise compares measured and simulated spectra for various typical scenarios encountered during SAMUM-2. It is demonstrated in three case studies, that measured radiances in the TIR atmospheric window region (8-12 µm) can be reproduced at BOA and TOA by radiative transfer simulations assuming spheroidal model particles. Moreover, spherical particles are shown to be an inadequate model for mineral dust aerosol in this spectral region unless the aerosol optical depth is small.

Le collisionneur SuperKEKB, dédié à l'expérience Belle II, prévoit une très haute luminosité, inégalée à ce jour. Son objectif est de fournir une luminosité instantanée de 8x10³⁵ cm⁻²s⁻¹ en mettant en collision des faisceaux minuscules au point d'interaction (IP) sur la base du schéma "nano-beam". Par conséquent, un excellent contrôle de l'orbite du faisceau à l’IP est nécessaire pour assurer un recouvrement géométrique optimal entre les deux faisceaux en collision, et ainsi maximiser la luminosité. Dans ce cadre, cette thèse présente le développement et l'implémentation d'un système de monitoring rapide de la luminosité de SuperKEKB basé sur des détecteurs en diamant sCVD. Pour atteindre une précision relative aussi élevée et couvrir une gamme dynamique de luminosité élevée, le processus de diffusion Bhabha radiatif à très petit angle est utilisé, dont la section efficace d’interaction est très importante et relativement bien connue. Des détecteurs diamant sCVD, dont le signal est rapide et qui ont une bonne tolérance au rayonnement, sont utilisés pour détecter les particules chargées dans les gerbes électromagnétiques induites par l’interaction entre les particules Bhabha diffusées et perdues dans le tube à vide du faisceau, et dans les autres matériaux, en particulier un radiateur, à des emplacements choisis spécialement en aval de l'IP, dans les deux anneaux LER et HER. Une simulation de bout en bout du système d'asservissement de l'orbite du faisceau à l'IP basé sur notre signal de luminosité rapide et précis a été réalisé, qui comprend: une estimation du signal du détecteur de diamant sCVD, basé sur des mesures de laboratoire à l'aide d'une source radioactive, la construction de séquences de signal représentative de SuperKEKB comprenant les bruits de fond à un seul faisceau et les particules diffusées par le processus Bhabha, un traitement du signal de luminosité, et la simulation de l'asservissement de l'orbite. Il a été possible de vérifier la faisabilité de ce système pour maintenir la très haute luminosité de SuperKEKB en présence des mouvements du sol et a de déterminer la précision relative du signal de luminosité rapide qu'il est possible d'obtenir toutes les 1 ms. Au cours des phases de mise en service de SuperKEKB, la phase 2 et le début de la phase 3, notre moniteur de luminosité rapide basé sur des détecteurs en diamant sCVD a été installé et utilisé avec succès. Les processus de perte de faisceau, principalement ceux provenant des processus de Bremsstrahlung et de Touschek, ont été étudiés en détail et, par rapport à la simulation, un bon accord a été trouvé. Lors de la mise en service de la collision, des signaux de luminosité intégrés toutes les secondes étaient fournis en continu pour le réglage des paramètres des faisceaux à l'IP. En outre, un signal de luminosité intégré toutes les 1 ms avec la précision relative attendue a également été fourni et utilisé comme entrée du système d'asservissement de l'orbite à l'IP, notamment pour des premiers tests conduits avec succès avec des décalages de faisceau horizontaux introduits volontairement. Davantage de tests de ce système d'asservissement sont attendus pour assurer son bon fonctionnement en continu à l'avenir. Cette thèse présente le développement et l’application d’un système de surveillance rapide de la luminosité basé sur les détecteurs de sCVD diamant de SuperKEKB. / SuperKEKB is at the foremost frontier of high luminosity e⁺e⁻ colliders, dedicated to the Belle-II experiment. It aims to provide an instantaneous luminosity of 8x10³⁵ by involving extremely tiny beams colliding at the Interaction Point (IP) based on the "nano-beam scheme". Therefore, excellent control of its beam orbit at the IP is required to ensure the optimum geometrical overlap between the two colliding beams, and thereby maximize the luminosity. Besides, effective instrumentation to diagnose the behavior of the beam at the IP and possible beam interactions between bunches along the train are also quite essential during the long and rather difficult process of machine tuning towards the nominal beam parameters. This thesis presents the development and application of a fast luminosity monitoring system based on sCVD diamond detectors at SuperKEKB, including: (1),train integrated luminosity signals every 1 ms which will be used as input to the dithering orbit feedback system, its relative precision is expected to be better than 1% when luminosity reaches 10³⁴ (2), sensitive train integrated luminosity signals over a large luminosity dynamic range every 1 s which will be sent to the SuperKEKB control room as immediate observable for machine collision tuning, and (3) bunch integrated luminosity signals every 1 s with sufficient relative precision to monitor the collision performance for each single bunch. To achieve such high relative precision and cover a large luminosity dynamic range, the radiative Bhabha process events at vanishing scattering angle will be measured, whose interaction cross-section is quite large and reasonably well known. The sCVD diamond detectors, which have fast signal formation and good radiation tolerance, were used to detect the charged particles in the secondary showers induced by the interaction between the lost Bhabha scattered particles and the beam pipe and specific radiator materials at carefully chosen locations downstream of the IP in both the LER and HER. A start-to-end simulation was performed on the dithering orbit feedback system using fast, precise luminosity signal as input, which includes: sCVD diamond detector signal estimation based on laboratory measurements with a radioactive source, signal sequence construction at SuperKEKB including single beam backgrounds and Bhabha scattered particles, luminosity signal procession, dithering orbit feedback simulation. It enabled verifying the feasibility of this system to maintain very high luminosity in the presence of ground motion, in particular it determined the relative precision of the fast luminosity signal every 1 ms. Besides, the radiation damage of the sCVD diamond detectors in the LER was also estimated based on a FLUKA simulation and applying the NIEL hypothesis. During the Phase-2 and early Phase-3 commissioning periods of SuperKEKB, our fast luminosity monitor based on sCVD diamond detectors was installed and operated successfully. Single beam loss processes, mainly Bremsstrahlung and Touschek, were studied in detail and compared with the simulation, showing good agreement. During the collision commissioning, train and bunch integrated luminosity signals every 1 s were provided for machine tuning. e.g. the vertical beam sizes were determined with the vertical offset scan technique based on our luminosity signals, both the average and for the individual bunches, which is very important and useful for the collision and IP local optics tuning during the long and rather difficult process of SuperKEKB machine tuning towards the nominal beam parameters. Besides, a train integrated luminosity signal every 1 ms with the expected relative precision was also provided and used as input to the dithering orbit feedback system for its first successful tests with deliberately introduced horizontal beam-beam offsets. More tests on the dithering orbit feedback system are expected to ensure its future continuous operation.

No description available.

Two classes of carbon nanomaterials—carbon nanotubes and graphene—have promoted the advancement of nanoelectronics, quantum computing, chemical sensing and storage, thermal management, and optoelectronic components. Studies of the thermal radiative properties of carbon nanotube thin film arrays and simple graphene hybrid structures reveal some of the most exciting characteristic electromagnetic interactions of an unusual sort of material, called hyperbolic metamaterials. The features and results on these materials in the context of both far-field and near-field radiation are presented in this dissertation. Due to the optically dark nature of pyrolytic carbon in the wavelength range from visible to infrared, it has been suggested vertically aligned carbon nanotube (VACNT) coatings may serve as effective radiative absorbers. The spectral optical constants of VACNT are modeled using the effective medium theory (EMT), which is based on the anisotropic permittivity components of graphite. The effects of other EMT parameters such as volume filling ratio and local filament alignment factor are explored. Low reflectance and high absorptance are observed up to the far-infrared and wide range of oblique incidence angles. The radiative properties of tilt-aligned carbon nanotube (TACNT) thin films are illustrated. Energy streamlines by tracing the Poynting vectors are used to show a self-collimation effect within the TACNT thin films, meaning infrared light can be transmitted along the axes of CNT filaments. Graphene, a single layer sheet of carbon atoms, produces variable conductance in the terahertz frequency regime by tailoring the applied voltage gating or doping. Periodically embedding between dielectric spacers, the substitution of graphene provides low radiative attenuation compared to traditional metal-dielectric multilayers. The hyperbolic nature, namely negative angle of refraction, is tested on the graphene-dielectric multilayers imposed with varying levels of doping. EMT should be valid for graphene-dielectric multilayers due to the nanometers-thick layers compared to the characteristic wavelength of infrared light. For metal- or semiconductor-dielectric multilayers with thicker or lossier layers, EMT may not hold. The validity of EMT for these multilayers is better understood by comparing against the radiative properties determined by layered medium optics. When bodies of different temperatures are separated by a nanometers-size vacuum gap, thermal radiation is enhanced several-fold over that of blackbodies. This phenomenon can be used to develop more efficient thermophotovoltaic devices. Due to their hyperbolic nature, VACNT and graphite are demonstrated to further increase evanescent wave tunneling. The heat flux between these materials separated by vacuum gaps smaller than a micron is vastly improved over traditional semiconductor materials. A hybrid structure composed of VACNT substrates covered by doped graphene is analyzed and is shown to further improve the heat flux, due to the surface plasmon polariton coupling between the graphene sheets.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: 138La is a very long-lived and low abundant p-isotope. Most p-nuclei with Z > 54 are thought to be produced through photodisintegration of s- and r-process seed nuclei. However, this p-process cannot satisfactorily explain the observed abundance of 138La, and more exotic processes, such as ve + 138Ba → 138La + e− have to be considered. This v-process can reproduce the observed solar abundance of 138La, but the significance of the p-process cannot be ruled out due to very high uncertainties in its predicted reaction rates. These errors have been discussed to be mainly due to the unavailability of the experimental nuclear level densities and radiative strength functions of 138,139La, which are critical ingredients for astrophysical reaction rate calculations based on the Hauser-Feshbach approach. Thus, nuclear physics measurements are necessary to place the nuclear properties on a strong footing, in order to make statements regarding the importance of p- and v-processes. In this research project the experimental nuclear level densities and radiative strength functions of 138,139La were measured below the neutron thresholds. From this new experimental data, the Maxwellian averaged cross sections for the 137La(n, y) and 138La(n, y) reactions, at the p-process temperature of 2.5⇥109 K, were computed with the TALYS code. Using these reaction rates the nucleosynthesis calculations in the O/Ne-rich layers of Type II supernovae were performed. The results imply that the standard p-process still under-produces 138La, which puts the v-process on a very strong footing as the main production process for 138La. / AFRIKAANSE OPSOMMING: 138La is ’n p-isotoop met ’n baie lang halfleeftyd. Daar word tans vermoed dat p-nukiede met Z > 54 geproduseer word deur fotodisintegrasie van sen r-proses saadnukliede. Nogtans verklaar hierdie p-proses die waargenome natuurlike voorkoms van 138La nie behoorlik nie, en meer eksotiese prosesse soos byvoorbeeld ve+ 138Ba → 138La + e− moet in aanmerking geneem word. Hierdie v-proses kan die waargenome natuurlike voorkoms van 138La verklaar, maar die belangrikheid van die p-proses kan nie afgewys word nie weens die onsekerheid in die voorspelde reaksie snelheid. Sodanige onsekerhede word bespreek en word hoofsaaklik toegeskryf aan die gebrek aan eksperimentele vlakdigthede en stralings sterkefunksies van die kerne 138,139La, wat van kritiese belang is vir berekeninge van astrofisiese reaksie snelhede gebaseer op die Hauser-Feshbach benadering. Kernfisiese metings is derhalwe noodsaaklik om die eienskappe van kerne op ’n stewige grondslag te plaas sodat uitlatings gemaak kan word omtrent die belangrikheid van p- en v-prosesse. In hierdie esperimentele navorsingsprojek is die kern vlakdigthede en stralings sterkefunksies van 138,139La onder die neutron reaksiedrumpels gemeet. Die nuwe gemete data maak dit moontlik om die Maxwell-gemiddelde kansvlakke vir die 137La(n, y) en 138La(n, y) reaksies by ’n p-proses temperatuur van 2.5 x 109 K met die TALYS program te bereken. Hierdie reaksie snelhede is daarna gebruik om berekeninge van elementvorming in die O/Ne-ryke lae van Tipe-II supernovas te maak. Die resultate wys uit dat die stadaard p-proses nie genoegsame 138La produseer nie, wat derhalwe die v-proses op ’n baie stewige grondslag plaas as die hoof produksie proses vir 138La.

The development and application of new cloud retrieval methods from ground–based and airborne measurements of spectral radiance fields above heteorogeneous surfaces is introduced. The potential of imaging spectrometers in remote–sensing applications is evaluated. The analyzed spectral radiance fields were measured during two international field campaigns in the visible wavelength range (400–970 nm) with high spatial (<10m) resolution. From ground–based measurements, high ice clouds were observed and from airborne measurements Arctic stratus. From the measurements, cloud optical thickness is retrieved with high spatial resolution and the horizontal cloud inhomogeneities are investigated. Depending on the measurement configuration, different uncertainties arise for the retrieval of the cloud optical thickness. A reduction of those uncertainties is derived by a specification of the ice crystal shape to improve the retrieval of the optical thickness of high ice clouds. The ice crystal shape is obtained independently from the angular information of the scattering phase function features, imprinted in the radiance fields. A performed sensitivity study reveals uncertainties of up to 90%, when neglecting this information and applying a wrong crystal shape to the retrieval. For remote-sensing of Arctic stratus, the highly variable surface albedo influences the accuracy of the cloud optical thickness retrieval. In cloudy cases the transition of reflected radiance from open water to sea ice is not instantaneous but horizontally smoothed. In general, clouds reduce the reflected radiance above bright surfaces in the vicinity of open water, while it is enhanced above open sea. This results in an overestimation of to up to 90% in retrievals of the optical thickness. This effect is investigated. Using observations and three-dimensional radiative transfer simulations, this effect is quantified to range to up to 2200 m distance to the sea-ice edge (for dark-ocean albedo of αwater = 0.042 and sea-ice albedo of αice = 0.91 at 645 nm wavelength) and to depend on macrophysical cloud and sea-ice properties. The retrieved fields of cloud optical thickness are statistically investigated. Auto–correlation functions and power spectral density analysis reveal that in case of clouds with prevailing directional cloud structures, cloud inhomogeneities cannot be described by a universally valid parameter. They have to be defined along and across the prevailing cloud structures to avoid uncertainties up to 85%. / Im folgenden wird die Entwicklung und Anwendung neuer Ableitungsverfahren von Wolkenparametern, basierend auf bodengebundener und flugzeuggetragener spektraler Strahldichtemessungen über heterogenen Untergründen, vorgestellt und das Fernerkundungspotential abbildender Spektrometer evaluiert. Die spektralen Strahldichtefelder wurden während zweier internationaler Feldkampagnen im sichtbaren Wellenlängenbereich (400–970 nm) mit hoher räumlich Auflösung (<10m) gemessen. Bodengebundene Messungen wurden genutzt, um hohe Eiswolken zu beobachten und flugzeuggetragenen um arktischen Stratus zu beobachten. Aus den Messungen werden räumlich hochaufgelöste wolkenoptische Dicken abgeleitet und anschließend horizontale Wolkeninhomogenitäten untersucht. Die Ableitung der wolkenoptischen Dicke birgt je nach Messkonfiguration verschiedene Unsicherheiten. Eine Reduzierung der Unsicherheiten wird durch die Vorgabe einer Eiskristallform zur Verbesserung der Ableitung der optischen Dicke hoher Eiswolken erreicht. Diese werden unabhängig aus den winkelabhängigen, in das gemessene Strahldichtefeld eingeprägten Eigenschaften der Streuphasenfunktion, abgeleitet. Bei Vernachlässigung dieser Information und Wahl der falschen Eiskristallform, treten Fehler in der abgeleiteten optischen Dicke von bis zu 90% auf. Bei der Fernerkundung von arktischem Stratus beeinflusst die sehr variable Bodenalbedo die Genauigkeit der Ableitung der optischen Dicke. Beim Übergang von Meereis zu Wasser, findet die Abnahme der reflektierten Strahldichte im bewölktem Fall nicht direkt über der Eiskante, sondern horizontal geglättet statt. Allgemein reduzieren Wolken die reflektierte Strahldichte über Eisflächen nahe Wasser, während sie über dem Wasser erhöht wird. Dies führt zur Überschätzung der wolkenoptischen Dicke über Wasserflächen nahe Eiskanten von bis zu 90 %. Dieser Effekt wird mit Hilfe von Beobachtungen und dreidimensionalen Strahlungstransferrechnungen untersucht und es wird gezeigt, dass sein Einfluss noch bis zu 2200 m Entfernung zur Eiskante wirkt (für Meeresalbedo 0.042 und Meereisalbedo 0.91 bei 645 nm Wellenlänge) und von den makrophysikalischen Wolken- und Meereiseigenschaften abhängt. Die abgeleiteten Felder der optischen Dicke werden statistisch ausgewertet, um die Inhomogeneität der Wolken zu charakterisieren. Autokorrelationsfunktionen und Leistungsdichtespektren zeigen, dass Inhomogenitäten von Wolken mit vorranging richtungsabhängiger Struktur nicht mit einem allgemeingültigen Parameter beschrieben werden können. Es sind Inhomogenitätsmaße entlang und entgegen der jeweiligen Wolkenstrukturen nötig, um Fehler von bis zu 85% zu vermeiden.

Remote sensing is a powerful tool for studying the marine environment; however, many images are contaminated by sun glint, the specular reflection of light from the water surface. Improved radiative transfer modelling could lead to better methods for estimating and correcting sunglint. This thesis explores the effect of using detailed numerical models of the sea surface when investigating the transfer of light through the atmosphere-ocean system. New numerical realisations that model both the shape and slope of the sea surface have been created; these contrast with existing radiative transfer models, where the air-water interface has slope but not elevation. Surface realisations including features on a scale from 3 mm to 200 m were created by a Fourier synthesis method, using up to date spectra of the wind-blown sea surface. The surfaces had mean square slopes and elevation variances in line with those of observed seas, for wind speeds up to 15 m/s. Ray-tracing using the new surfaces gave estimates of reflected radiance that were similar to those made using slope statistics methods, but significantly different in 41% of cases tested. The mean difference in the reflected radiance at these points was 19%, median 7%. Elevation-based surfaces give increased sideways scattering and reduced forward scattering of light incident on the sea surface. The elevation-based models have been applied to estimate pixel-pixel variation in ocean colour imagery and to simulate scenes viewed by three types of sensor. The simulations correctly estimated the size and position of the glint zone. Simulations of two ocean colour images gave a lower peak reflectance than the original values, but higher reflectance at the edge of the glint zone. The use of the simulation to test glint correction methods has been demonstrated, as have global Monte Carlo techniques for investigating sensitivity and uncertainty in sun glint correction. This work has shown that elevation-based sea surface models can be created and tested using readily-available computer hardware. The new model can be used to simulate glint in a variety of situations, giving a tool for testing glint correction methods. It could also be used for glint correction directly, by predicting the level of sun glint in a given set of conditions.

We introduce a new suite of radiation- hydrodynamical simulations of galaxy formation and reionization called Aurora. The Aurora simulations make use of a spatially adaptive radiative transfer technique that lets us accurately capture the small- scale structure in the gas at the resolution of the hydrodynamics, in cosmological volumes. In addition to ionizing radiation, Aurora includes galactic winds driven by star formation and the enrichment of the universe with metals synthesized in the stars. Our reference simulation uses 2 x 512(3) dark matter and gas particles in a box of size 25 h(-1) comoving Mpc with a force softening scale of at most 0.28 h(-1) kpc. It is accompanied by simulations in larger and smaller boxes and at higher and lower resolution, employing up to 2 x 1024(3) particles, to investigate numerical convergence. All simulations are calibrated to yield simulated star formation rate functions in close agreement with observational constraints at redshift z = 7 and to achieve reionization at z approximate to 8.3, which is consistent with the observed optical depth to reionization. We focus on the design and calibration of the simulations and present some first results. The median stellar metallicities of low- mass galaxies at z = 6 are consistent with the metallicities of dwarf galaxies in the Local Group, which are believed to have formed most of their stars at high redshifts. After reionization, the mean photoionization rate decreases systematically with increasing resolution. This coincides with a systematic increase in the abundance of neutral hydrogen absorbers in the intergalactic medium.

We present a new analysis of multi-epoch, H-band, scattered light images of the AB Aur system. We use a Monte Carlo radiative transfer code to simultaneously model the system's spectral energy distribution (SED) and H-band polarized intensity (PI) imagery. We find that a disk-dominated model, as opposed to one that is envelope-dominated, can plausibly reproduce AB Aur's SED and near-IR imagery. This is consistent with previous modeling attempts presented in the literature and supports the idea that at least a subset of AB Aur's spirals originate within the disk. In light of this, we also analyzed the movement of spiral structures in multi-epoch H-band total light and PI imagery of the disk. We detect no significant rotation or change in spatial location of the spiral structures in these data, which span a 5.8-year baseline. If such structures are caused by disk-planet interactions, the lack of observed rotation constrains the location of the orbit of planetary perturbers to be >47 au.

Le sondeur hyperspectral infrarouge IASI, dont le premier modèle vole depuis 2006 sur le satellite défilant météorologique Metop-A, a déjà conduit a des retombées scientifiques très spectaculaires, en prévision météorologie et pour l’étude de la composition atmosphérique et du climat. Les mesures du sondeurs sont toutefois largement sous exploitées en grande partie du a la présence des nuages dans l’atmosphère. Ces derniers interagissent avec le rayonnement incident de façon hautement non-linéaire rendant le traitement de la mesure du sondeur bien plus complexe, voire parfois rédhibitoire pour accéder depuis l’espace aux propriétés des couches atmosphériques situées au-dessus du nuage, mais également en dessous dans le cas de semi-transparence. Cependant, au vue de la quantité d’informations potentielles qu’offre les sondeurs, la communauté scientifique s’intéresse de près a l’exploitation des radiances nuageuse, c’est dans ce cadre que s’inscrivent les travaux de recherche de cette thèse. Nous proposons d’étudier deux schémas nuageux radicalement différents : la clarification nuageuse et un schéma permettant de simuler la radiance nuageuse en utilisant les propriétés optique et microphysique des nuages. La première de ces méthodes, initiée par Smith et al. (1968), permet sous certaines conditions, de faire abstraction du nuage dans le pixel IASI. La méthode est basée sur l’algorithme du logiciel Scenes Heterogenes du CNES. Apres une première étape de validation, les performances de la méthode sont évaluées a travers la quantité d’information indépendante qu’offre la clarification par rapport a une chaine de traitement des radiances nuageuses mise en place au CMS. Les résultats sont favorables à la méthode testée permettant de traiter les couches atmosphériques situées sous le nuage, possédant donc une quantité plus importante. Cependant la clarification repose a la fois sur une hypothèse forte d’homogénéité atmosphérique et ne s’applique qu’à 15% des situations nuageuses. La seconde méthode est une simulation de la radiance nuageuse par des modèles de transfert radiatif rapides utilisant les propriétés optique et microphysique du nuage. Cette méthode présente l’avantage majeur d’utiliser les mêmes profils nuageux que ceux produits par les modèles de prévision numérique, laissant entrevoir l’assimilation de ces profils à partir de la mesure IASI. Cependant, l’utilisation de ces modèles de transfert radiatif rapide dans le cadre d’une assimilation de données n’en est encore qu’à ces prémices, très peu d’études ont été menées sur ce sujet. Nous proposons une étude en trois étapes permettant une utilisation en opérationnel de ces modèles de transfert radiatif. La première étape est une compréhension des modèles et de leur validité en réalisant quelques études de cas s’appuyant sur la campagne de mesures de Lindenberg. Ensuite, dans le cadre de la campagne ConcordIasi, une statistique est réalisée mettant en place des filtrage pour sélectionner uniquement les profils nuageux cohérent avec l’observation IASI. La dernière étape est une application en global, les statistiques révèlent une nette amélioration des écarts a l’ébauche grâce aux filtres, passant de 8K a 2K. Nous proposons tout au long de l’étude une discussion sur les modèles utilises (RTTOV et HISCRTM), leurs points forts et leurs défaillances. Enfin l’ultime étape, permet d’évaluer les performances des profils nuageux issus des modèles de prévision numérique. / The IASI hyperspectral infrared sounding interferometer, the first model of which has been flown on board the meteorological polar orbiting satellite MetOp-A since 2006, has already led to spectacular scientific breakthroughs in both weather forecasting and research into atmospheric composition and the climate. Measurements from the sounders are however largely underutilised, mainly because of the presence of clouds in the atmosphere. The highly non-linear way in which the clouds interact with incident radiation makes analysis of the readings much more complex, and can sometimes even prohibit access from space to the properties of not only the atmospheric layers located above the cloud, but also below them in the case of semi-transparency. However, in view of the potential amount of information offered by the sounders, the scientific community is very interested in exploiting cloud radiance. The research for this thesis stems from this interest. We plan to study two radically different cloud schemes: cloud clarification and a scheme which allows for simulation of cloud radiance by using the optical and microphysical properties of clouds. The first of these methods, initiated by Smith et al. (1968), allows us under certain conditions to disregard the cloud in the IASI pixel. This method is based on the CNES Heterogeneous Scenes software algorithm. After a first validation step, method performance is evaluated by the amount of independent information offered by the clarification, compared to a cloud radiance process chain established at CMS. The results are favorable to the tested method allowing us to deal with atmospheric layers under the cloud, which have therefore larger quantities. However clarification is based on a strong assumption of atmospheric homogeneity and only applies to 15% of cloud situations. The second method is a simulation of cloud radiance by fast radiative transfer models using the optical and microphysical properties of the cloud. The major advantage of this method is that it uses the same cloud profiles as those produced by numerical weather prediction models, allowing assimilation of these profiles from the IASI measurement. However, the use of these fast radiative transfer models in the context of data assimilation is still in the early stages, very few studies have been conducted on this topic. We are proposing a three-phase study which will allow for an operational use of these radiative transfer models. The first step is validation. This is done by conducting several case studies based on Lindenberg’s measurement campaign. Then, within the framework of the ConcordIasi campaign, a statistical analysis will be carried out by introducing filtering, to select cloud profiles which are consistent with the IASI observations. The last step is an overall application, the statistics showing a clear improvement in deviation from the draft thanks to the filters, going from 8K to 2K. Throughout the study we will discuss the models used (RTTOV and HISCRTM), their strengths and weaknesses. Finally the last step allows us to evaluate the performance of the cloud profiles obtained by the digital forecasting models