Mass loss, in the form of slow stellar winds, is a decisive factor for the evolution of cool luminous giants, eventually turning them into white dwarfs. These dense outflows are also a key factor in the enrichment of the interstellar medium with newly produced elements from the interior of these stars. There are strong indications that these winds are accelerated by radiation pressure on dust grains, but the actual grain species responsible for driving the outflows in M-type Asymptotic Giant Branch stars are still a matter of debate. Observations of dust features in the circumstellar environment of these stars suggest that magnesium-iron silicates are possible wind-drivers. However, the optical properties of these silicate grains are strongly influenced by the Fe-content. Fe-bearing condensates heat up strongly when interacting with the radiation field and therefore cannot form close enough to the star to trigger outflows. Fe-free condensates, on the other hand, have a low absorption cross-section at near-IR wavelengths where AGB stars emit most of their flux.  To solve this conundrum, it has been suggested that winds of M-type AGB stars may be driven by photon scattering on Fe-free silicate grains with sizes comparable to the wavelength of the flux maximum, rather than by true absorption. In this thesis we investigate dynamical models of M-type AGB stars, using Fe-free silicates as the wind-driving dust species. According to our findings these models produce both dynamic and photometric properties consistent with observations. Especially noteworthy are the large photometric variations in the visual band during a pulsation cycle, seen both in the observed and synthetic fluxes. A closer examination of the models reveals that these variations are caused by changes in the molecular layers, and not by changes in the dust. This is a strong indication that stellar winds of M-type AGB stars are driven by dust materials that are very transparent in the visual and near-infrared wavelength regions, otherwise these molecular effects would not be visible.

abstract: Recently, nanostructured metamaterials have attracted lots of attentions due to its tunable artificial properties. In particular, nanowire/nanohole based metamaterials which are known of the capability of large area fabrication were intensively studied. Most of the studies are only based on the electrical responses of the metamaterials; however, magnetic response, is usually neglected since magnetic material does not exist naturally within the visible or infrared range. For the past few years, artificial magnetic response from nanostructure based metamaterials has been proposed. This reveals the possibility of exciting resonance modes based on magnetic responses in nanowire/nanohole metamaterials which can potentially provide additional enhancement on radiative transport. On the other hand, beyond classical far-field radiative heat transfer, near-field radiation which is known of exceeding the Planck’s blackbody limit has also become a hot topic in the field. This PhD dissertation aims to obtain a deep fundamental understanding of nanowire/nanohole based metamaterials in both far-field and near-field in terms of both electrical and magnetic responses. The underlying mechanisms that can be excited by nanowire/nanohole metamaterials such as electrical surface plasmon polariton, magnetic hyperbolic mode, magnetic polariton, etc., will be theoretically studied in both far-field and near-field. Furthermore, other than conventional effective medium theory which only considers the electrical response of metamaterials, the artificial magnetic response of metamaterials will also be studied through parameter retrieval of far-field optical and radiative properties for studying near-field radiative transport. Moreover, a custom-made AFM tip based metrology will be employed to experimentally study near-field radiative transfer between a plate and a sphere separated by nanometer vacuum gaps in vacuum. This transformative research will break new ground in nanoscale radiative heat transfer for various applications in energy systems, thermal management, and thermal imaging and sensing. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2017

Le bilan d'énergie de surface du Plateau Antarctique est essentiellement contrôlé par les propriétés physiques des premiers centimètres du manteau neigeux. Or l'évolution de cette neige de surface est complexe car elle dépend de processus fondamentalement imbriqués: vitesse de métamorphisme, profils de température, pénétration du rayonnement solaire, précipitations, transport de neige par le vent, etc. L'objectif de ces travaux de thèse est d'étudier ces diverses composantes et leur couplage afin de simuler l'évolution de la densité de la neige et de la taille de grain (surface spécifique) sur le Plateau Antarctique. Pour représenter de manière physique l'absorption de l'énergie solaire à l'intérieur du manteau, un modèle de transfert radiatif à fine résolution spectrale (TARTES) a été implémenté dans le modèle de manteau neigeux détaillé Crocus. TARTES permet de calculer le profil vertical d'absorption d'énergie dans un manteau stratifié dont les caractéristiques sont connues. Parmi elles, la forme des grains, explicitement prise en compte dans TARTES, a été peu étudiée jusqu'à présent. C'est pourquoi une méthode de détermination expérimentale de la forme optique des grains est proposée et appliquée à un grand nombre d'échantillons de neige. Cette méthode, basée sur des mesures optiques, des simulations TARTES, et l'inférence bayésienne, a permis de déterminer la forme la plus adéquate pour simuler les propriétés optiques de la neige, et a mis en évidence le fait que représenter la neige par un ensemble de particules sphériques conduisait à surestimer la profondeur de pénétration du rayonnement d'environ 30%. L'impact de l'absorption en profondeur du rayonnement sur les profils de température dans le manteau et son métamorphisme est ensuite étudié par des approches analytique et numérique, mettant en valeur la sensibilité des profils aux propriétés de la neige proche de la surface. En particulier, la densité de la neige sur les premiers centimètres est cruciale pour le bilan d'énergie du manteau car elle impacte à la fois la profondeur de pénétration du rayonnement et la conductivité thermique du manteau. Puisque le modèle Crocus tient compte de ce couplage entre propriétés optiques et physiques du manteau, il est utilisé pour estimer l'influence des conditions météorologiques sur la variabilité temporelle des propriétés physiques de la neige de surface à Dôme C. Ces simulations sont évaluées au regard d'un jeu de données collectées lors de missions de terrain et de mesures automatiques de l'albédo spectral et de la pénétration du rayonnement dans la neige. Ces observations mettent en évidence le rôle primordial des précipitations dans les variations rapides de taille de grain en surface et l'existence d'un cycle saisonnier de cette taille de grain. Ces variations sont bien simulées par Crocus lorsque le forçage atmosphérique qui lui est imposé est adéquat. En particulier, l'impact du vent sur l'évolution du manteau est fondamental car il contrôle la densité de surface par le biais du transport de neige. Ce transport est aussi à l'origine de la variabilité spatiale des propriétés de la neige observée à Dôme C. C'est pourquoi une modélisation stochastique de l'érosion et du transport de neige dans Crocus est proposée. En plus d'expliquer la variabilité spatiale de la densité et de la taille de grain, elle permet de reproduire celle de l'accumulation annuelle ainsi que les variations rapides de hauteur de neige liées à des épisodes de vent. Ces travaux ont permis une meilleure représentation des processus physiques qui contrôlent les variations des propriétés de la neige de surface à Dôme C, tout en soulignant le rôle primordial du vent, dont l'impact sur le manteau est particulièrement complexe à simuler. / The surface energy balance of the Antarctic Plateau is mainly governed by the physical properties of the snowpack in the topmost centimeters, whose evolution is driven by intricated processes such as: snow metamorphism, temperature profiles variations, solar radiation penetration, precipitation, snow drift, etc. This thesis focuses on the interactions between all these components and aims at simulating the evolution of snow density and snow grain size (specific surface area) on the Antarctic Plateau. To physically model the absorption of solar radiation within the snowpack, a radiative transfer model with high spectral resolution (TARTES) is implemented in the detailed snowpack model Crocus. TARTES calculates the vertical profile of absorbed radiation in a layered snowpack whose characteristics are given. These characteristics include snow grain shape, a parameter that has been seldom studied. For this reason, an experimental method to estimate the optical grain shape is proposed and applied to a large number of snow samples. This method, which combines optical measurements, TARTES simulations and Bayesian inference, is used to estimate the optimal shape to be used in snow optical models. In addition, it highlights that representing snow as a collection of spherical particles results in overestimation of the penetration depth of solar radiation. The influence of the penetration of solar radiation on the snow temperature profiles is then investigated with analytical and numerical tools. The results point out the high sensitivity of the temperature profiles to surface snow physical properties. In particular, the density of the topmost centimeters of the snowpack is critical for the energy budget of the snowpack because it impacts both the effective thermal conductivity and the penetration depth of light. To simulate the evolution of snow physical properties at Dome C by taking into account their interdependence with snow optical properties, the model Crocus is used, driven by meteorological data. These simulations are evaluated against a set of data collected during field missions as well as automatic measurements of snow spectral albedo and penetration depth. These observations highlight the influence of weather conditions on the temporal variability of surface snow properties. They show the existence of a slow decrease of snow grain size at the surface during summer. Rapid changes are also observed, essentially due to precipitation. These variations are well simulated by Crocus when forced by an appropriate atmospheric forcing. In particular, the impact of wind on the evolution of the snowpack is crucial because it controls the surface density through snow transport. This transport is also responsible for the spatial variability of snow properties observed at Dome C. That is why a stochastic representation of snow erosion and transport in Crocus is proposed. It explains well the observations of the spatial variability of density and grain size, and reproduces the variability of the annual accumulation as well as rapid changes in snow height resulting from drift events. This study improves our understanding of the physical processes which drive the properties of snow close to the surface on the Antarctic Plateau, and also points out the critical role of wind, the impact of which is very difficult to account for in models yet.

La prédiction de l'émission infrarouge des jets de propulseurs composites aluminisés nécessite principalement trois étapes : le calcul des grandeurs aérothermochimiques du jet, la conversion de ces grandeurs en propriétés optiques (coefficient d'absorption, coefficient de diffusion, fonction de phase) puis la résolution de l'équation de transfert radiatif. Cette thèse,essentiellement consacrée à cette troisième étape, propose de nouvelles voies pour l'application des modèles de bande aux cas de milieux biphasiques et diffusants.D'une part, nous avons étendu ces modèles aux cas de milieux caractérisés par un déséquilibre thermique entre gaz et particules. D'autre part, nous avons proposé une méthode de séparation de la luminance en deux contributions, appelées respectivement non diffusée et diffusée, à partir d'une idée originale de Liu et al. La contribution non diffusée est solution de l'équation de transfert radiatif obtenue en ignorant les effets de la diffusion. Par conséquent, elle peut être résolue par une formulation en modèles de bande. Cette approche permet de réduire les erreurs de corrélations spectrales au seul terme de luminance diffusée.Nous avons montré l'intérêt de ces approches par comparaison avec une résolution de l'équation de transfert radiatif en raie par raie, sur des milieux représentatifs de situations de télédétection de jets. / Prediction of infrared emission of exhaust plumes from aluminized composite rocket, follows mainly three steps : calculating aero-thermo-chemical values in the plume, converting those valuesto optical properties (absorption coefficient, scattering coefficient and phase function) and resolving the radiative transfer equation. This thesis is mostly devoted to this third step, and proposes new ways to use band models on two-phases and scattering media.Firstly, we extended band models to cases with thermic non equilibrium between gas and particles. Secondly, we proposed a method consisting in splitting radiance in two parts, one called un-scattered and the other scattered, from an original idea of Liu et al. The un-scattered part is solution of the radiative transfer equation obtained by ignoring scattering. As a result, the unscattered radiance can be found by using band models. By this approach, errors on spectral correlations are only present on the scattered radiance.We show the interest of thoses approches by comparing them with a line by line resolutionof the radiative transfer equation, on media representative of remote sensing cases of rocket exhaust plumes.

Le processus de formation d’étoiles se déroule selon plusieurs phases. Tout d’abord une phase à grande échelle, durant laquelle le nuage moléculaire se fragmente sous l’action de sa propre gravité et de la turbulence en coeurs denses gravitationnellement instables. Dans ces fragments le milieu est optiquement mince, l’énergie libérée par le travail de compression s’échappe sous forme de rayonnement, d’où un processus quasi isotherme. Lorsque le nuage devient optiquement épais à son propre rayonnement, la matière en effondrement forme un objet en équilibre hydrostatique appelé premier cœur dit de Larson. S’ensuit une phase d’accrétion, qui conduit ultimement à la dissociation du dihydrogène. Une partie du travail de compression est alors absorbée par l'énergie de dissociation de la molécule, et non plus convertie en énergie thermique, permettant à l'effondrement de recommencer. Lorsque que toutes les molécules de dihydrogene ont été dissociées, la phase adiabatique recommence et le second cœur de Larson (proto-étoile) est formé.L'ajout des éléments nécessaires au traitement de la magnétohydrodynamique (MHD) non-idéale dans le code à grille adaptative RAMSES constitue la première partie de la thèse. L'étude détaillée des stades ultimes (premier et second cœur de Larson) de la formation des étoiles constitue la seconde partie de la thèse. Cette étude a pu mettre en évidence des effets importants de la MHD non-idéale sur la répartition du champ magnétique et l'efficacité du transport de moment angulaire. / Stars formation occurs in several steps. First a large scale phase during which the molecular cloud undergo fragmentation due to its self-gravity and turbulence. In the gravitationally unstable fragments the medium is optically thin causing all the energy generated by the collapse to escape freely. This is called the isothermal compression phase. When the cloud becomes optically thick to its own radiation, an hydrostatic core forms: the first Larson core. Follow an adiabatic accretion phase ending up ultimately in the dissociation of dihydrogen molecules. Part of the energy from the gravitational collapse is absorbed by the chemical process allowing for another quasi isothermal collapse to start until depletion of dihydrogen molecules. When the adiabatic phase is restored, the second Larson core (proto-star) is formed.Coding the non-ideal magnetohydrodynamics (MHD) solver in the adaptive mesh refinement code RAMSES has been the focus for the first part of the thesis. The precise study of the last steps (first and second Larson core) of star formation is the second part of the thesis. This study highlighted the impact of non-ideal MHD on the magnetic field repartition and the efficiency of the angular momentum transport.

L'atténuation est un paramètre clé dans l'évaluation de l'aléa sismique car elle contrôle l'amplitude et la durée du mouvement du sol. Deux mécanismes contribuent à l'atténuation des ondes sismiques courte-période (f>1Hz, avec f la fréquence) : (1) l'absorption, quantifiée par son facteur de qualité Qi(f); et (2) le scattering, quantifié par Qsc(f). L'objectif principal de cette thèse est de cartographier l'atténuation sismique en France Métropolitaine en déterminant l'importance relative de ces deux processus. Pour mener à bien cette tâche, nous avons modélisé le transport de l'énergie sismique multi-diffusée - aussi appelée coda sismique - à l'aide de l'équation de transfert radiatif dans un milieu présentant des variations latérales des propriétés de diffusion et d'absorption. En utilisant une approche perturbative, nous avons calculé les noyaux de sensibilité de l'intensité de la coda sismique à des variations spatiales de Qi(f) et Qsc(f) à 2-D, dans le cas où la diffusion est isotrope. Dans un deuxième temps, nous avons mesuré la vitesse de décroissance énergétique de la coda sismique, quantifiée par le facteur de qualité de la coda Qc(f), sur plus de 120000 formes d'onde collectées en France, en Belgique et sur l'ensemble de l'arc alpin. L'approche théorique développée dans cette thèse nous a permis d'établir une relation approximative entre Qc et Qi. Cette relation prend la forme d'une intégrale de Qi sur le rai direct reliant la source à la station. Cette approximation a été utilisée afin de cartographier pour la première fois les variations régionales de l'absorption entre 1 et 32 Hz dans les Alpes et en France Métropolitaine. Nos résultats mettent en évidence de très fortes variations latérales (±30%) de l'absorption. À basse fréquence (f~1Hz), une corrélation claire apparaît entre la géologie de surface et les structures d'absorption : les zones de forte absorption se localisent sur les séries sédimentaires peu consolidées tandis que les régions de faible absorption correspondent au socle affleurant dans le Massif Armoricain, le Massif Central et dans les chaînes de montagne comme les Pyrénées et les Alpes. À haute fréquence (f~24Hz), la corrélation entre géologie de surface et atténuation disparaît. Nous avons formulé l'hypothèse que la dépendance fréquentielle de la structure en atténuation est due à un changement du contenu ondulatoire de la coda sismique avec la fréquence. Ainsi la sensibilité de la coda aux structures profondes de la croûte augmenterait avec la fréquence. Enfin, nous avons initié la mise en oeuvre des noyaux de sensibilité isotrope exacts à 2-D afin d'obtenir une tomographie d'absorption. L'inversion des mesures de Qc par décomposition en valeurs singulières nous a permis de construire la première tomographie d'absorption qui tienne compte de toute la sensibilité des trajets des ondes multi-diffusées. La carte préliminaire d'absorption obtenue pour les Pyrénées est prometteuse. Nos résultats fournissent des bases théoriques solides pour l'inversion linéarisée de Qsc et Qi à partir de la coda sismique. Ils offrent également des informations complémentaires aux tomographies de vitesse et des perspectives d'amélioration de la régionalisation des calculs de l'aléa sismique en France Métropolitaine. / Attenuation is a key parameter for seismic hazard assessment. It plays an important role in the observed variability of ground motion amplitude and duration. There are two main causes for attenuation of short period seismic waves (f>1Hz, with f the frequency) : (1) absorption, quantified by the quality factor Qi ; and (2) scattering, quantified by Qsc. The main objective of this thesis is to map the seismic attenuation in Metropolitan France and to determine the relative importance of these two processes. To model the transport of multiply-scattered seismic waves - also known as the seismic coda - we employ a scalar version of the radiative transfer equation with spatially dependent absorption and scattering properties. The sensitivity kernels of the coda intensity to spatial variations of Qi and Qsc are computed in 2-D isotropically and anisotropically scattering media. The coda quality factor Qc (f) - quantifying the decay rate of the seismic coda energy - have been estimated on a collection of 120000 waveforms recorded in France, Belgium and in the Alpine range. According to the theory developed in this thesis, we establish a linearized approximate relation between the coda quality factor Qc (f) and the absorption quality factor Qi. This relation is expressed as an integral along the direct ray path connecting the source to the station. This approximation is used to map regional variations of absorption in the Alps and in Metropolitan France between 1 and 32Hz. Our maps reveal strong lateral variations (±30%) of absorption in the crust. At low frequency (f~1Hz), the correlation between sedimentary deposits and high absorption regions is clear : strong absorption zones are localized on the poorly consolidated sedimentary series while low absorption regions correspond to the basement which outcrops in the Massif Armoricain, the Massif Central and in the mountain ranges as the Pyrenees or the Alps. At high frequency (f~24Hz), the correlation between surface geology and absorption structures tends to disappear. We hypothesize that the frequency dependence of the attenuation structure is caused by a change of the wavefield composition which accentuates the sensitivity of the coda to the deeper parts of the medium as the frequency increases. Finally, we initiate the implementation of the exact 2D isotropic sensitivity kernels to retrieve the crustal absorption structures. Using the linear relation between Qc and Qi, we obtain the first absorption map which takes into account the precise spatio-temporal sensitivity of coda waves. The inverse problem is solved with a singular value decomposition approach. The preliminary map of Qi for the Pyrenees is promising. Our results constitute a solid theoretical basis to develop linearized inversions of Qsc and Qi from the analysis of the seismic coda. They also significantly improve the knowledge of the regional variations of seismic attenuation in Metropolitan France. Our maps provide new insights on the crustal structure of the Alpine Range in complement to seismic velocity images. These attenuation maps have direct implication for the design of future seismic hazard maps.

Tropical forests, which provide important ecosystem functions and services, are increasingly threatened by anthropogenic pressures. This has resulted in an urgent need to understand tree species diversity of those forests. Where knowledge of that diversity is largely from the botanical surveys and local ecological studies, data must inevitably be up-scaled from point observations to the landscape and regional level if a holistic perspective is required. This thesis explores aspects of the spatio-temporal heterogeneity of canopy reflectance patterns over the forests of French Guiana, in order to assess whether this information could help defining an ecologically consistent forest typology. To gain insight into both the spatial and temporal heterogeneity of French Guiana’s forests, instrumental artefacts affecting the satellite data first had to be addressed. Data used in this study represent the spectral response of forest canopies, and the way in which such data are captured makes them susceptible to the ‘bi-directional reflectance distribution function’ (BRDF). BRDF indicates that objects do not reflect light in equal proportions in all directions (isotropically). Thus, forest canopies will reflect light anisotropically depending on factors including canopy roughness, leaf optical properties and inclination, and the position of the sun relative to the sensor. The second chapter of this thesis examines how BRDF affects the canopy reflectance of forests in French Guiana, and how not correcting for BRDF affects spectral classifications of those forests. When monthly reflectance data corrected for the artefact are examined, these suggest seasonally-occurring changes in forest structure or spectral properties of French Guiana’s forests. The third chapter of this thesis thus examines temporal effects of BRDF, and used cross-regional comparisons and plot-level radiative transfer modelling to seek to understand the drivers of the monthly variation of the forests’ canopy reflectance. For the latter, the Discrete Anisotropic Radiative Transfer (DART) model was used along with aerial laser scanning (ALS) observations over different forest structures, indicating that the observed variation in reflectance (and derivatives known as vegetation indices) could not be explained by monthly variations in solar direction. At the regional scale, it was also demonstrated that forests in the Guiana Shield possess temporal variation distinct from forests in central Africa or northern Borneo, forests also lying just above the Equator. Had the observed temporal variation in vegetation indices been the result of BRDF, it would have been expected that the forests in the three zones would have similar patterns of variation, which they did not. Central African forests appear to have their greening synchronized with rainfall, whereas forests in the Guianas appear synchronized with the availability of solar radiation. Further analysis of the vegetation index time-series of observations also indicated that different types of forests in French Guiana possess distinct patterns of temporal variation, suggesting that tropical forest types can be discriminated on the basis of their respective “temporal signatures.” That was exploited in the fourth chapter of the thesis, which maps forests in French Guiana based on their combined spatio-temporal canopy reflectance patterns and by so doing presents a novel way of addressing forest typology, based on ecologically meaningful information. The thesis presented demonstrates that it is possible to adequately address remote sensing data artefacts to examine patterns of spatial and temporal variation in tropical forests. It has shown that phenological patterns of tropical rainforests can be deduced from remote sensing data, and that forest types can be mapped based on spatio-temporal canopy reflectance patterns. It is thus an important contribution to understand the ecology of tropical forests in French Guiana and to improve the toolbox of scientists dealing with the identification of spatio-temporal patterns observable in forests at the landscape level.

Hlavním cílem práce bylo zlepšení kvantitativních odhadů vegetačních parametrů smrkových porostů pomocí spektrálních simulací trojrozměrného modelu přenosu záření. Prvně bylo potřeba vytvořit přesný 3D model smrku. Implementace přesného 3D modelu smrku pro parametrizaci celých lesních porostů je v současné době výpočetně nemožné, bylo tedy nutné tento 3D model smrku zjednodušit. Přesný 3D model smrku společně s dostupnými leteckými daty sloužil pro nalezení optimálního zjednodušení. Optimální model vedl ke kompromisu mezi výpočetní náročností a přesností výsledné odrazivosti z modelu přenosu záření. Následně byl optimální model smrku využit pro odhady vegetačních parametrů ze satelitních snímků. Přesnost odhadů byla ověřena oproti pozemním měřením odhadovaných parametrů. Na závěr byly porovnány výsledky z odhadů vegetačních parametrů pomocí optimálního 3D modelu smrku s výsledky z tradičního přístupu pomocí modelů stromu s geometricky jednodušími tvary korun.

In this thesis spectral solar zenith radiances are analyzed which were obtained from ship-based measurements over the Atlantic ocean. In combination with high-resolution lidar and microwave remote sensing optical and microphysical cloud properties were retrieved using spectral radiation data. To overcome problems of existing transmissivity-based cloud retrievals, a new retrieval algorithm is introduced which circumvents retrieval ambiguities and reduces the influence of measurement uncertainties. The method matches radiation measurements of ratios of spectral transmissivity at six wavelengths with modeled transmissivities. The new retrieval method is fast and accurate, and thus suitable for operational purposes. It is applied to homogeneous and inhomogeneous liquid water and cirrus clouds. The results from the new algorithm are compared to observations of liquid water path obtained from a microwave radiometer, yielding an overestimation for thick liquid water clouds but a slight underestimation for thin clouds. A statistical analysis of retrieved cloud properties during three Atlantic transects is introduced. Similar characteristics of cloud properties are found in the mid latitudes and northern subtropics but the large variability of meridional distribution in the remaining regions imply the prevailing influence of weather systems compared to typical cloud distributions. With about 63% homogeneous stratocumulus clouds are found to be the prevailing cloud type over ocean, while scattered and inhomogeneous liquid water clouds amount to 16% and 21%, respectively. All analyzed distributions are affected by an increased frequency of small values of cloud properties caused by 3D radiative effects. The comparison with satellite-based and ship-based cloud retrievals along the cruise track show comparable results for the cloud optical thickness with limitations for thick liquid water clouds. The meridional distribution of effective radius agreed within the uncertainties of both methods, however, the satellite-derived values are biased toward larger mean values.

In this thesis a new three–dimensional (3D) vector radiative transfer model, the Solver for Polarized Atmospheric Radiative Transfer Applications (SPARTA) is introduced, validated against benchmark results, and applied to scientific problems. SPARTA employs the statistical forward Monte Carlo technique for efficient column–response pixel–based radiance calculations comprising polarization for 3D inhomogeneous cloudless and cloudy atmospheres. By means of SPARTA, two scientific issues in the field of radiative transfer are investigated. A sensitivity study has been conducted to illustrate the errors introduced by neglecting the effects of polarization in radiation simulations. Two atmospheric scenarios have been considered: a pure one–dimensional (1D) Rayleigh atmosphere and two–dimensional (2D) realistic inhomogeneous dust fields. In case of a purely molecular atmosphere, these errors strongly depend on molecular anisotropy, isotropic reflection, and more importantly, on single scattering albedo and optical thickness (saturation occurs for τ close to 1). Overall errors in the reflected field range up to about 10.5%. On the other hand, for rather high optical thickness, the bias induced by ignoring polarization for realistic inhomogeneous atmospheres is negligible (less than 1%). In addition, solar radiative transfer simulations for LIDAR–measured fields of optical properties of Saharan dust have been performed in order to quantify the effects induced by neglecting the horizontal photon transport and internal inhomogeneities (3D radiative effects) in radiance simulations including polarization. Results are presented for two exemplary mineral dust fields constructed from LIDAR observations. For each case, three radiative calculations are investigated: a 1D calculation according to the plane–parallel (1D mode); an Independent Pixel Approximation (IPA mode); and the 2D mode. The differences in domain–averaged normalized radiances of reflection and transmission are insignificant between the 1D or IPA and 2D calculation modes. However, local differences were observed since extinction is hinge on horizontal spatial variability. In the areas with large spatial variability in optical thickness, the radiance fields of the 2D mode differ about ±20% for the first and second Stokes elements (I, Q) from the fields of the 1D mode. This work points to a brand–new field: the quantification of the sensitivity of polarization to 3D radiative effects.