Dissertations / Theses on the topic 'Radiative transfer models (RTM)'
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1
Schlawin, Everett A. "Radiative Transfer Models of the Galactic Center." Oberlin College Honors Theses / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1249300204.
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Zhang, Hongbin 1965. "A model radiative transfer problem." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277071.
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The analytical solution to a model time-dependent continuous lethargy photon transport equation is evaluated numerically to obtain a benchmark solution using the Laplace transforms coupled with the multiple collision expansion method. The benchmark solution is then used to check the accuracy of the multigroup approximation. Excellent agreement between continuous lethargy benchmarks and multigroup approximation is obtained.
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Frank, Martin [Verfasser]. "Partial Moment Models for Radiative Transfer / Martin Frank." Aachen : Shaker, 2005. http://d-nb.info/1186579609/34.
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Hart, Quinn James 1965. "Surface and aerosol models for use in radiative transfer codes." Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/277334.
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Absolute radiometric calibrations of Landsat 5 Thematic Mapper satellite are improved with the inclusion of a method to invert optical depth measurements to obtain an aerosol particle size distribution and a non-lambertian surface reflectance model. Also, a program is developed to improve speed and standardization of the entire calibration procedure. The inverted size distributions can predict radiances varying from the previous jungian distributions by as much as 5 percent, though the reduction in the estimated error is less than one percent. An empirical model for the surface reflection of White Sands using a two-degree polynomial fit as a function of scattering angle was employed. The model reduced estimated errors in radiance predictions by up to one percent. Satellite calibrations dating from October, 1984 are reprocessed using the improved methods and a linear estimation of satellite counts per unit radiance versus time since launch is determined.
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Bozzo, Alessio <1979>. "Atmospheric radiative transfer in multiple scattering conditions. Application to NWP models." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1874/1/bozzo_alessio_tesi.pdf.
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High spectral resolution radiative transfer (RT) codes are essential tools in the study of the radiative energy transfer in the Earth atmosphere and a support for the development of parameterizations for fast RT codes used in climate and weather prediction models. Cirrus clouds cover permanently 30% of the Earth's surface, representing an important contribution to the Earth-atmosphere radiation balance.
The work has been focussed on the development of the RT model LBLMS. The model, widely tested in the infra-red spectral range, has been extended to the short wave spectrum and it has been used in comparison with airborne and satellite measurements to study the optical properties of cirrus clouds. A new database of single scattering properties has been developed for mid latitude cirrus clouds. Ice clouds are treated as a mixture of ice crystals with various habits. The optical properties of the mixture are tested in comparison to radiometric measurements in selected case studies. Finally, a parameterization of the mixture for application to weather prediction and global circulation models has been developed. The bulk optical properties of ice crystals are parameterized as functions of the effective dimension of measured particle size distributions that are representative of mid latitude cirrus clouds. Tests with the Limited Area Weather Prediction model COSMO have shown the impact of the new parameterization with respect to cirrus cloud optical properties based on ice spheres.
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Bozzo, Alessio <1979>. "Atmospheric radiative transfer in multiple scattering conditions. Application to NWP models." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1874/.
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High spectral resolution radiative transfer (RT) codes are essential tools in the study of the radiative energy transfer in the Earth atmosphere and a support for the development of parameterizations for fast RT codes used in climate and weather prediction models. Cirrus clouds cover permanently 30% of the Earth's surface, representing an important contribution to the Earth-atmosphere radiation balance.
The work has been focussed on the development of the RT model LBLMS. The model, widely tested in the infra-red spectral range, has been extended to the short wave spectrum and it has been used in comparison with airborne and satellite measurements to study the optical properties of cirrus clouds. A new database of single scattering properties has been developed for mid latitude cirrus clouds. Ice clouds are treated as a mixture of ice crystals with various habits. The optical properties of the mixture are tested in comparison to radiometric measurements in selected case studies. Finally, a parameterization of the mixture for application to weather prediction and global circulation models has been developed. The bulk optical properties of ice crystals are parameterized as functions of the effective dimension of measured particle size distributions that are representative of mid latitude cirrus clouds. Tests with the Limited Area Weather Prediction model COSMO have shown the impact of the new parameterization with respect to cirrus cloud optical properties based on ice spheres.
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Imran, Hafiz Ali. "Remote Sensing Tools for Monitoring Grassland Plant Leaf Traits and Biodiversity." Doctoral thesis, Università degli studi di Trento, 2022. http://hdl.handle.net/11572/329592.
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Grasslands are one of the most important ecosystems on Earth, covering approximately one-third of the Earth’s surface. Grassland biodiversity is important as many services provided by such ecosystems are crucial for the human economy and well-being. Given the importance of grasslands ecosystems, in recent years research has been carried out on the potential to monitor them with novel remote sensing techniques. Improved detectors technology and novel sensors providing fine-scale hyperspectral imagery have been enabling new methods to monitor plant traits (PTs) and biodiversity.
The aims of the work were to study different approaches to monitor key grassland PTs such as Leaf Area Index (LAI) and biodiversity-related traits. The thesis consists of 3 parts: 1) Evaluating the performance of remote sensing methods to estimate LAI in grassland ecosystems, 2) Estimating plant biodiversity by using the optical diversity approach in grassland ecosystems, and 3) Investigating the relationship between PTs variability with alpha and beta diversity for the applicability of the optical diversity approach in a subalpine grassland of the Italian Alps
To evaluate the performance of remote sensing methods to estimate LAI, temporal and spatial observations of hyperspectral reflectance and LAI were analyzed at a grassland site in Monte Bondone, Italy (IT-MBo). In 2018, ground temporal observations of hyperspectral reflectance and LAI were carried out at a grassland site in Neustift, Austria (AT-NEU). To estimate biodiversity, in 2018 and 2019 a floristics survey was conducted to determine species composition and hyperspectral data were acquired at two grassland sites: IT-MBo and University of Padova’s Experimental Farm, Legnaro, Padua, Italy (IT-PD) respectively. Furthermore, in 2018, biochemistry analysis of the biomass samples collected from the grassland site IT-MBo was carried out to determine the foliar biochemical PTs variability.
The results of the thesis demonstrated that the grassland spectral response across different spectral regions (Visible: VIS, red-edge: RE, Near-infrared: NIR) showed to be both site-specific and scale-dependent. In the first part of the thesis, the performance of spectral vegetation indices (SVIs) based on visible, red-edge (RE), and NIR bands alongside SVIs solely based or NIR-shoulder bands (wavelengths 750 - 900 nm) was evaluated. A strong correlation (R2 > 0.8) was observed between grassland LAI and both RE and NIR-shoulder SVIs on a temporal basis, but not on a spatial basis. Using the PROSAIL Radiative Transfer Model (RTM), it was demonstrated that grassland structural heterogeneity strongly affects the ability to retrieve LAI, with high uncertainties due to structural and biochemical PTs co-variation.
In the second part, the applicability of the spectral variability hypothesis (SVH) was questioned and highlighted the challenges to use high-resolution hyperspectral images to estimate biodiversity in complex grassland ecosystems. It was reported that the relationship between biodiversity (Shannon, Richness, Simpson, and Evenness) and optical diversity metrics (Coefficient of variation (CV) and Standard deviation (SD)) is not consistent across plant communities. The results of the second part suggested that biodiversity in terms of species richness could be estimated by optical diversity metrics with an R2 = 0.4 at the IT-PD site where the grassland plots were artificially established and are showing a lower structure and complexity from the natural grassland plant communities. On the other hand, in the natural ecosystems at IT-MBo, it was more difficult to estimate biodiversity indices, probably due to structural and biochemical PTs co-variation. The effects of canopy non-vegetative elements (flowers and dead material), shadow pixels, and overexposed pixels on the relationship between optical diversity metrics and biodiversity indices were highlighted.
In the third part, we examined the relationship between PTs variability (at both local and community scales, measured by standard deviation and by the Euclidean distances of the biochemical and biophysical PTs respectively) and taxonomic diversity (both α-diversity and β-diversity, measured by Shannon’s index and by Jaccard dissimilarity index of the species, families, and functional groups percent cover respectively) in Monte Bondone, Trentino province, Italy. The results of the study showed that the PTs variability metrics at alpha scale were not correlated with α-diversity. However, the results at the community scale (β-diversity) showed that some of the investigated biochemical and biophysical PTs variations metrics were associated with β-diversity. The SVH approach was also tested to estimate β-diversity and we found that spectral diversity calculated by spectral angular mapper (SAM) showed to be a better proxy of biodiversity in the same ecosystem where the spectral diversity failed to estimate alpha diversity, this leading to the conclusion that the link between functional and species diversity may be an indicator of the applicability of optical sampling methods to estimate biodiversity.
The findings of the thesis highlighted that grassland structural heterogeneity strongly affects the ability to retrieve both LAI and biodiversity, with high uncertainties due to structural and biochemical PTs co-variation at complex grassland ecosystems. In this context, the uncertainties of satellite-based products (e.g., LAI) in monitoring grassland canopies characterized by either spatially or temporally varying structure need to be carefully taken into account. The results of the study highlighted that the poor performance of optical diversity proxies in estimating biodiversity in structurally heterogeneous grasslands might be due to the complex relationships between functional diversity and biodiversity, rather than the impossibility to detect functional diversity with spectral proxies.
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Smeltzer, Charles David. "In comparing radiative transfer and chemical transport models on OMI NO2 retrievals." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31677.
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Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2010.Committee Chair: Dr. Yuhang Wang; Committee Member: Dr. Greg Huey; Committee Member: Dr. Michael Chang. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Caunt, Stuart Edward. "Analytical and numerical models of accretion disks." Thesis, University of Newcastle Upon Tyne, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265485.
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Robinson, Tyler D., Jonathan J. Fortney, and William B. Hubbard. "Analytic Scattering and Refraction Models for Exoplanet Transit Spectra." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/627105.
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Observations of exoplanet transit spectra are essential to understanding the physics and chemistry of distant worlds. The effects of opacity sources and many physical processes combine to set the shape of a transit spectrum. Two such key processes-refraction and cloud and/or haze forward-scattering-have seen substantial recent study. However, models of these processes are typically complex, which prevents their incorporation into observational analyses and standard transit spectrum tools. In this work, we develop analytic expressions that allow for the efficient parameterization of forward-scattering and refraction effects in transit spectra. We derive an effective slant optical depth that includes a correction for forward-scattered light, and present an analytic form of this correction. We validate our correction against a full-physics transit spectrum model that includes scattering, and we explore the extent to which the omission of forward-scattering effects may bias models. Also, we verify a common analytic expression for the location of a refractive boundary, which we express in terms of the maximum pressure probed in a transit spectrum. This expression is designed to be easily incorporated into existing tools, and we discuss how the detection of a refractive boundary could help indicate the background atmospheric composition by constraining the bulk refractivity of the atmosphere. Finally, we show that opacity from Rayleigh scattering and collision-induced absorption will outweigh the effects of refraction for Jupiter-like atmospheres whose equilibrium temperatures are above 400-500 K.
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Müller, Laura [Verfasser]. "Investigation of moment models for population balance equations and radiative transfer equations / Laura Müller." München : Verlag Dr. Hut, 2019. http://d-nb.info/1176251287/34.
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Avila, Matías. "Nonlinear subgrid finite element models for low Mach number flows coupled with radiative heat transfer." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/285809.
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The general description of a fluid flow involves the solution of the compressible Navier-Stokes equations, a very complex problem whose mathematical structure is not well understood. It is widely accepted that these equations provide an accurate description of any problem in fluid mechanics which may present many different nonlinear physical mechanisms. Depending on the physics of the problem under consideration, different simplified models neglecting some physical mechanisms can be derived from asymptotic analysis. On the other hand, radiative heat transfer can strongly interact with convection in high temperature flows, and neglecting its effects may have significant consequences in the overall predictions. Problems as fire scenarios emphasized the need for an evaluation of the effect of radiative heat transfer. This work is directed to strongly thermally coupled low Mach number flows with radiative heat transfer.
The complexity of these mathematical problem makes their numerical solution very difficult. Despite the important difference in the treatment of the incompressibility, the low Mach number equations present the same mathematical structure as the incompressible Navier-Stokes equations, in the sense that the mechanical pressure is determined from the mass conservation constraint. Consequently the same type of numerical instabilities can be found, namely, the problem of compatibility conditions between the velocity and pressure finite element spaces, and the instabilities due to convection dominated flows. These instabilities can be avoided by the use of stabilization techniques. Many stabilization techniques used nowadays are based on the variational multiscale method, in which a decomposition of the approximating space into a coarse scale resolvable part and a fine scale subgrid part is performed. The modeling of the subgrid scale and its influence leads to a modified coarse scale problem providing stability. The quality of the final approximation (accuracy, efficiency) depends on the particular model.
The extension of these techniques to nonlinear and coupled problems is presented. The distinctive features of our approach are to consider the subscales as transient and to keep the scale splitting in all the nonlinear terms appearing in the finite element equations and in the subgrid scale model. The first ingredient permits to obtain an improved time discretization scheme(higher accuracy, better stability). The second ingredient permits to prove global conservation properties, being also responsible of the higher accuracy of the method. This ingredient is intimately related to the problem of thermal turbulence modeling from a strictly numerical point of view. The capability for the simulation of turbulent flows is a measure of the ability of modeling the effect of the subgrid flow structures over the coarser ones. The performance of the model in predicting the behavior of turbulent flows is demonstrated.
The radiation transport equation has been also approximated within the variational multiscale framework, the design and analysis of stabilized finite element methods is presented.La descripción general del movimiento de un flujo implica la solución de las ecuaciones de Navier-Stokes compresibles, un problema de muy compleja estructura matemática. Estas ecuaciones proporcinan una descripción detallada de cualquier problema en mecánica de fluidos, que puede presentar distintos mecanismos no lineales que interactúan entre si. En función de la física del problema que se esté considerando, pueden derivarse modelos simplificados de las ecuaciones de Navier-Stokes mediante analisis dimensional, que ignoran algunos fenómenos físicos. Por otro lado, la transferencia de calor por radiación puede interactuar con el movimiento de un fluido, e ignorar sus efectos puede tener consecuencias importantes en las predicciones del flujo. Problemas donde hay fuego implican la evaluacion del efecto del calor por radiación. El presente trabajo está dirigido a flujos a bajo número de Mach térmicamente acoplados, donde el calor por radiación afecta al flujo. Debido a la complejidad del problema matemático, la solución numérica es muy complicada. A pesar de las diferencia en el tratamiento de la incompresibilidad, las ecuaciones de flujo a bajo número de Mach poseen una estructura matemática similar a la de flujo incompresible, en el sentido que la presión mecánica se determina a partir de la ecuación de conservación de la masa. En consecuencia poseen el mismo tipo de inestabilidades numéricas, que son el problema de condiciones de compatibilidad entre los espacios de elementos finitos de velocidad y presión, y las inestabilidades debidas a flujos con convección dominante. Estas inestabilidades pueden evitarse mediante técnicas de estabilización numérica. Muchos métodos de estabilización utilizados hoy día se basan en el método de multiscalas variacionales, donde el espacio funcional de la solucion se divide en un espacio discreto y resolubre y un espacio infinito de subscalas. El modelado de las subescalas y su influencia modifican el problema discreto proporcionando estabilidad. La calidad de la aproximación numérica final (precisión, eficiencia) depende del modelo particular de subescalas. En este trabajo se extienden estas técnicas de estabilización a problemas no lineales y acoplados. Las características que distinguen a nuestra aproximación son considerar las subsecalas como transitorias y mantener la división de escalas en todos los términos no lineales que aparecen en las ecuaciones de elementros finitos y en las del modelo de subescalas. La primera característica permite obtener mayor precisión y mejor estabilidad en la solución, la segunda característica permite obtener esquemas donde las propiedades se conservan globalmente, y mayor precisión del método. El hecho de mantener la división de escalas en todos los términos no lineales está intimamemte relacionado con el modelado de turbulencia en flujos térmicamente acoplados desde un punto de vista estrictamente numérico. La capacidad de simulación de flujo turbulento es una medida de la habilidad de modelar el efecto de las estructuras de escala fina sobre las estructuras de escala gruesa. Se muestra en esta tesis el desempeño del método para de predecir flujo turbulento. La ecuación de transporte de radiación también se aproxima numéricamente en el marco de multiscala variacional. El diseño y análisis de este método se presenta en detalle en esta tesis
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Schlenz, Florian. "Coupled land surface and radiative transfer models for the analysis of passive microwave satellite observations." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-147374.
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Kattenborn, Teja [Verfasser], and S. [Akademischer Betreuer] Schmidtlein. "Linking Canopy Reflectance and Plant Functioning through Radiative Transfer Models / Teja Kattenborn ; Betreuer: S. Schmidtlein." Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/1174992263/34.
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Jones, David C. "Validation of scattering microwave radiative transfer models using an aircraft radiometer and ground-based radar." Thesis, University of Reading, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284065.
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Howett, Carly Jacqueline Amy. "Laboratory measurements of ammonia ice and ammonium hydrosulphide ice for use in Jovian radiative transfer models." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437054.
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Ekberg, Christopher. "Verification of the Incidence Angle Dependence within the Satellite Microwave Radiative Transfer Model, RadTb." Honors in the Major Thesis, University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/437.
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This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.Bachelors
Engineering and Computer Science
Computer Engineering
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Lee, Graham Kim Huat. "Glass rain : modelling the formation, dynamics and radiative-transport of cloud particles in hot Jupiter exoplanet atmospheres." Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/11740.
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The atmospheres of exoplanets are being characterised in increasing detail by observational facilities and will be examined with even greater clarity with upcoming space based missions such as the James Webb Space Telescope (JWST) and the Wide Field InfraRed Survey Telescope (WFIRST). A major component of exoplanet atmospheres is the presence of cloud particles which produce characteristic observational signatures in transit spectra and influence the geometric albedo of exoplanets. Despite a decade of observational evidence, the formation, dynamics and radiative-transport of exoplanet atmospheric cloud particles remains an open question in the exoplanet community. In this thesis, we investigate the kinetic chemistry of cloud formation in hot Jupiter exoplanets, their effect on the atmospheric dynamics and observable properties. We use a static 1D cloud formation code to investigate the cloud formation properties of the hot Jupiter HD 189733b. We couple a time-dependent kinetic cloud formation to a 3D radiative-hydrodynamic simulation of the atmosphere of HD 189733b and investigate the dynamical properties of cloud particles in the atmosphere. We develop a 3D multiple-scattering Monte Carlo radiative-transfer code to post-process the results of the cloudy HD 189733b RHD simulation and compare the results to observational results. We find that the cloud structures of the hot Jupiter HD 189733b are likely to be highly inhomogeneous, with differences in cloud particle sizes, number density and composition with longitude, latitude and depth. Cloud structures are most divergent between the dayside and nightside faces of the planet due to the instability of silicate materials on the hotter dayside. We find that the HD 189733b simulation in post-processing is consistent with geometric albedo observations of the planet. Due to the scattering properties of the cloud particles we predict that HD 189733b will be brighter in the upcoming space missions CHaracterising ExOPlanet Satellite (CHEOPS) bandpass compared to the Transiting Exoplanet Space Survey (TESS) bandpass.
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Haworth, Thomas James. "Radiation hydrodynamic models and simulated observations of radiative feedback in star forming regions." Thesis, University of Exeter, 2013. http://hdl.handle.net/10871/14465.
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This thesis details the development of the radiation transport code torus for radiation hydrodynamic applications and its subsequent use in investigating problems regarding radiative feedback. The code couples Monte Carlo photoionization with grid-based hydrodynamics and has the advantage that all of the features available to a dedicated radiation transport code are at its disposal in RHD applications. I discuss the development of the code, including the hydrodynamics scheme, the adaptive mesh refinement (AMR) framework and the coupling of radiation transport with hydrodynamics. Extensive testing of the resulting code is also presented. The main application involves the study of radiatively driven implosion (RDI), a mechanism where the expanding ionized region about a massive star impacts nearby clumps, potentially triggering star formation. Firstly I investigate the way in which the radiation field is treated, isolating the relative impacts of polychromatic and diffuse field radiation on the evolution of radiation hydrodynamic RDI models. I also produce synthetic SEDs, radio, Hα and forbidden line images of the bright rimmed clouds (BRCs) resulting from the RDI models, on which I perform standard diagnostics that are used by observers to obtain the cloud conditions. I test the accuracy of the diagnostics and show that considering the pressure difference between the neutral cloud and surrounding ionized layer can be used to infer whether or not RDI is occurring. Finally I use more synthetic observations to investigate the accuracy of molecular line diagnostics and the nature of line profiles of BRCs. I show that the previously unexplained lack of dominant blue-asymmetry (a blue-asymmetry is the expected signature of a collapsing cloud) in the line profiles of BRCs can be explained by the shell of material, swept up by the expanding ionized region, that drives into the cloud. The work in this thesis combines to help resolve the difficulties in understanding radiative feedback, which is a non–linear process that happens on small astrophysical timescales, by improving numerical models and the way in which they are compared with observations.
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Tse, Oliver [Verfasser]. "SPn-systems in Radiative Heat Transfer and Natural Convection-Radiation Models: Parameter Identification and Optimal Control / Oliver Tse." München : Verlag Dr. Hut, 2011. http://d-nb.info/101560496X/34.
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Mohan, Mahesh. "Polarimetric models of circumstellar discs including aggregate dust grains." Thesis, University of Hertfordshire, 2016. http://hdl.handle.net/2299/17229.
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The work conducted in this thesis examines the nature of circumstellar discs by investigating irradiance and polarization of scattered light. Two circumstellar discs are investigated. Firstly, H-band high contrast imaging data on the transitional disc of the Herbig Ae/Be star HD169142 are presented. The images were obtained through the polarimetric differential imaging (PDI) technique on the Very Large Telescope (VLT) using the adaptive optics system NACO. Our observations use longer exposure times, allowing us to examine the edges of the disc. Analysis of the observations shows distinct signs of polarization due to circumstellar material, but due to excessive saturation and adaptive optics errors further information on the disc could not be inferred. The HD169142 disc is then modelled using the 3D radiative transfer code Hyperion. Initial models were constructed using a two disc structure, however recent PDI has shown the existence of an annular gap. In addition to this, the annular gap is found not to be devoid of dust. This then led to the construction of a four-component disc structure. Estimates of the mass of dust in the gap (2:10x10⁻⁶ M⊙) are made as well as for the planet (≈1:53 x 10⁻⁵ M⊙ (0.016MJupiter)) suspected to be responsible for causing the gap. The predicted polarization was also estimated for the disc, peaking at 14 percent. The use of realistic dust grains (ballistic aggregate particles) in Monte Carlo code is also examined. The fortran code DDSCAT is used to calculate the scattering properties for aggregates which are used to replace the spherical grain models used by the radiative transfer code Hyperion. Currently, Hyperion uses four independent elements to de ne the scattering matrix, therefore the use of rotational averaging and a 50/50 percent population of grains and their enantiomers were explored to reduce the number of contributing scattering elements from DDSCAT. A python script was created to extract the scattering data from the DDSCAT output les and to apply a size distribution to the data. The second circumstellar disc investigated is the debris disc of the M dwarf star AU Mic. The disc was modelled, using the radiative transfer code Hyperion, based on F606W (HST) and JHK0-band (Keck II) scattered light observations and F606Wband polarized light observations. Initially, the disc is modelled as a two component structure using two grain types: compact silicate grains and porous dirty ice water. Both models are able to reproduce the observed SED and the F606W and H-band surface brightness pro les, but are unable to t the observed F606W degree of polarization. Therefore, a more complex/realistic grain model was examined (ballistic aggregate particles). In addition, recent millimetre observations suggest the existence of a planetesimal belt < 3 AU from the central star. This belt is included in the BAM2 model and was successful in fitting the observed SED, F606W and H-band surface brightness and F606W polarization. These results demonstrate the limitations of spherical grain models and indicate the importance of modelling more realistic dust grains.
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Palazzi, Elisa <1978>. "Retrieval of trace gases vertical profile in the lower atmosphere combining. Differential Optical Absorption Spectroscopy with radiative transfer models." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/983/1/Tesi_Palazzi_Elisa.pdf.
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The motivation for the work presented in this thesis is to retrieve profile
information for the atmospheric trace constituents nitrogen dioxide (NO2)
and ozone (O3) in the lower troposphere from remote sensing measurements.
The remote sensing technique used, referred to as Multiple AXis Differential
Optical Absorption Spectroscopy (MAX-DOAS), is a recent technique that
represents a significant advance on the well-established DOAS, especially for
what it concerns the study of tropospheric trace consituents.
NO2 is an important trace gas in the lower troposphere due to the fact that
it is involved in the production of tropospheric ozone; ozone and nitrogen
dioxide are key factors in determining the quality of air with consequences,
for example, on human health and the growth of vegetation. To understand
the NO2 and ozone chemistry in more detail not only the concentrations at
ground but also the acquisition of the vertical distribution is necessary. In
fact, the budget of nitrogen oxides and ozone in the atmosphere is determined
both by local emissions and non-local chemical and dynamical processes (i.e.
diffusion and transport at various scales) that greatly impact on their vertical
and temporal distribution: thus a tool to resolve the vertical profile
information is really important.
Useful measurement techniques for atmospheric trace species should fulfill
at least two main requirements. First, they must be sufficiently sensitive to
detect the species under consideration at their ambient concentration levels.
Second, they must be specific, which means that the results of the measurement
of a particular species must be neither positively nor negatively
influenced by any other trace species simultaneously present in the probed
volume of air. Air monitoring by spectroscopic techniques has proven to be
a very useful tool to fulfill these desirable requirements as well as a number
of other important properties. During the last decades, many such instruments
have been developed which are based on the absorption properties of
the constituents in various regions of the electromagnetic spectrum, ranging
from the far infrared to the ultraviolet. Among them, Differential Optical
Absorption Spectroscopy (DOAS) has played an important role.
DOAS is an established remote sensing technique for atmospheric trace
gases probing, which identifies and quantifies the trace gases in the atmosphere
taking advantage of their molecular absorption structures in the near
UV and visible wavelengths of the electromagnetic spectrum (from 0.25 μm
to 0.75 μm). Passive DOAS, in particular, can detect the presence of a trace
gas in terms of its integrated concentration over the atmospheric path from
the sun to the receiver (the so called slant column density). The receiver
can be located at ground, as well as on board an aircraft or a satellite platform.
Passive DOAS has, therefore, a flexible measurement configuration
that allows multiple applications.
The ability to properly interpret passive DOAS measurements of atmospheric
constituents depends crucially on how well the optical path of light
collected by the system is understood. This is because the final product of
DOAS is the concentration of a particular species integrated along the path
that radiation covers in the atmosphere. This path is not known a priori and
can only be evaluated by Radiative Transfer Models (RTMs). These models
are used to calculate the so called vertical column density of a given trace
gas, which is obtained by dividing the measured slant column density to the
so called air mass factor, which is used to quantify the enhancement of the
light path length within the absorber layers.
In the case of the standard DOAS set-up, in which radiation is collected
along the vertical direction (zenith-sky DOAS), calculations of the air mass
factor have been made using “simple” single scattering radiative transfer
models. This configuration has its highest sensitivity in the stratosphere,
in particular during twilight. This is the result of the large enhancement in
stratospheric light path at dawn and dusk combined with a relatively short
tropospheric path.
In order to increase the sensitivity of the instrument towards tropospheric
signals, measurements with the telescope pointing the horizon (offaxis
DOAS) have to be performed. In this circumstances, the light path in the
lower layers can become very long and necessitate the use of radiative transfer
models including multiple scattering, the full treatment of atmospheric
sphericity and refraction.
In this thesis, a recent development in the well-established DOAS technique
is described, referred to as Multiple AXis Differential Optical Absorption
Spectroscopy (MAX-DOAS). The MAX-DOAS consists in the simultaneous
use of several off-axis directions near the horizon: using this configuration,
not only the sensitivity to tropospheric trace gases is greatly improved,
but vertical profile information can also be retrieved by combining the simultaneous
off-axis measurements with sophisticated RTM calculations and
inversion techniques.
In particular there is a need for a RTM which is capable of dealing with
all the processes intervening along the light path, supporting all DOAS geometries
used, and treating multiple scattering events with varying phase
functions involved. To achieve these multiple goals a statistical approach
based on the Monte Carlo technique should be used. A Monte Carlo RTM
generates an ensemble of random photon paths between the light source and
the detector, and uses these paths to reconstruct a remote sensing measurement.
Within the present study, the Monte Carlo radiative transfer
model PROMSAR (PROcessing of Multi-Scattered Atmospheric Radiation)
has been developed and used to correctly interpret the slant column densities
obtained from MAX-DOAS measurements.
In order to derive the vertical concentration profile of a trace gas from
its slant column measurement, the AMF is only one part in the quantitative
retrieval process. One indispensable requirement is a robust approach to
invert the measurements and obtain the unknown concentrations, the air
mass factors being known. For this purpose, in the present thesis, we have
used the Chahine relaxation method.
Ground-based Multiple AXis DOAS, combined with appropriate radiative
transfer models and inversion techniques, is a promising tool for atmospheric
studies in the lower troposphere and boundary layer, including the retrieval of
profile information with a good degree of vertical resolution. This thesis has
presented an application of this powerful comprehensive tool for the study of
a preserved natural Mediterranean area (the Castel Porziano Estate, located
20 km South-West of Rome) where pollution is transported from remote
sources.
Application of this tool in densely populated or industrial areas is beginning
to look particularly fruitful and represents an important subject for future
studies.
23
Palazzi, Elisa <1978>. "Retrieval of trace gases vertical profile in the lower atmosphere combining. Differential Optical Absorption Spectroscopy with radiative transfer models." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/983/.
Full textAbstract:
The motivation for the work presented in this thesis is to retrieve profile
information for the atmospheric trace constituents nitrogen dioxide (NO2)
and ozone (O3) in the lower troposphere from remote sensing measurements.
The remote sensing technique used, referred to as Multiple AXis Differential
Optical Absorption Spectroscopy (MAX-DOAS), is a recent technique that
represents a significant advance on the well-established DOAS, especially for
what it concerns the study of tropospheric trace consituents.
NO2 is an important trace gas in the lower troposphere due to the fact that
it is involved in the production of tropospheric ozone; ozone and nitrogen
dioxide are key factors in determining the quality of air with consequences,
for example, on human health and the growth of vegetation. To understand
the NO2 and ozone chemistry in more detail not only the concentrations at
ground but also the acquisition of the vertical distribution is necessary. In
fact, the budget of nitrogen oxides and ozone in the atmosphere is determined
both by local emissions and non-local chemical and dynamical processes (i.e.
diffusion and transport at various scales) that greatly impact on their vertical
and temporal distribution: thus a tool to resolve the vertical profile
information is really important.
Useful measurement techniques for atmospheric trace species should fulfill
at least two main requirements. First, they must be sufficiently sensitive to
detect the species under consideration at their ambient concentration levels.
Second, they must be specific, which means that the results of the measurement
of a particular species must be neither positively nor negatively
influenced by any other trace species simultaneously present in the probed
volume of air. Air monitoring by spectroscopic techniques has proven to be
a very useful tool to fulfill these desirable requirements as well as a number
of other important properties. During the last decades, many such instruments
have been developed which are based on the absorption properties of
the constituents in various regions of the electromagnetic spectrum, ranging
from the far infrared to the ultraviolet. Among them, Differential Optical
Absorption Spectroscopy (DOAS) has played an important role.
DOAS is an established remote sensing technique for atmospheric trace
gases probing, which identifies and quantifies the trace gases in the atmosphere
taking advantage of their molecular absorption structures in the near
UV and visible wavelengths of the electromagnetic spectrum (from 0.25 μm
to 0.75 μm). Passive DOAS, in particular, can detect the presence of a trace
gas in terms of its integrated concentration over the atmospheric path from
the sun to the receiver (the so called slant column density). The receiver
can be located at ground, as well as on board an aircraft or a satellite platform.
Passive DOAS has, therefore, a flexible measurement configuration
that allows multiple applications.
The ability to properly interpret passive DOAS measurements of atmospheric
constituents depends crucially on how well the optical path of light
collected by the system is understood. This is because the final product of
DOAS is the concentration of a particular species integrated along the path
that radiation covers in the atmosphere. This path is not known a priori and
can only be evaluated by Radiative Transfer Models (RTMs). These models
are used to calculate the so called vertical column density of a given trace
gas, which is obtained by dividing the measured slant column density to the
so called air mass factor, which is used to quantify the enhancement of the
light path length within the absorber layers.
In the case of the standard DOAS set-up, in which radiation is collected
along the vertical direction (zenith-sky DOAS), calculations of the air mass
factor have been made using “simple” single scattering radiative transfer
models. This configuration has its highest sensitivity in the stratosphere,
in particular during twilight. This is the result of the large enhancement in
stratospheric light path at dawn and dusk combined with a relatively short
tropospheric path.
In order to increase the sensitivity of the instrument towards tropospheric
signals, measurements with the telescope pointing the horizon (offaxis
DOAS) have to be performed. In this circumstances, the light path in the
lower layers can become very long and necessitate the use of radiative transfer
models including multiple scattering, the full treatment of atmospheric
sphericity and refraction.
In this thesis, a recent development in the well-established DOAS technique
is described, referred to as Multiple AXis Differential Optical Absorption
Spectroscopy (MAX-DOAS). The MAX-DOAS consists in the simultaneous
use of several off-axis directions near the horizon: using this configuration,
not only the sensitivity to tropospheric trace gases is greatly improved,
but vertical profile information can also be retrieved by combining the simultaneous
off-axis measurements with sophisticated RTM calculations and
inversion techniques.
In particular there is a need for a RTM which is capable of dealing with
all the processes intervening along the light path, supporting all DOAS geometries
used, and treating multiple scattering events with varying phase
functions involved. To achieve these multiple goals a statistical approach
based on the Monte Carlo technique should be used. A Monte Carlo RTM
generates an ensemble of random photon paths between the light source and
the detector, and uses these paths to reconstruct a remote sensing measurement.
Within the present study, the Monte Carlo radiative transfer
model PROMSAR (PROcessing of Multi-Scattered Atmospheric Radiation)
has been developed and used to correctly interpret the slant column densities
obtained from MAX-DOAS measurements.
In order to derive the vertical concentration profile of a trace gas from
its slant column measurement, the AMF is only one part in the quantitative
retrieval process. One indispensable requirement is a robust approach to
invert the measurements and obtain the unknown concentrations, the air
mass factors being known. For this purpose, in the present thesis, we have
used the Chahine relaxation method.
Ground-based Multiple AXis DOAS, combined with appropriate radiative
transfer models and inversion techniques, is a promising tool for atmospheric
studies in the lower troposphere and boundary layer, including the retrieval of
profile information with a good degree of vertical resolution. This thesis has
presented an application of this powerful comprehensive tool for the study of
a preserved natural Mediterranean area (the Castel Porziano Estate, located
20 km South-West of Rome) where pollution is transported from remote
sources.
Application of this tool in densely populated or industrial areas is beginning
to look particularly fruitful and represents an important subject for future
studies.
24
Erbas, Cihan. "Validation of remotely-sensed soil moisture observations for bare soil at 1.4 GHz a quantitative approach through radiative transfer models to characterize abrupt transitions caused by a ponding event in an agricultural field, modifications to the radiative transfer models, and a mobile ground-based system /." [Ames, Iowa : Iowa State University], 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3371777.
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Schlenz, Florian [Verfasser], and Wolfram [Akademischer Betreuer] Mauser. "Coupled land surface and radiative transfer models for the analysis of passive microwave satellite observations / Florian Schlenz. Betreuer: Wolfram Mauser." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2012. http://d-nb.info/1025821963/34.
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Walker, Christina H. "Monte Carlo radiation transfer studies of protoplanetary environments." Thesis, University of St Andrews, 2007. http://hdl.handle.net/10023/218.
Full textAbstract:
Monte Carlo radiation transfer provides an efficient modelling tool for probing the dusty local environment of young stars. Within this thesis, such theoretical models are used to study the disk structure of objects across the mass spectrum - young low mass Brown Dwarfs, solar mass T-Tauri stars, intermediate mass Herbig Ae stars, and candidate B-stars with massive disks. A Monte Carlo radiation transfer code is used to model images and photometric data in the UV - mm wavelength range. These models demonstrate how modelling techniques have been updated in an attempt to reduce the number of unknown parameters and extend the diversity of objects that can be studied.
27
Hachinger, Stephan [Verfasser], Wolfgang [Akademischer Betreuer] Hillebrandt, and Wolfram [Akademischer Betreuer] Weise. "Analysis of spectra of Type I Supernovae with radiative transfer models / Stephan Hachinger. Gutachter: Wolfgang Hillebrandt ; Wolfram Weise. Betreuer: Wolfgang Hillebrandt." München : Universitätsbibliothek der TU München, 2011. http://d-nb.info/1014329744/34.
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Petkova, Maya Atanasova. "Cloudy with a chance of starlight : coupling of smoothed particle hydrodynamics and Monte Carlo radiative transfer for the study of ionising stellar feedback." Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/16557.
Full textAbstract:
Ionising radiation is present in a variety of astrophysical problems, and it is particularly important for shaping the process of star formation in molecular clouds, containing hot, high-mass stars. In order to account for the effects of ionising radiation within numerical models of star formation, we need to combine a hydrodynamics method with a radiative transfer method and obtain a radiation hydrodynamics scheme (RHD). In this thesis I achieve live radiation hydrodynamics by coupling the Smoothed Particle Hydrodynamics (SPH) code Phantom with the Monte Carlo Radiative Transfer (MCRT) code CMacIonize. Since SPH is particle-based and MCRT is grid-based, I construct an unstructured, Voronoi grid in order to establish a link between the two codes. In areas with large density gradients, a Voronoi grid based purely on the SPH particle positions achieves insufficient resolution, and therefore I propose a novel algorithm for inserting a small number of additional grid cells to improve the local resolution. Furthermore, the MCRT calculations require the knowledge of an average density for each Voronoi cell. To address this, I develop an analytic density mapping from SPH to a Voronoi grid, by deriving an expression for the integrals of a series of kernel functions over the volume of a random polyhedron. Finally, I demonstrate the validity of the live RHD through the benchmark test of D-type expansion of an H II region, where good agreement is shown with the existing literature. The RHD implementation is then used to perform a proof-of-concept simulation of a collapsing cloud, which produces high-mass stars and is subsequently partially ionised by them. The presented code is a valuable tool for future star formation studies, and it can be used for modelling a broad range of additional astronomical problems involving ionising radiation and hydrodynamics.
29
Robertson, Scott James. "Hawking radiation in dispersive media." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/1900.
Full textAbstract:
Hawking radiation, despite its presence in theoretical physics for over thirty years, remains elusive and undetected. It also suffers, in its original context of gravitational black holes, from conceptual difficulties. Of particular note is the trans-Planckian problem, which is concerned with the apparent origin of the radiation in absurdly high frequencies. In order to gain better theoretical understanding and, it is hoped, experimental verification of Hawking radiation, much study is being devoted to systems which model the spacetime geometry of black holes, and which, by analogy, are also thought to emit Hawking radiation. These analogue systems typically exhibit dispersion, which regularizes the wave behaviour at the horizon but does not lend itself well to analytic treatment, thus rendering Hawking’s prediction less secure. A general analytic method for dealing with Hawking radiation in dispersive systems has proved difficult to find. This thesis presents new numerical and analytic results for Hawking emission spectra in dispersive systems. It examines two black-hole analogue systems: it begins by introducing the well-known acoustic model, presenting some original results in that context; then, through analogy with the acoustic model, goes on to develop the lesser-known fibre-optical model. The following original results are presented in the context of both of these models: • an analytic expression for the low-frequency temperature is found for a hyperbolic tangent background profile, valid in the entire parameter space; it is well-known that the spectrum is approximately thermal at low frequencies, but a universally valid expression for the corresponding temperature is an original development; • an analytic expression for the spectrum, valid over almost the entire frequency range, when the velocity profile parameters lie in the regime where the low-frequency temperature is given by the Hawking prediction; previous work has focused on the low-frequency thermal spectrum and the characterization of the deviations from thermality, rather than a single analytic expression; and • a new unexplored regime where no group-velocity horizon exists is examined; the Hawking spectra are found to be non-zero here, but also highly non-thermal, and are found, in the limit of small deviations, to vary with the square of the maximum deviation; the analytic expression for the case with a horizon is found to carry over to this new regime, with appropriate modifications. Furthermore, the thesis examines the results of a classical frequency-shifting experiment in the context of fibre-optical horizons. The theory of this process is presented for both a constant-velocity and a constantly-decelerating pulse, the latter case taking account of the Raman effect. The resulting spectra are at least qualititively explained, but there is a discrepancy between theory and experiment that has not yet been accounted for.
30
Hamilton, Steven. "A Time-Dependent Slice Balance Method for High-Fidelity Radiation Transport Computations." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14608.
Full textAbstract:
A general finite difference discretization of the time-dependent radiation transport equation is developed around the framework of an existing steady-state three dimensional radiation transport solver based on the slice-balance approach. Three related algorithms are outlined within the general finite difference scheme: an explicit, an implicit, and a semi-implicit approach. The three algorithms are analyzed with respect to the discretizations of each element of the phase space in the transport solver. The explicit method, despite its small computational cost per time step, is found to be unsuitable for many purposes due to its inability to accurately handle rapidly varying solutions. The semi-implicit method is shown to produce results nearly as reliable as the fully implicit solver, while requiring significantly less computational effort.
31
Zernickel, Alexander [Verfasser], Peter [Akademischer Betreuer] Schilke, and Volker [Akademischer Betreuer] Ossenkopf. "Submm Observations of Massive Star Formation in the Giant Molecular Cloud NGC 6334 : Gas Kinematics with Radiative Transfer Models / Alexander Zernickel. Gutachter: Peter Schilke ; Volker Ossenkopf." Köln : Universitäts- und Stadtbibliothek Köln, 2015. http://d-nb.info/1072500493/34.
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Pattnaik, Aliva. "Parallel Performance Analysis of The Finite Element-Spherical Harmonics Radiation Transport Method." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14069.
Full textAbstract:
In this thesis, the parallel performance of the finite element-spherical harmonics (FE-PN) method implemented in the general-purpose radiation transport code EVENT is studied both analytically and empirically. EVENT solves the coupled set of space-angle discretized FE-PN equations using a parallel block-Jacobi domain decomposition method. As part of the analytical study, the thesis presents complexity results for EVENT when solving for a 3D criticality benchmark radiation transport problem in parallel. The empirical analysis is concerned with the impact of the main algorithmic factors affecting performance. Firstly, EVENT supports two solution strategies, namely MOD (Moments Over Domains) and DOM (Domains Over Moments), to solve the transport equation in parallel. The two strategies differ in the way they solve the multi-level space-angle coupled systems of equations. The thesis presents empirical evidence of which of the two solution strategies is more efficient. Secondly, different preconditioners are used in the Preconditioned Conjugate Gradient (PCG) inside EVENT. Performance of EVENT is compared when using three preconditioners, namely diagonal, SSOR(Symmetric Successive Over-Relaxation) and ILU. The other two factors, angular and spatial resolutions of the problem affect both the performance and precision of EVENT. The thesis presents comparative results on EVENTs performance as these two resolutions are increased.
From the empirical performance study of EVENT, a bottleneck is identified that limits the improvement in performance as number of processors used by EVENT is increased. In some experiments, it is observed that uneven assignment of computational load among processors causes a significant portion of the total time being spent in synchronization among processors. The thesis presents two indicators that identify when such inefficiency occur; and in such a case, a load rebalancing strategy is applied that computes a new partition of the problem so that each partition corresponds to equal amount of computational load.
33
Ventress, Lucy Jane. "Atmospheric Sounding using IASI." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:7ad570a3-35ad-4d98-93bb-7e1549afcdcd.
Full textAbstract:
The Infrared Atmospheric Sounding Interferometer (IASI) provides atmospheric observations with high spectral resolution and its data have been shown to have a significant positive impact on global Numerical Weather Prediction (NWP) and trace gas retrievals. A fundamental component of the retrieval of atmospheric composition is the radiative transfer model used to simulate the observations. An accurate representation of the expected emission spectrum measured by the satellite is essential given that differences in the reproduced atmospheric spectra propagate through a retrieval procedure and produce an altered estimate of the atmospheric state. The importance of the assumptions within the forward model are discussed and it is established that in the simulation of spectra from satellite-borne instruments the choice of the model parameters can have a large impact upon the resulting output. These assumptions are explored in the context of the Reference Forward Model (RFM), which is further configured to optimise its output for simulating the IASI spectrum in the troposphere. In order to ascertain the consistency of different radiative transfer models, comparisons are carried out between the RFM and the Radiative Transfer model for TOVS (RTTOV) in order to quantify any discrepancies in the reproduction of IASI measurements. Good agreement is shown across the majority of the spectrum, with exceptions caused by CO2 line mixing effects and the H2O continuum. Alongside model comparisons, the RFM is validated against real IASI measurements. Being a Fourier Transform Spectrometer, there are a large number of channels available from the IASI instrument, which leads to a very large quantity of data. However, this can lead to problems within retrievals and data assimilation. Choosing an optimal subset of the channels is an established method to reduce the amount of data; maintaining the information contained within it whilst eliminating spectral regions with large uncertainties. The method currently used at the UK Met Office to select their spectral channels is re-assessed and a modified method is presented that improves upon the modelling of spectrally correlated errors.
34
Galarça, Marcelo Moraes. "Modelagem espectral da radiação em processos de combustão baseada no método do número de onda acumulado." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2010. http://hdl.handle.net/10183/26539.
Full textAbstract:
O trabalho apresenta uma modificação do modelo do número de onda cumulativo (CW – Cumulative Wavenumber) para atender ao balanço de energia na determinação da transferência radiante de gases participantes não uniformes. De um modo geral, o modelo CW fornece resultados que se mostram precisos para o divergente do fluxo de calor radiante (ou taxa volumétrica de geração de energia) quando comparados à solução benchmark (integração linhapor- linha). No entanto, conforme é apresentado nesta pesquisa, uma hipótese importante feita pelo modelo o torna não conservativo e, não garantindo o balanço de energia radiante quando um meio não uniforme é considerado. Como conseqüência, o fluxo de calor radiante pode apresentar desvios consideráveis em relação à solução exata. O modelo do número de onda cumulativo modificado (CWM) foi desenvolvido de forma a manter o mesmo valor para a taxa volumétrica de geração de energia, mas satisfazendo ao balanço de energia radiante. O modelo CWM é aplicado juntamente com o método das ordenadas discretas para resolver a transferência de calor radiante em sistemas unidimensionais formados por placas planas infinitas e paralelas, contendo camadas uniformes e não uniformes de gases típicos da combustão de metano ou óleo combustível. As paredes são negras para a radiação térmica. A aquisição de dados das linhas de absorção espectrais é feita pela utilização dos bancos de dados HITRAN e HITEMP. São apresentados os bancos de dados, bem como a forma em que é efetuada a extração destes e, posteriormente, a elaboração dos espectros de absorção das espécies químicas. São analisados meios uniformes (isotérmicos e homogêneos) primeiramente, evidenciando que o modelo original (CW) não apresenta problemas nesses casos. Posteriormente, meios não uniformes (nãoisotérmicos e homogêneos; ou não-isotérmicos e não homogêneos) são avaliados. Os resultados para ambos os modelos, CW e CWM, são comparados com a solução linha-por-linha (LBL). Casos com diferentes perfis de temperatura e concentração da espécie química são considerados. A solução a partir da nova metodologia se apresentou mais dispendiosa computacionalmente devido ao acréscimo de novos passos iterativos. Os resultados mostram que o CWM leva a resultados mais precisos para o fluxo de calor radiante, satisfazendo ao balanço de energia com um desvio que se deve principalmente à discretização espacial da equação de transporte radiante.This work presents a modification of the cumulative wavenumber (CW) method to determine the radiative transfer in non-uniform participating gases to enforce the radiative energy balance to be satisfied. In particular, the CW model leads to results for the divergent radiative heat flux (or radiative volumetric heat source) that proved accurate in comparison to the benchmark solution ( LBL integration) for non-isothermal medium. However, as will be shown in this work, one important assumption of the method prevents it of satisfying the radiative energy balance when a non uniform medium is considered. As consequence, the radiative heat flux can present considerable deviation of the correct solution. The modified cumulative wavenumber (CWM) model was developed to keep the same value of the radiative volumetric heat source, but also to satisfy the radiative energy balance. The CWM model is applied together with the discrete ordinates method to solve the radiation heat transfer in a one-dimentional slab containing a uniform/non-uniform layer of typical gases from the methane or fuel oil combustion. The walls are black for the thermal radiation. The HITRAN and HITEMP are used to extract the spectral lines information that is required for modeling. The database are briefly presented as well as the procedure that is used to extract the data and the spectra drawing. Firstly, uniform media (isothermal and homogeneous) are analyzed proving that the original model (CW) presents accurate results in those cases. Next, non-uniform media (non-isothermal and homogeneous; or non-isothermal and non-homogeneous) are taken into account. The results of both the CW and the CWM modeling are compared to the benchmark line-by-line (LBL) integration. Different temperature and concentration profiles are considered. The solution obtained from the new model presents an increase in the computational time due to the insertion of new iterative loops. The results show that the CWM leads to accurate estimation of both the radiative heat flux and volumetric heat source, satisfying the radiative energy balance with an error that is mostly due to the spatial discretization of the radiative transfer equation.
35
Ayliffe, Benjamin A. "Giant planet formation and migration." Thesis, University of Exeter, 2009. http://hdl.handle.net/10036/85873.
Full textAbstract:
This thesis describes efforts to improve the realism of numerical models of giant planet formation and migration in an attempt to better understand these processes. A new approach has been taken to the modelling of accretion, designed to mimic reality by allowing gas to accumulate upon a protoplanetary surface. Implementing this treatment in three-dimensional self-gravity radiation hydrodynamics calculations provides an excellent model for planet growth, allowing an exploration of the factors that affect accretion. Moreover, these calculations have also been extended to investigate the migration of protoplanets through their parent discs as they grow. When focusing on the growth of non-migrating protoplanets, the models are performed using small sections of disc, enabling excellent resolution right down to the core; gas structures and flow can be resolved on scales from ~ 10^4 to 10^11 metres. Using radiative transfer, these models reveal the importance of opacity in determining the accretion rates. For the low mass protoplanets, equivalent in mass to a giant planet core (~ 10 M⊕), the accretion rates were found to increase by up to an order of magnitude for a factor of 100 reduction in the grain opacity of the parent circumstellar disc. However, even these low opacities lead to growth rates that are an order of magnitude slower than those obtained in locally-isothermal conditions. For high mass protoplanets (>~ 100M⊕), the accretion rates show very little dependence upon opacity. Nevertheless, the rates obtained using radiative transfer are still lower than those obtained in locally-isothermal models by a factor of ~2, due to the release of accretion energy as heat. Only high mass protoplanets are found to be capable of developing circumplanetary discs, and this ability is dependent upon the opacity, as are the scaleheights of such discs. However, their radial extents were found to be independent of the opacity and the protoplanet mass, all reaching ≈ RH/3, inline with analytic predictions. Migration is investigated using global models, ensuring a self-consistently evolved disc. Using locally-isothermal calculations, it was found that the capture radius of an accreting sink particle, used to model a protoplanet without a surface, must be small (<< RH) to yield migration timescales consistent with linear theory of Type I migration. In the low mass regime of Type I migration, accreting sinks with such small radii yield timescales consistent with those models in which a protoplanetary surface is used. However, for high mass protoplanets, undergoing Type II migration, the surface treatment leads to faster rates of migration, indicating the importance of a realistic accretion model. Using radiative transfer, with high opacities, leads to a factor of ~ 3 increase in the migration timescale of the lowest mass protoplanets, improving their chances of survival. As suitable gas giant progenitors, their survival is key to understanding the growth of giant planets. An unexpected result of the radiative transfer was a reduction in the migration timescale of high mass planets. This appears to be a result of the less thoroughly evacuated gaps created by planets in non-locally-isothermal discs, which affects the corotation torque.
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Hall, Cassandra. "Using numerical simulations to identify observational signatures of self-gravitating protostellar discs." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/29585.
Full textAbstract:
In this thesis, I study numerical and semi-analytical models of self-gravitating protostellar discs, with the aim of furthering our understanding of the role of disc-self gravity in planet formation. At the time of writing, the ALMA era of observational astronomy is upon us. Therefore, I place my research into this context with synthetic images of both numerical and semi-analytical models. I begin with an examination into the apparent lack of convergence, with increasing resolution, of the fragmentation boundary in Smoothed Particle Hydrodynamics (SPH) simulations of a protostellar disc. I run a suite of SPH with different numerical implementations, and find that even very similar implementations can fundamentally change the final answer. I analyse a suite of SPH simulations that fragment to form gravitationally bound objects, with the motivation of informing future population synthesis model development. I find that fragment-fragment and fragment-disc interaction dominates the orbital evolution of the system even at very early times, and any attempt to produce a population of objects from the gravitational instability process must include these interactions. Before a disc fragments, it will go through a self-gravitating phase. If the disc cools globally on a timescale such that it is balanced by heating due to gravitational stresses, the disc will be in a state of quasi-equilibrium. So long as the disc mass is sufficiently low, and spirals are sufficiently tightly wound, then angular momentum transport can be described by the local approximation, for which there is an analytical description. Using this analytical description, I develop an existing 1D model into 3D, and examine a wide range of parameter space for which disc self-gravity produces significant non-axisymmetry. Using radiative transfer calculations coupled with synthetic observations, I determine that there is a very narrow range of parameter space in which a disc will have sufficiently large gravitational stresses so as to produce detectable spirals, but the stresses not be so large as to cause the disc to fragment. By developing a simple analytical prescription for dust, I show that this region of parameter space can be broadened considerably. However, it requires grains that are large enough to become trapped by pressure maxima in the disc, so I conclude that if self-gravitating spiral arms are detected in the continuum, it is likely that at least some grain growth has taken place.
37
Jiang, Jingyi. "Retrieving leaf and canopy characteristics from their radiative properties using physically based models : from laboratory to satellite observations Estimation of leaf traits from reflectance measurements: comparison between methods based on vegetation indices and several versions of the PROSPECT model a model of leaf optical properties accounting for the differences between upper and lower faces Speeding up 3D radiative transfer simulations: a physically based approximation of canopy reflectance dependency on wavelength, leaf biochemical composition and soil reflectance Effective GAI for crops is best estimated from reflectance observations as compared to GAI and LAI Optimal learning for GAI and chlorophyll estimation from 1D and 3D radiative transfer model inversion: the case of wheat and maize crops observed by Sentinel2." Thesis, Avignon, 2019. http://www.theses.fr/2019AVIG0708.
Full textAbstract:
La mesure des caractéristiques des feuilles et du couvert végétal par télédétection est un moyen efficace et non destructif d’effectuer un suivi des cultures, que ce soit pour la prise de décision dans la gestion d’itinéraires techniques an agriculture de précision ou pour le phénotypage au champ pour améliorer l'efficacité de la sélection variétale. Grâce à l’augmentation de la puissance de calcul des machines et à la disponibilité croissante d'images à haute résolution spatiale, les méthodes d’estimation peuvent maintenant bénéficier de simulations plus précises des modèles de transfert radiatif (RT) dans la végétation. L'objectif de ce travail est de proposer et d'évaluer des moyens efficaces pour estimer les caractéristiques des feuilles et du couvert végétal à partir d'observations rapprochées ou de télédétection en utilisant des modèles RT basés sur une description réaliste de la structure des feuilles et du couvert. Au niveau des feuilles, nous avons d'abord évalué la capacité des différentes versions du modèle PROSPECT à estimer des variables biochimiques comme la chlorophylle (Cab), la teneur en eau et en matière sèche. Nous avons ensuite proposé le modèle FASPECT pour décrire les différences de propriétés optiques entre les faces supérieure et inférieure des feuilles en considérant un système à quatre couches. Après avoir étalonné les coefficients d'absorption spécifiques des principaux constituants de la feuille, nous avons validé FASPECT sur 8 jeux de données. Nous avons montré que les spectres de réflectance et de transmittance des deux faces sont simulés avec une très bonne précision, et même meilleure que PROSPECT pour la face supérieure. De même, en mode inverse, les performances d'estimation de la teneur en matière sèche sont considérablement améliorées avec FASPECT par rapport à PROSPECT, et restent du même ordre de grandeur pour la chlorophylle et l’eau. Au niveau du couvert végétal, nous avons utilisé le simulateur de rendu physique réaliste LuxCoreRender pour calculer le transfert radiatif à partir d'une description 3D de l’architecture de la culture. Nous avons d’abord vérifié ses bonnes performances par comparaison aux modèles 3D les plus récents en utilisant ROMC (RAMI On Line Model Checker). Afin d’accélérer les simulations, nous avons développé une méthode qui repose sur l’utilisation d’un nombre limité de propriétés optiques du sol et des feuilles. Pour estimer les variables d'état du couvert végétal (indice de surface verte, GAI, contenu en chlorophylle du couvert (CCC) ou des feuilles (Cab), nous avons ensuite entrainé des algorithmes d’apprentissage automatique à partir de bases de données « culture spécifique » simulées avec LuxCoreRender pour le blé et le maïs et d’une base de données générique simulée avec le modèle 1D PROSAIL de transfert radiatif. Les résultats sur des simulations et sur des données in situ combinés aux images SENTINEL2 ont montré que les algorithmes spécifiques aux cultures surpassent les algorithmes génériques pour les trois variables, en particulier lorsque la structure du couvert s’éloigne de l'hypothèse 1D du milieu turbide, comme dans le cas du maïs où la structure en rang domine pendant toute une partie de la saison de croissanceMeasuring leaf and canopy characteristics from remote sensing acquisitions is an effective and non destructive way to monitor crops both for decision making within the smart agriculture practices or for phenotyping under field conditions to improve the selection efficiency. With the advancement of computer computing power and the increasing availability of high spatial resolution images, retrieval methods can now benefit from more accurate simulations of the Radiative Transfer (RT) models within the vegetation. The objective of this work is to propose and evaluate efficient ways to retrieve leaf and canopy characteristics from close and remote sensing observations by using RT models based on a realistic description of the leaf and canopy structures. At the leaf level, we first evaluated the ability of the different versions of the PROSPECT model to estimate biochemical variables like chlorophyll (Cab), water and dry matter content. We then proposed the FASPECT model to describe the optical properties differences between the upper and lower leaf faces by considering a four-layer system. After calibrating the specific absorption coefficients of the main absorbing material, we validated FASPECT against eight measured ground datasets. We showed that FASPECT simulates accurately the reflectance and transmittance spectra of the two faces and overperforms PROSPECT for the upper face measurements. Moreover, in the inverse mode, the dry matter content estimation is significantly improved with FASPECT as compared to PROSPECT. At the canopy level, we used the physically based and unbiased rendering engine, LuxCoreRender to compute the radiative transfer from a realistic 3D description of the crop structure. We checked its good performances by comparison with the state of the art 3D RT models using the RAMI online model checker. Then, we designed a speed-up method to simulate canopy reflectance from a limited number of soil and leaf optical properties. Based on crop specific databases simulated from LuxCoreRender for wheat and maize and crop generic databases simulated from a 1D RT model, we trained some machine learning inversion algorithms to retrieve canopy state variables like Green Area Index GAI, Cab and Canopy Chlorophyll Content (CCC). Results on both simulations and in situ data combined with SENTINEL2 images showed that crop specific algorithms outperform the generic one for the three variables, especially when the canopy structure breaks the 1D turbid medium assumption such as in maize where rows are dominant during a significant part of the growing season
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Poitou, Damien. "Modélisation du rayonnement dans la simulation aux grandes échelles de la combustion turbulente." Thesis, Toulouse, INPT, 2009. http://www.theses.fr/2009INPT035G/document.
Full textAbstract:
La simulation de la combustion turbulente connait un nouvel essor avec l'introduction de la Simulation aux Grandes Échelles (SGE) qui permet de prédire l'évolution in stationnaire de l'écoulement réactif turbulent. Dans ce contexte la prise en compte du rayonnement soulève des questions d'ordre a la fois fondamental et pratique. En effet les processus physiques du rayonnement et de la combustion sont de nature radicalement différente : la combustion est contrôlée par des échanges locaux sur une durée finie, alors que le rayonnement est instantané et fait intervenir des échanges a distance. En premier lieu il convient de s'interroger sur l'impact de la modélisation SGE de la combustion turbulente sur le rayonnement. Cette question est traitée dans le cadre plus général de l'interaction rayonnement-turbulence. A partir d'études théoriques et numériques, il est montre que cette interaction est faible et qu'une solution SGE peut être directement utilisée pour un calcul radiatif, sans modélisation supplémentaire. Il s'agit ensuite de mettre en place de façon pratique le couplage in stationnaire rayonnement-combustion turbulente. Un point clé est la réduction du temps de calcul pour le rayonnement, et diverses stratégies sont proposées. En particulier un nouveau modèle spectral est introduit, utilisant une technique de tabulation et garantissant un niveau de précision suffisant. Le temps de calcul radiatif a ainsi été réduit de deux ordres de grandeur, permettant la réalisation d'un calcul couple sur une configuration de flamme pré-melangée turbulenteSimulation of turbulent combustion has gained high potential with the Large Eddy Simulation (LES) approach, allowing to predict unsteady turbulent reactive flows. In this context, taking into account radiation rises new fundamental and practical questions. Indeed the physics involved in radiation and in combustion are completely different : combustion is controlled by local exchanges and finite times whereas radiation is instantaneous and is based on non-local exchanges. In a first step, the impact of LES modelling of turbulent combustion on radiation is regarded. This question is treated in the more general frame of the turbulence-radiation interaction. From theoretical and numerical studies, it is shown that this interaction is weak in the LES context so that LES solutions can be directly coupled to radiative calculations, without further modelling. Then the unsteady coupling of radiation and turbulent combustion is realised. A key point is the reduction of calculation time of radiation, and several strategies are proposed. In particular a new global spectral model is introduced, using a tabulation technique and ensuring a sufficient level of accuracy. The radiative time calculation is finally decreased by two orders of magnitude, enabling the realization of a coupled calculation of a turbulent premixed flame
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Moutier, William. "Utilisation de la cytométrie en flux pour une meilleure connaissance de la diffusion individuelle des particules : Application au phytoplancton." Thesis, Littoral, 2016. http://www.theses.fr/2016DUNK0439/document.
Full textAbstract:
L'objectif était d'utiliser le cytomètre en flux (Cytosense, CytoBuoy b.v., NL) afin de comprendre l'influence des paramètres structurels et morphologiques des cellules phytoplanctoniques sur la rétrodiffusion. Nous avons analysé les propriétés optiques des cellules sur différentes phases de croissance. Une expérience en microcosme a été réalisée sur deux espèces (Thalassiosira pseudonana et Chlamydomonas Concordia) durant 20 jours. Les efficacités de diffusion avant et de côté de Thalassiosira pseudonana étaient respectivement 2,2 et 1,6 fois plus importantes que celles de Chlamydomonas Concordia. Les variations intra- et inter-espèces ont été expliquées par des simulations théoriques et des mesures in situ (biogéochimiques et observations au microscope à balayage électronique). Les mesures in situ ont permis d'obtenur des informations sur la structure des cellules (e.g. épaisseur de la frustule). L'efficacité de diffusion avant est impactée par l'agrégation et la taille des cellules. L'indice de réfraction réel du chloroplaste est un paramètre clé pouvant expliquer les variations de l'efficacité de côté. À l'avenir, nous recommandons d'utiliser un modèle à deux couches (cytoplasmes-chloroplaste) pour simuler les propriétés optiques des cellules phytoplanctoniques. Une analyse de la relation entre la concentration en carbone organique particulaire (POC) et le coefficient de rétrodiffusion a été effectuée. Des relations linéaires fortes ont été observées uniquement durant la phase exponentielle. Une reconstruction du coefficient de rétrodiffusion a permis de mettre en évidence que le POC était d'origine phytoplanctonique pour une espèce et d'origine bactérienne pour l'autreThe objective was to use the flow cytometer (Cytosense, CityBuoy B.V., NL) to understand the influence of structural and morphological parameters of phytoplankton cells on the backscattering. We have analyzed the optical properties of the cells over different growth phases. A microcosm experiment was performed on two species (Thalassiosira pseudonana and Chlamydomonas Concordia) during 20 days. The forward and sideward efficiencies of Thalassiosira pseudonana were, respectively, 2.2 and 1.6 times higher than the efficiencies Chlamydomonas Concordia. The inter- and intra-species variations were explained by theoretical simulations and in situ measurements (biogeochemical and observations from scanning electron microscope). In situ measurements were used to obtain informations about the cell structure (e.g. thickness of the frustule). The forward efficiency was impacted by the aggregation and the cell size. The real refractive index of the chloroplast is a key parameter that could explain variations of the sideward efficiency. In the future, we recommend to use a two-layered sphere model (cytoplasm-chloroplast) to simulate the optical properties of phytoplankton cells. An analysis of the relationship between the particulate organic carbon concentration (POC) and the backscattering coefficient was performed. Strong linear relationships were observed only during the exponential phase. A reconstruction of the backscattering coefficient permitted to highlight that the POC was from phytoplankton cells origin for a species and bacterial origin for the other one
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Hong, Seung-Ho. "Monte Carlo simulation of radiation heat transfer in a three-dimensional enclosure containing a circular cylinder." Thesis, 1994. http://hdl.handle.net/1957/35722.
Full text
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IMRAN, HAFIZ ALI. "Remote sensing tools for monitoring grassland plant leaf traits and biodiversity." Doctoral thesis, 2022. http://hdl.handle.net/10449/74719.
Full textAbstract:
Grasslands are one of the most important ecosystems on Earth, covering approximately onethird of the Earth’s surface. Grassland biodiversity is important as many services provided by such
ecosystems are crucial for the human economy and well-being. Given the importance of grasslands
ecosystems, in recent years research has been carried out on the potential to monitor them with
novel remote sensing techniques. Improved detectors technology and novel sensors providing finescale hyperspectral imagery have been enabling new methods to monitor plant traits (PTs) and
biodiversity.
The aims of the work were to study different approaches to monitor key grassland PTs such
as Leaf Area Index (LAI) and biodiversity-related traits. The thesis consists of 3 parts: 1)
Evaluating the performance of remote sensing methods to estimate LAI in grassland ecosystems, 2)
Estimating plant biodiversity by using the optical diversity approach in grassland ecosystems, and
3) Investigating the relationship between PTs variability with alpha and beta diversity for the
applicability of the optical diversity approach in a subalpine grassland of the Italian Alps
To evaluate the performance of remote sensing methods to estimate LAI, temporal and
spatial observations of hyperspectral reflectance and LAI were analyzed at a grassland site in Monte
Bondone, Italy (IT-MBo). In 2018, ground temporal observations of hyperspectral reflectance and
LAI were carried out at a grassland site in Neustift, Austria (AT-NEU). To estimate biodiversity, in
2018 and 2019 a floristics survey was conducted to determine species composition and
hyperspectral data were acquired at two grassland sites: IT-MBo and University of Padova’s
Experimental Farm, Legnaro, Padua, Italy (IT-PD) respectively. Furthermore, in 2018,
biochemistry analysis of the biomass samples collected from the grassland site IT-MBo was carried
out to determine the foliar biochemical PTs variability.
The results of the thesis demonstrated that the grassland spectral response across different
spectral regions (Visible: VIS, red-edge: RE, Near-infrared: NIR) showed to be both site-specific
and scale-dependent. In the first part of the thesis, the performance of spectral vegetation indices
(SVIs) based on visible, red-edge (RE), and NIR bands alongside SVIs solely based or NIRshoulder bands (wavelengths 750 - 900 nm) was evaluated. A strong correlation (R2 > 0.8) was
observed between grassland LAI and both RE and NIR-shoulder SVIs on a temporal basis, but not
on a spatial basis. Using the PROSAIL Radiative Transfer Model (RTM), it was demonstrated that
grassland structural heterogeneity strongly affects the ability to retrieve LAI, with high uncertainties
due to structural and biochemical PTs co-variation.
In the second part, the applicability of the spectral variability hypothesis (SVH) was
questioned and highlighted the challenges to use high-resolution hyperspectral images to estimate
biodiversity in complex grassland ecosystems. It was reported that the relationship between
biodiversity (Shannon, Richness, Simpson, and Evenness) and optical diversity metrics (Coefficient
of variation (CV) and Standard deviation (SD)) is not consistent across plant communities. The
results of the second part suggested that biodiversity in terms of species richness could be estimated
by optical diversity metrics with an R2 = 0.4 at the IT-PD site where the grassland plots were
artificially established and are showing a lower structure and complexity from the natural grassland
plant communities. On the other hand, in the natural ecosystems at IT-MBo, it was more difficult to
estimate biodiversity indices, probably due to structural and biochemical PTs co-variation. The
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effects of canopy non-vegetative elements (flowers and dead material), shadow pixels, and
overexposed pixels on the relationship between optical diversity metrics and biodiversity indices
were highlighted.
In the third part, we examined the relationship between PTs variability (at both local and
community scales, measured by standard deviation and by the Euclidean distances of the
biochemical and biophysical PTs respectively) and taxonomic diversity (both α-diversity and βdiversity, measured by Shannon’s index and by Jaccard dissimilarity index of the species, families,
and functional groups percent cover respectively) in Monte Bondone, Trentino province, Italy. The
results of the study showed that the PTs variability metrics at alpha scale were not correlated with
α-diversity. However, the results at the community scale (β-diversity) showed that some of the
investigated biochemical and biophysical PTs variations metrics were associated with β-diversity.
The SVH approach was also tested to estimate β-diversity and we found that spectral diversity
calculated by spectral angular mapper (SAM) showed to be a better proxy of biodiversity in the
same ecosystem where the spectral diversity failed to estimate alpha diversity, this leading to the
conclusion that the link between functional and species diversity may be an indicator of the
applicability of optical sampling methods to estimate biodiversity.
The findings of the thesis highlighted that grassland structural heterogeneity strongly affects
the ability to retrieve both LAI and biodiversity, with high uncertainties due to structural and
biochemical PTs co-variation at complex grassland ecosystems. In this context, the uncertainties of
satellite-based products (e.g., LAI) in monitoring grassland canopies characterized by either
spatially or temporally varying structure need to be carefully taken into account. The results of the
study highlighted that the poor performance of optical diversity proxies in estimating biodiversity in
structurally heterogeneous grasslands might be due to the complex relationships between functional
diversity and biodiversity, rather than the impossibility to detect functional diversity with spectral
proxies
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Long, Alex R. "The iterative thermal emission Monte Carlo method for thermal radiative transfer." Thesis, 2012. http://hdl.handle.net/1957/33215.
Full textAbstract:
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
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Gerstell, Marguerite F. "Part 1. Two radiative transfer models with terrestial applications. Part 2. Testing the porcupine plate hypothesis." Thesis, 1995. https://thesis.library.caltech.edu/5658/1/Gerstell_mf_1995.pdf.
Full textAbstract:
Paper I: Goody's convolution theorem for obtaining the cumulative k-distribution of a gas mixture requires stronger assumptions than the multiplicative property of band transmission; thus new experimental investigations of its effectiveness were undertaken. The convolution was found to be a useful speed optimization of k-distribution calculations at high pressures. For low pressures a variety of mixing methods were compared, all taking advantage of the idea that stratospheric lines are too narrow to overlap.
Appendix I discusses the context and application of k-distribution calculations.
Paper II: We used a "quasi-random" radiative transfer model to estimate stratospheric radiative perturbations produced by SO_2 gas, silicate ash, and H_2SO_4 aerosols after the 1982 El Chichon eruptions. One week after the last eruption, net radiative heating perturbations exceeding 20 K/day were modeled at altitudes near 26 km. Silicate ash heating may have been balanced by global enhancement of stratospheric meridional circulation, with upward velocities of 1 cm/s near Chichon's latitude. Radiative forcing by silicate ash and SO_2 gas should be included in more comprehensive models of plume evolution. Particle size distributions inferred from ash fallout rates could be wrong if radiative heating is neglected.
Paper III: Uncertainties in the solar spectrum can affect modeled net heating rates in the upper stratosphere by a factor of several. Variation among Antarctic surface albedo values in common use can affect modeled net heating rates in the lower stratosphere by tens of percent. Large uncertainties in polar cloud cover are less important to stratospheric heating models. I join Marcel Nicolet in urging support for a continuous solar observation program, and recommend that future intercomparisons of stratospheric radiation models prescribe a solar spectrum, to reveal other differences.
Appendix 2 gives the details of some further validation and sensitivity tests for the quasi-random model.
Paper IV: The Porcupine Plate was postulated in 1986 to explain difficulties in reconstructing anomalies 21 and 24 in the North Atlantic. Its main feature was thought to be a transpressive Eocene plate boundary along Charlie-Gibbs Fracture Zone. Eliminating data that could have been affected by subsequent movements of Greenland relative to North America leads to a picture that casts doubt on the Porcupine Plate hypothesis.
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Liu, Dawei. "Improvement and use of radiative transfer models to assess lunar space weathering and mechanisms for swirl formation." 2015. http://hdl.handle.net/1805/7393.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)This dissertation focuses on quantification of submicroscopic iron of different sizes, mineral abundance and grain size of lunar soils using Hapke's radiative transfer model. The main objective is to explore implications of these results for assessing the relative importance of solar wind implantation versus micrometeorite impacts for lunar space weathering as well as three hypotheses (solar wind deflection, comet impact and dust transport) for swirl formation on the Moon. Results from this study can help to make connections between ordinary chondritic meteorites and asteroids, and put physical and chemical constraints on heating processes in the early solar system.
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Qu, Yan. "Silicon wafer surface temperature measurement using light-pipe radiation thermometers in rapid thermal processing systems." Thesis, 2006. http://hdl.handle.net/2152/2794.
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Stone, Kenneth A. "Modeled and observed longwave radiances at the top of the atmosphere." Thesis, 1990. http://hdl.handle.net/1957/28726.
Full textAbstract:
One method of estimating the longwave radiative heating of the atmosphere is to
combine satellite observations of emitted radiances with those computed from synoptic
temperature and humidity profiles. Modeled and observed radiances are brought into
agreement by altering cloud properties or even by adjusting the temperature and water
vapor profiles.
Here this strategy is examined in an exploratory study using global meteorological
data sets and a radiative transfer model typical of those found in general circulation
models. Calculated radiances are compared to those observed by the Earth Radiation
Budget Satellite (ERBS). Input for the model is obtained from the National Meteorological
Center (NMC) in the form of vertical profiles of temperature and relative
humidity. The comparisons are limited to clear sky as deduced by ERBE algorithms,
and additional filtering which requires homogeneous surface type for a 3 x 3 array
of ERBS scanner fields of view. Observations are obtained from 60° N to 60° S that
lie within 30 minutes of the NMC analysis time. Following the work of Ramanathan
and Downey (1986), comparisons are separated into climatologically distinct groups as
well as by satellite viewing angle. This separation is an attempt to distinguish between
biases in the radiation model and those in the NMC data set. Results are presented for
the months of July 1985, and January 1986.
A comparison of the present radiation model's output with that obtained from a
Geophysical Fluid Dynamics Laboratory (GFDL) model shows a bias of nearly 3% in
the present model for a standard mid-latitude summer profile.
Global results show a negative bias in the modeled values for nearly all scenes,
except for nighttime desert. The nighttime desert bias may be a result of a skin-air
temperature difference not resolved by the NMC analyses. The overall negative bias
may be a result of an overestimation of water vapor for regions with low relative
humidity.Graduation date: 1991
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Qualey, Douglas L. "Radiation from an infinite plane to parallel rows of infinitely long tubes - hottel extended." Thesis, 1994. http://hdl.handle.net/1957/35314.
Full textAbstract:
A two-dimensional model for predicting the rate of radiation
heat transfer for the interior of an industrial furnace is described.
The model is two-dimensional due to the assumptions of the heat
source as an infinite radiating plane and the heat sink as rows of
parallel tubes that are both infinite in length and in number. A
refractory back wall, located behind the tube rows, is also included
in some of the model configurations.
The optical properties for the heat source, heat sink, and
refractory back wall are simplified by assuming the "black-body"
case: all are treated as perfect absorbers and emitters of radiation.
This assumption allows three different solution techniques-a
graphical, crossed-string, and numerical method-to be used in
solving for the radiant transfer rate. The numerical method, an
innovative Monte Carlo technique, is the one employed in this study.
Hottel used a graphical technique to solve the furnace model
for a two row configuration in which the tubes are arranged on
equilateral triangular centers. His results, along with those
produced by the crossed-string method, are used in this work to
validate the numerical technique. Having been validated, the
numerical method was then employed to extend Hottel's work by
adding more tube rows to the original equilateral triangular
configuration and by generalizing the results to isosceles
arrangements.
Findings of this investigation are summarized in a table that
lists the direct view factors for a ten tube row configuration
arranged in an equilateral triangular array. Values from this table
can be used to solve the transfer rate problem for twenty different
cases by assuming a nonconducting refractory back wall. Results for
twelve cases are represented graphically in this document The
results are used to demonstrate the importance of a refractory back
wall on overall radiation absorption. Examinations of the two row
and five row cases for an isosceles triangular array indicate that
the tabular values can be applied to any isosceles arrangement if the
ratio of row separation distance to tube center-to-center distance
is 0.7 or greater.Graduation date: 1995
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Wang, Chenxi. "Investigation of Thin Cirrus Cloud Optical and Microphysical Properties on the Basis of Satellite Observations and Fast Radiative Transfer Models." Thesis, 2013. http://hdl.handle.net/1969.1/151213.
Full textAbstract:
This dissertation focuses on the global investigation of optically thin cirrus cloud optical thickness (tau) and microphysical properties, such as, effective particle size (D_(eff)) and ice crystal habits (shapes), based on the global satellite observations and fast radiative transfer models (RTMs). In the first part, we develop two computationally efficient RTMs simulating satellite observations under cloudy-sky conditions in the visible/shortwave infrared (VIS/SWIR) and thermal inferred (IR) spectral regions, respectively. To mitigate the computational burden associated with absorption, thermal emission and multiple scattering, we generate pre-computed lookup tables (LUTs) using two rigorous models, i.e., the line-by-line radiative transfer model (LBLRTM) and the discrete ordinates radiative transfer model (DISORT).
The second part introduces two methods (i.e., VIS/SWIR- and IR-based methods) to retrieve tau and D_(eff) from satellite observations in corresponding spectral regions of the two RTMs. We discuss the advantages and weakness of the two methods by estimating the impacts from different error sources on the retrievals through sensitivity studies.
Finally, we develop a new method to infer the scattering phase functions of optically thin cirrus clouds in a water vapor absorption channel (1.38-µm). We estimate the ice crystal habits and surface structures by comparing the inferred scattering phase functions and numerically simulated phase functions calculated using idealized habits.
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Luderer, Gunnar. "Modeling and application of multispectral oceanic sun glint observations." Thesis, 2003. http://hdl.handle.net/1957/28762.
Full textAbstract:
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
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Cleveland, Mathew A. "Radiative heat transfer in combustion applications : parallel efficiencies of two gas models, turbulent radiation interactions in particulate laden flows, and coarse mesh finite difference acceleration for improved temporal accuracy." Thesis, 2011. http://hdl.handle.net/1957/26119.
Full textAbstract:
We investigate several aspects of the numerical solution of the radiative transfer
equation in the context of coal combustion: the parallel efficiency of two commonly used
opacity models, the sensitivity of turbulent radiation interaction (TRI) effects
to the presence of coal particulate, and an improvement of the order of temporal
convergence using the coarse mesh finite difference (CMFD) method.
There are four opacity models commonly employed to evaluate the radiative
transfer equation in combustion applications; line-by-line (LBL), multigroup, band,
and global. Most of these models have been rigorously evaluated for serial computations
of a spectrum of problem types [1]. Studies of these models for parallel
computations [2] are limited. We assessed the performance of the Spectral-Line-
Based weighted sum of gray gasses (SLW) model, a global method related to K-distribution
methods [1], and the LBL model. The LBL model directly interpolates
opacity information from large data tables. The LBL model outperforms the SLW
model in almost all cases, as suggested by Wang et al. [3]. The SLW model, however,
shows superior parallel scaling performance and a decreased sensitivity to
load imbalancing, suggesting that for some problems, global methods such as the
SLW model, could outperform the LBL model.
Turbulent radiation interaction (TRI) effects are associated with the differences
in the time scales of the
fluid dynamic equations and the radiative transfer equations.
Solving on the
fluid dynamic time step size produces large changes in the
radiation field over the time step. We have modifed the statistically homogeneous,
non-premixed
flame problem of Deshmukh et al. [4] to include coal-type particulate.
The addition of low mass loadings of particulate minimally impacts the TRI
effects. Observed differences in the TRI effects from variations in the packing fractions
and Stokes numbers are difficult to analyze because of the significant effect
of variations in problem initialization. The TRI effects are very sensitive to the
initialization of the turbulence in the system. The TRI parameters are somewhat
sensitive to the treatment of particulate temperature and the particulate optical
thickness, and this effect are amplified by increased particulate loading.
Monte Carlo radiative heat transfer simulations of time-dependent combustion
processes generally involve an explicit evaluation of emission source because of
the expense of the transport solver. Recently, Park et al. [5] have applied quasidiffusion with Monte Carlo in high energy density radiative transfer applications.
We employ a Crank-Nicholson temporal integration scheme in conjunction with the
coarse mesh finite difference (CMFD) method, in an effort to improve the temporal
accuracy of the Monte Carlo solver. Our results show that this CMFD-CN method
is an improvement over Monte Carlo with CMFD time-differenced via Backward
Euler, and Implicit Monte Carlo [6] (IMC). The increase in accuracy involves very
little increase in computational cost, and the figure of merit for the CMFD-CN
scheme is greater than IMC.Graduation date: 2012