The Meyers et al. (2007) Tampa Bay Model produces water level and three-dimensional current and salinity fields for Tampa Bay. It is capable of computing temperature but is presently run without active thermodynamics. Variations in water temperature are driven by heat exchange at the water-atmosphere boundary and advective heat flux at the mouth of the bay. The net heat exchange surface boundary condition is required for computations of three-dimensional temperature fields. Components of the surface heat budget were measured or derived at an observational tower in Middle Tampa Bay. Net heat exchange at the surface of Tampa Bay was computed from June 2002 to May 2005. Total heat energy gained or lost at the bay-atmosphere interface includes turbulent and radiative heat fluxes. An initial examination of turbulent heat exchange, the portion of total surface heat flux driven by atmospheric turbulence, demonstrated the skill of a bulk flux algorithm (TOGA COARE v. 3.0) in predicting measured sensible heat flux over Tampa Bay (R² = 0.80 and RMSE of 11.02 W/m² from June through November of 2002). Insolation was measured directly at the observational tower. Solar radiation is reflected in proportion to sea surface albedo, computed following Payne (1972). Based upon Secchi depth readings, Tampa Bay was classified as a water body type 7. The amount of penetrating insolation reflected from the bottom was computed for this type 7 estuary. Upwelling longwave radiation is emitted in proportion to the water temperature according to the Stefan-Boltzmann law. Eleven bulk formulas for computing downwelling longwave radiation were assessed for skill in reproducing observations made at buoys moored on the West Florida Shelf. Berliand and Berliand (1952) best represented downwelling longwave heat flux measurements at the buoys and is appropriate for application over Tampa Bay. Surface heat flux dominates cooling in fall and warming in spring while advective heat exchange becomes important during the summer. Extreme events, including tropical cyclones and extratropical fronts, dramatically impact surface heat exchange, driving rapid cooling. The methods applied in computation of heat flux components are amenable to real-time modeling exercises.

The effective radiative conductivity of fibrous material is an important part of the evaluation of the thermal performance of fibrous insulators. To better evaluate this material property, a three-dimensional direct simulation model which calculates the effective radiative conductivity of fibrous material is proposed. Two different geometries are used in this analysis. The simplified model assumes that the fibers are in a cylindrical shape and does not require identically-sized fibers or a symmetric configuration. Using a geometry with properties resembling those of a fibrous insulator, a numerical calculation of the geometric configuration factor is carried out. The results show the dependency of thermal conductivity on temperature as well as the orientation of the fibers. The calculated conductivity values are also used in the continuum heat equation, and the results are compared to the ones obtained using the direct simulation approach, showing a good agreement. In continue, the simulated model is replaced by a realistic geometry obtained from X-ray micro-tomography. To study the radiative heat transfer mechanism of fibrous carbon, three-dimensional direct simulation modeling is performed. A polygonal mesh computed from tomography is used to study the effect of pore geometry on the overall radiative heat transfer performance of fibrous insulators. An robust procedure is presented for numerical calculation of the geometric configuration factor to study energy-exchange processes among small surface areas of the polygonal mesh. The methodology presented here can be applied to obtain accurate values of the effective conductivity, thereby increasing the fidelity in heat transfer analysis.

La génération actuelle des sondeurs infrarouges avancés constitue l’une des sources les plus importantes d’observation dans les systèmes d’assimilation de données dans les modèles de la Prévision Numérique du Temps (PNT). Cependant la richesse d’informations fournies par ce type de capteur avec son grand nombre de canaux et sa couverture globale est loin d’être complètement exploitée. La présence de nuages dans le champ de vision de l’instrument, qui affecte la majorité des observations, est l’une des raisons pour lesquelles les centres de PNT rejettent une grande quantité des observations des sondeurs. Les centres de PNT ont cependant commencé à assimiler au-dessus des océans les radiances affectées par les nuages en utilisant des canaux dont les effets radiatifs nuageux sont modélisés par un modèle de nuage simple. Certains de ces algorithmes de détection sont évalués dans ce manuscrit, et leurs limitations sont explicitées. Afin d’accroître la quantité de données assimilées, il est nécessaire de mieux représenter les nuages et leurs effets radiatifs. Depuis quelques années, des études ont été menées pour mieux représenter leurs effets dans les modèles de transfert radiatif ([Faijan et al., 2012] ; [Martinet et al., 2013]) ; et utiliser dans l’assimilation de nouveaux canaux infrarouges informatifs sur les hydrométéores nuageux. ([Martinet et al., 2014]). Cette thèse se concentre principalement sur ces méthodes de détection de scènes homogènes en consacrant sa majeur partie à l’établissement, l’évaluation et l’amélioration d’algorithme de détection de scènes homogènes en se basant sur la colocalistion d’observation avec d’autres sondeurs. Ces études sont rendus possibles par la prise en compte des champs d’hydrométéores fournis par les schémas convectifs du modèle ARPEGE en entrée du modèle de transfert radiatif nuageux RTTOV-CLD. Une partie validation des simulations est opérée dans cette thèse, en comparant l’apport les forces et faiblesses du schéma convectif en opérationnel ainsi que PCMT. Par la suite, différents tests, ou critères, de détection sont proposés, et en réalisant des expériences d’assimilation et en évaluant l’impact de ces ces critères de sélection proposés sur la qualité des prévisions à longues échéances, un des tests parmi ceux proposés se démarque des autres en conservant une quantité importante d’observation ciel clair et démontre des impacts neutres à légèrement positifs sur les prévisions. Les nouvelles méthodes de sélection de scènes homogènes proposées dans cette études permettent d’envisager une amélioration significative du contrôle de qualité des observation IASI en ciel clair. Cela ouvre ainsi donc la voie à une utilisation, plus maîtrisée, des scènes nuageuses. Nous expliquons dans ce manuscrit pourquoi il serait imprudent de précéder à des assimilation de radiances infrarouge contaminées par la présence de nuages. Pour contourner cette difficulté, une technique d’assimilation en deux étapes déjà utilisé pour l’assimilation des réflectivité radar ([Wattrelot et al., 2014]) dans AROME est évaluée. Cette méthode basée sur l’inversion bayésienne a récemment été adaptée pour les observations microondes satellitaire ([Duruisseau et al., 2018]). Dans cette étude, nous explorons cette technique pour les observations IASI. Plusieurs tests de sensibilité sont effectués sur les différents paramètres de l’algorithme, avec pour objectif de préparer de futurs travaux sur l’assimilation all-sky infrarouges, explicités dans les perspectives de ce manuscrit. / The current generation of advanced infrared sounders is one of the most important sources of observations in data assimilation systems in numerical weather prediction (NWP) models. However, the total amount of information provided by this type of sensor, with its large number of channels and its global coverage, is far from being fully exploited. The presence of clouds in the instrument’s field of view, which affects the majority of observations, is one of the reasons why NWP centers reject a large amount of observations from sounders. NWP centers, however, have begun to assimilate cloud-affected radiances over the oceans using channels whose cloudy radiative effects are modeled by a simple cloud model. Some of these detection algorithms are evaluated in this manuscript, and their limitations are clarified. In order to increase the amount of assimilated data, it is necessary to better represent clouds and their radiative effects in the models. For several years, studies have been conducted to better represent their effects in radiative transfer models ([Faijan et al., 2012] ; [Martinet et al., 2013]) ; and to use new informative infrared channels of cloudy hydrometeors in the assimilation. [Martinet et al., 2014]. This thesis focuses on several approaches for the assimilation of cloudy radiances. In the first part, the characterization of the cloud parameters currently used for the assimilation of cloudy radiances was evaluated in the global and regional scale models. In addition, as part of the "all-sky" assimilation, which considers both clear and cloudy radiances, the evaluation and improvement of homogeneous scene detection algorithms based on the colocation of observations with other imagers was studied. These studies are made possible by taking into account the hydrometeorological fields provided by the convective schemes of the ARPEGE model as the input of the RTTOV-CLD cloud radiative transfer model. Part of this thesis concerns the validation of simulations, by comparing the contribution of the new convective PCMT scheme to the one used in operational applications. Subsequently, different criteria for selecting homogeneous scenes are proposed. By conducting assimilation experiments and evaluating the impact of these proposed selection criteria on the quality of long-term forecasts, one of the proposed tests stands out from the others by keeping a significant amount of clear sky observations and demonstrating neutral to slightly positive impacts on the forecasts. These new methods for selecting homogeneous scenes proposed in this study allows the consideration of improving the quality control of IASI observations in clear sky. To address the issue of all-sky radiance data assimilation, the two-step assimilation technique, already used for radar reflectivity assimilation in AROME ([Wattrelot et al., 2014]), was evaluated for IASI radiances in the ARPEGE model in a case study. This method based on Bayesian inversion has recently been adapted for satellite microwave observations ([Duruisseau et al., 2018]). Several sensitivity tests were carried out on the different parameters of the algorithm, with the objective of preparing for future work on infrared all-sky assimilation, as explained in the perspectives of this manuscript.

Terahertz (THz) spectroscopy can potentially be used to probe and characterize inhomogeneous materials, however spectroscopic identification of such materials from spectral features of diffuse returns is a relatively underdeveloped area of study. In this thesis, diffuse THz scattering from granular media is modeled by applying radiative transfer (RT) theory for the first time in THz sensing. Both classical RT theory and dense media radiative transfer (DMRT) theory based on the quasi-crystalline approximation (QCA) are used to calculate diffuse scattered intensity. The numerical solutions of the vector radiative transfer equations (VRTE) were coded and calculated in MATLAB. The diffuse scattered field from compressed Polyethylene (PE) pellets containing steel spheres was measured in both transmission and reflection using a THz time domain spectroscopy (THz-TDS) system. Measurement results showed energy redistribution by granular media due to volume scattering as well as angle dependent spectral features due to Mie scattering. The RT model was validated by successfully reproducing qualitative features observed in experimental results. Diffuse intensity from granular media containing Teflon, lactose sugar, and C4 explosive was then calculated using the RT models. Simulation results showed the amplitude of diffuse intensity is affected by factors such as grain size, fractional volume of grains, thickness of scattering layer, and scattering angles. Spectral features were also observed in the diffuse intensity spectra from media containing grains with THz spectral signatures. The simulation results suggest the possibility of identifying materials from diffuse intensity spectra.

Low grade heat sources have a large amount of thermal energy content. Due to low temperature, the conventional power generation technologies result in lower efficiency and hence cannot be used. In order to efficiently generate power, alternate methods need to be used. In this study, a supercritical organic Rankine cycle was used for heat source temperatures varying from 125°C to 200°C. Organic refrigerants with zero ozone depletion potential and their mixtures were selected as working fluid for this study while the cooling water temperature was changed from 10-25°C. Operating pressure of the cycle has been optimized for each fluid at every heat source temperature to obtain the highest thermal efficiency. Energy and exergy efficiencies of the thermodynamic cycle have been obtained as a function of heat source temperature. Efficiency of a thermodynamic cycle depends significantly on the sink temperature. At areas where water cooling is not available and ambient air temperature is high, efficient power generation from low grade heat sources may be a challenge. Use of passive cooling systems coupled with the condenser was studied, so that lower sink temperatures could be obtained. Underground tunnels, buried at a depth of few meters, were used as earth-air-heat-exchanger (EAHE) through which hot ambient air was passed. It was observed that the air temperature could be lowered by 5-10°C in the EAHE. Vertical pipes were used to lower the temperature of water by 5°C by passing it underground. Nocturnal cooling of stored water has been studied that can be used to cool the working fluid in the thermodynamic cycle. It was observed that the water temperature can be lowered by 10-20°C during the night when it is allowed to cool. The amount of water lost was calculated and was found to be approximately 0.1% over 10 days. The different passive cooling systems were studied separately and their effects on the efficiency of the thermodynamic cycle were investigated. They were then combined into a novel condenser design that uses passive cooling technology to cool the working fluid that was selected in the first part of the study. It was observed that the efficiency of the cycle improved by 2-2.5% when passive cooling system was used.

Les supergéantes rouges (RSG) sont des étoiles massives ( 10 < Msun < 30) qui, grâce à leur haute luminosité infrarouge, sont des indicateurs des distances intergalactiques et des sondes de la structure galactique. La compréhension de leurs propriétés est cruciale et elle touche à différents thèmes astrophysiques.<br />Les simulations numériques 3D d'hydrodynamique radiative (RHD), obtenues avec le code CO5BOLD (Freytag, Steffen, Ludwig et al.), aident à trouver la réponse aux principales questions concernant les RSGs.<br />J'ai conçu un code de transfert radiatif en 3D qui calcule des spectres et des cartes d'intensité à partir des simulations RHD. Grâce à cet outil, j'étudie en détail les principales caractéristiques des modèles RHD à différentes longueurs d'onde. J'examine ensuite l'impact de la convection sur les raies spectrales en terme d'asymétries et de décalages, et je prédis les variations de bisecteurs et du photocentre en vue de futures observations.<br />Par la suite, je cherche les vitesses caractéristiques de l'atmosphère des RSGs, et je constate que les simulations sont en accord avec les observations même si l'amplitude des vitesses est plus petite que celle observée.<br />Les structures convectives affectent les courbes de visibilités et les clôtures de phases, qui montrent clairement une nette déviation de la symétrie circulaire. Tout en les analysant, je cherche des contraintes pour les simulations RHD et je montre que l'interférométrie est le moyen observationnel privilégié pour caractériser la convection dans les RSGs.<br />Le problème majeur des simulations RHD est le traitement gris des opacités. J'explore les effets du passage au non-gris sur les observables en utilisant un premier modèle de test non-gris.

The Indian Ocean Experiment (INDOEX) had as a primary objective determining the radiative forcing due to anthropogenic aerosols over climatologically significant space and time scales: the Indian Ocean during the winter monsoon, January-March. During the winter monsoon, polluted, low-level air from the Asian subcontinent blows over the Arabian Sea and Indian Ocean. As part of INDOEX, aerosol optical depths were derived from Advanced Very High Resolution Radiometer (AVHRR) data for the cloud-free ocean regions. The AVHRR radiances were first calibrated using the interior zone of the Antarctic and Greenland ice sheets, which proved to be radiometrically stable calibration targets. Optical depths were derived by matching the observed radiances to radiances calculated for a wide range of optical depths and viewing geometry. Optical depths derived with the AVHRR were compared with those derived with NASA's Aerosol Robotic Network (AERONET) CIMEL instrument at the Center for Clouds, Chemistry, and Climate's Kaashidhoo Observatory, as well as with other surface and shipboard observations taken in the INDOEX region. The retrieved and surface-based optical depths agreed best for a new 2-channel, 2- aerosol model scheme in which the AVHRR observations at O·64 and O·84 microns were used to determine relative amounts of marine and polluted continental aerosol and then the resulting aerosol mixture was used to derive the optical depths. Broadband radiative transfer calculations for the mixture of marine and polluted continental aerosols were combined with the 0·64 and 0·84-micron AVHRR radiances to determine the radiative forcing due to aerosols in the INDOEX region. Monthly composites of aerosol optical depth and top of the atmosphere, surface, and atmospheric radiative forcing were derived from calibrated AVHRR radiances for January-March 1996-2000. An inter-annual variability in the magnitude and spatial extent of high value regions is noted for derived optical depths and radiative forcing, with highest values reached in 1999, particularly in the Bay of Bengal which during the IFP was covered by plumes from Indochina. Frequency distributions of the optical depth for 1⁰ x 1⁰ latitude-longitude regions are well represented by gamma distribution functions. The day-to-day and year-to-year variability of the optical depth for such regions is correlated with the long term average optical depth. Interannual variability of the monthly mean optical depths for such regions is found to be as large as the day to day. / Graduation date: 2001

The atmospheric radiative transfer model MOCARAT was developed and is presented in this thesis. MOCARAT employs a Monte Carlo Technique for the accurate modeling of band radiances and reflectances in an atmospheric system with a ruffled ocean surface as a lower boundary. The atmospheric radiative transfer is modeled with consideration of molecular Rayleigh scattering, Mie Scattering and absorption on particulate matter, as well as band absorption by molecules in the wavelength channels of interest. The bidirectional reflection of downwelling light at the ocean surface is computed using the empirical relationship between surface wind field and the slope distribution of wave facets derived by Cox and Munk (1954a). A method is proposed to use the oceanic sun glint for remote sensing applications. The sensitivity of channel correlations to aerosol burden and type as well as other atmospheric and observational parameters is assessed. Comparisons of observed correlations with model results are used to check the consistency of the calibration of the airborne Multichannel Cloud Radiometer (MCR) that was employed during the Indian Ocean Experiment (INDOEX). The MCR calibration exhibited large variability from flight to flight. The method was applied to MODIS observations. Unlike the MCR, MODIS was stable where expected, although numerical values for some of the wavelengths appear to depart from theory. / Graduation date: 2004

Satellite technology represents the only technique for measuring sea surface temperatures (SSTs) on a global scale. SSTs are important as boundary conditions for climate and atmospheric boundary layer models which attempt to describe phenomena of all scales, ranging from local forecasts to predictions of global warming. Historical use of infrared satellite measurements for SST determination has been based on a theory which assumes that the atmosphere is 'thin', i.e., that atmospheric absorption of infrared radiation emitted from the sea surface has very little effect on the radiant intensity that is measured by satellites. However, a variety of independent radiative transfer models point to the possibility that the so-called 'thin approximation' is violated for humid atmospheres such as those found in the tropics, leading to errors in the retrieved SST that would be unacceptable to those who make use of such products. Furthermore, such tropical regions represent a significant portion of the globe, where coupled ocean-atmosphere disturbances can have global effects (e.g., the tropical Pacific El Nino-Southern Oscillation events). This study evaluates the thin approximation empirically, by combining radiative transfer theory and satellite data from the Eastern Atlantic ocean region studied during the Atlantic Statocumulus Transition Experiment (ASTEX). Six months of satellite data from May, June, and July of 1983 and 1984 are analyzed. To the degree that the data may be considered representative of globally valid relationships between measured variables, it is shown that the thin approximation is not appropriate for the tropics. This suggests that new methods are necessary for retrieving SSTs from the more humid regions of the globe. / Graduation date: 1993

For over 30 years, the Implicit Monte Carlo (IMC) method has been used to solve challenging problems in thermal radiative transfer. These problems are typically optically thick and di ffusive, as a consequence of the high degree of "pseudo-scattering" introduced to model the absorption and reemission of photons from a tightly-coupled, radiating material. IMC has several well-known features which could be improved: a) it can be prohibitively computationally expensive, b) it introduces statistical noise into the material and radiation temperatures, which may be problematic in multiphysics simulations, and c) under certain conditions, solutions can be unphysical and numerically unstable, in that they violate a maximum principle - IMC calculated temperatures can be greater than the maximum temperature used to drive the problem. We have developed a variant of IMC called "iterative thermal emission" IMC, which is designed to be more stable than IMC and have a reduced parameter space in which the maximum principle is violated. ITE IMC is a more implicit method version of the IMC in that it uses the information obtained from a series of IMC photon histories to improve the estimate for the end of time-step material temperature during a time step. A better estimate of the end of time-step material temperature allows for a more implicit estimate of other temperature dependent quantities: opacity, heat capacity, Fleck Factor (probability that a photon absorbed during a time step is not reemitted) and the Planckian emission source. The ITE IMC method is developed by using Taylor series expansions in material temperature in a similar manner as the IMC method. It can be implemented in a Monte Carlo computer code by running photon histories for several sub-steps in a given time-step and combining the resulting data in a thoughtful way. The ITE IMC method is then validated against 0-D and 1-D analytic solutions and compared with traditional IMC. We perform an in finite medium stability analysis of ITE IMC and show that it is slightly more numerically stable than traditional IMC. We find that significantly larger time-steps can be used with ITE IMC without violating the maximum principle, especially in problems with non-linear material properties. We also compare ITE IMC to IMC on a two-dimensional, orthogonal mesh, x-y geometry problem called the "crooked pipe" and show that our new method reproduces the IMC solution. The ITE IMC method yields results with larger variances; however, the accuracy of the solution is improved in comparison with IMC, for a given choice of spatial and temporal grid. / Graduation date: 2013