One of the negative effects that a laser beam experiences as it propagates through the atmosphere is intensity fluctuations or scintillation. Because scintillation-- as it pertains to laser radar and laser satellite communication systems-- is the main subject of this research, the assumption of an optical element ( such as a Gaussian lens) along the propagation path in front of the detector is valid. The mathematical addition of optical elements to the propagation path is treated using the ABCD ray matrix method. The expression for scintillation is derived, analyzed, and numerically calculated for positions to the left and right of the image plane, which is behind the collecting lens of a receiver system. Simultaneously, the behavior of the scintillation is investigated when the aperture size of the lens is increased. The results are compared to the aperture averaging effect experienced when the beam is in the image plane. This is a per-unit scintillation decrease because the aperture averages it over the surface of the lens.

Earths and mini Neptunes likely have a wide range of atmospheric compositions, ranging from low molecular mass atmospheres of H-2 to higher molecular atmospheres of water, CO2, N-2, or other species. Here we systematically investigate the effects of atmospheric bulk compositions on temperature and wind distributions for tidally locked sub-Jupiter-sized planets, using an idealized 3D general circulation model (GCM). The bulk composition effects are characterized in the framework of two independent variables: molecular weight and molar heat capacity. The effect of molecular weight dominates. As the molecular weight increases, the atmosphere tends to have a larger day-night temperature contrast, a smaller eastward phase shift in the thermal phase curve, and a smaller zonal wind speed. The width of the equatorial super-rotating jet also becomes narrower, and the "jet core" region, where the zonal-mean jet speed maximizes, moves to a greater pressure level. The zonal-mean zonal wind is more prone to exhibit a latitudinally alternating pattern in a higher molecular weight atmosphere. We also present analytical theories that quantitatively explain the above trends and shed light on the underlying dynamical mechanisms. Those trends might be used to indirectly determine the atmospheric compositions on tidally locked sub-Jupiter-sized planets. The effects of the molar heat capacity are generally small. But if the vertical temperature profile is close to adiabatic, molar heat capacity will play a significant role in controlling the transition from a divergent flow in the upper atmosphere to a jet-dominated flow in the lower atmosphere.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1982. / Microfiche copy available in Archives and Barker. / Includes bibliographical references. / by Peter David McQuade. / M.S.

This thesis describes a method for using physically based techniques to model an explosion and the resulting side effects. Explosions are some of the most visually exciting phenomena known to humankind and have become nearly ubiquitous in action films. A realistic computer simulation of this powerful event would be cheaper, quicker, and much less complicated than safely creating the real thing. The immense energy released by a detonation creates a discontinuous localized increase in pressure and temperature. Physicists and engineers have shown that the dissipation of this concentration of energy, which creates all the visible effects, adheres closely to the compressible Navier-Stokes equation. This program models the most noticeable of these results. In order to simulate the pressure and temperature changes in the environment, a three dimensional grid is placed throughout the area around the detonation and a discretized version of the Navier-Stokes equation is applied to the resulting voxels. Objects in the scene are represented as rigid bodies that are animated by the forces created by varying pressure on their hulls. Fireballs, perhaps the most awe-inspiring side effects of an explosion, are simulated using massless particles that flow out from the center of the blast and follow the currents created by the dissipating pressure. The results can then be brought into Maya for evaluation and tweaking.

This thesis describes a method for using physically based techniques to model an explosion and the resulting side effects. Explosions are some of the most visually exciting phenomena known to humankind and have become nearly ubiquitous in action films. A realistic computer simulation of this powerful event would be cheaper, quicker, and much less complicated than safely creating the real thing. The immense energy released by a detonation creates a discontinuous localized increase in pressure and temperature. Physicists and engineers have shown that the dissipation of this concentration of energy, which creates all the visible effects, adheres closely to the compressible Navier-Stokes equation. This program models the most noticeable of these results. In order to simulate the pressure and temperature changes in the environment, a three dimensional grid is placed throughout the area around the detonation and a discretized version of the Navier-Stokes equation is applied to the resulting voxels. Objects in the scene are represented as rigid bodies that are animated by the forces created by varying pressure on their hulls. Fireballs, perhaps the most awe-inspiring side effects of an explosion, are simulated using massless particles that flow out from the center of the blast and follow the currents created by the dissipating pressure. The results can then be brought into Maya for evaluation and tweaking.

Astronomical images taken by ground-based telescopes are subject to aberrations induced by the Earth's atmosphere. Adaptive optics (AO) provides a real-time solution to compensate for aberrated wavefronts. The University of Canterbury would like to install an AO system on the 1-m McLellan telescope at Mount John University Observatory (MJUO). The research presented in this thesis is the first step towards this goal. To design an effective AO system it is important to understand the characteristics of the optical turbulence present at a site. Scintillation detection and ranging (SCIDAR) is a remote sensing method capable of measuring the refractive index structure constant, Cn2(h), and the wind velocity profile, V(h). The dominant near ground turbulence (NGT) at MJUO required the use of both pupil-plane and generalised SCIDAR. A purpose-built SCIDAR system was designed and constructed at low cost, using primarily off-the-shelf components. UC-SCIDAR saw first light at MJUO in 2003, and has since undergone several revisions. The current version employs two channels for simultaneous pupil-plane and generalised SCIDAR measurements, and is very portable. Through the use of a different mounting plate the system could be easily placed onto any telescope. Cn2(h) profiling utilised standard analysis techniques. V(h) profiling using data from a 1-m telescope is not common, and existing analysis techniques were extended to provide meaningful V(h) profiles, via the use of partial triplet analysis. Cn2(h) profiling between 2005 and 2007 indicate strong NGT and a weak turbulent layer located at 12 - 14 km above sea level, associated with the tropopause region. During calm weather conditions, an additional layer was detected at 6 - 7 km above sea level. V(h) profiles suggest that the tropopause layer velocity is nominally 12 - 30 m/s, and that NGT velocities range from 2 m/s to over 20 m/s, dependent on weather. Little seasonal variation was detected in either Cn2(h) or V(h) profiles. The average coherence length, $r_0$, was found to be 12+-5 cm and 7+-1 cm for pupil-plane and generalised measurements respectively, for a wavelength of 589 nm. The average isoplanatic angle, $\theta_0$, was 1.5+-0.5 arcseconds and 1.1+-0.4 arcseconds for pupil-plane and generalised profiles respectively. No seasonal trends could be established in the measurements for the Greenwood frequency, $f_G$, due to gaps present in the V(h) profiles obtained. A modified Hufnagel-Valley (HV) model was developed to describe the Cn2(h) profiles at MJUO. The estimated $r_0$ from the model is 6 cm for a wavelength of 589 nm, corresponding to an uncompensated angular resolution, $\theta_{res}$, of 2.5 arcseconds. $\theta_0$ is 0.9 arcseconds. A series of V(h) models were developed, based on the Greenwood wind model with an additional Gaussian peak located at low altitudes, to encompass the various V(h) profiles seen at MJUO. Using the modified HV model for Cn2(h) profiles and the suggested model for V(h) profiles in the presence of moderate ground wind speeds, $f_G$ is estimated at 79 Hz. The Tyler frequency, $f_T$, is estimated at 11 Hz. Due to financial considerations, it is suggested that the initial AO design for MJUO focuses on the correction of tip/tilt only, utilising self-guiding, as it is unlikely that any suitable guide stars would be sufficiently close to the science object. The low $f_T$ suggests that an AO system with a bandwidth in the order of 60 Hz would be adequate for tip/tilt correction.

Astronomical images taken by ground-based telescopes are subject to aberrations induced by the Earth's atmosphere. Adaptive optics (AO) provides a real-time solution to compensate for aberrated wavefronts. The University of Canterbury would like to install an AO system on the 1-m McLellan telescope at Mount John University Observatory (MJUO). The research presented in this thesis is the first step towards this goal. To design an effective AO system it is important to understand the characteristics of the optical turbulence present at a site. Scintillation detection and ranging (SCIDAR) is a remote sensing method capable of measuring the refractive index structure constant, Cn2(h), and the wind velocity profile, V(h). The dominant near ground turbulence (NGT) at MJUO required the use of both pupil-plane and generalised SCIDAR. A purpose-built SCIDAR system was designed and constructed at low cost, using primarily off-the-shelf components. UC-SCIDAR saw first light at MJUO in 2003, and has since undergone several revisions. The current version employs two channels for simultaneous pupil-plane and generalised SCIDAR measurements, and is very portable. Through the use of a different mounting plate the system could be easily placed onto any telescope. Cn2(h) profiling utilised standard analysis techniques. V(h) profiling using data from a 1-m telescope is not common, and existing analysis techniques were extended to provide meaningful V(h) profiles, via the use of partial triplet analysis. Cn2(h) profiling between 2005 and 2007 indicate strong NGT and a weak turbulent layer located at 12 - 14 km above sea level, associated with the tropopause region. During calm weather conditions, an additional layer was detected at 6 - 7 km above sea level. V(h) profiles suggest that the tropopause layer velocity is nominally 12 - 30 m/s, and that NGT velocities range from 2 m/s to over 20 m/s, dependent on weather. Little seasonal variation was detected in either Cn2(h) or V(h) profiles. The average coherence length, $r_0$, was found to be 12+-5 cm and 7+-1 cm for pupil-plane and generalised measurements respectively, for a wavelength of 589 nm. The average isoplanatic angle, $\theta_0$, was 1.5+-0.5 arcseconds and 1.1+-0.4 arcseconds for pupil-plane and generalised profiles respectively. No seasonal trends could be established in the measurements for the Greenwood frequency, $f_G$, due to gaps present in the V(h) profiles obtained. A modified Hufnagel-Valley (HV) model was developed to describe the Cn2(h) profiles at MJUO. The estimated $r_0$ from the model is 6 cm for a wavelength of 589 nm, corresponding to an uncompensated angular resolution, $\theta_{res}$, of 2.5 arcseconds. $\theta_0$ is 0.9 arcseconds. A series of V(h) models were developed, based on the Greenwood wind model with an additional Gaussian peak located at low altitudes, to encompass the various V(h) profiles seen at MJUO. Using the modified HV model for Cn2(h) profiles and the suggested model for V(h) profiles in the presence of moderate ground wind speeds, $f_G$ is estimated at 79 Hz. The Tyler frequency, $f_T$, is estimated at 11 Hz. Due to financial considerations, it is suggested that the initial AO design for MJUO focuses on the correction of tip/tilt only, utilising self-guiding, as it is unlikely that any suitable guide stars would be sufficiently close to the science object. The low $f_T$ suggests that an AO system with a bandwidth in the order of 60 Hz would be adequate for tip/tilt correction.

Thesis (Ph.D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Dr. Paul G. Steffes; Committee Member: Dr. Gregory D. Durgin; Committee Member: Dr. Robert D. Braun; Committee Member: Dr. Thomas K. Gaylord; Committee Member: Dr. Waymond R. Scott

Made available in DSpace on 2014-06-11T19:22:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-02-26Bitstream added on 2014-06-13T19:07:52Z : No. of bitstreams: 1 dalbelo_lfa_me_prud.pdf: 1258749 bytes, checksum: 413bf515eb63448ca76790ba3eb43c75 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Atualmente é cada vez mais presente na comunidade civil a utilização do Global Positioning System (GPS). Um dos métodos de posicionamento GPS de grande destaque é o Differential GPS (DGPS). Esse método utiliza dois receptores, um como base e outro como móvel. O DGPS tem como princípio básico considerar a alta correlação dos erros provocados pela ionosfera, troposfera e órbita dos satélites. No entanto, com o afastamento entre o usuário e a estação base, a eficiência do método diminui, pois a correlação dos erros é reduzida. Mas, quando se utiliza uma rede de estações de referência, pode-se ter uma melhor modelagem dos erros na área de abrangência da rede. Surge então o conceito de DGPS em Rede (DGPSR). Alguns experimentos realizados com o DGPSR em modo pós-processados apontaram acurácia da ordem de 50 cm. Portanto, nesta pesquisa foi proposta a implementação do DGPSR em tempo real. As correções DGPSR são calculadas em tempo real por meio dos dados obtidos via Internet utilizando o protocolo Ntrip (Networked Transport of RTCM via Internet Protocol). Para isso, foram introduzidas várias alterações no software BNC, software este que foi desenvolvido pelo BKG e realiza a função do NtripClient. No que concerne às estações de referência GPS, foram utilizados dados da rede GNSS do oeste do estado de São Paulo (Rede GNSS/SP). A rede está composta, até o momento, por 10 receptores de alta tecnologia que podem ser conectados diretamente a Internet. Com relação aos resultados pode-se observar que o DGPSR utilizando 4 estações de referência apresentou melhorias de até 32% em planimetria e de 28% em altimetria, quando comparados ao DGPS utilizando somente uma estação de referência. Com relação a avaliação da latência pode-se verifica que latências de até 12 segundos parecem não causar influência nos resultados. / Nowadays, the Global Positioning System (GPS) has been very used by the civil community. One of the GPS positioning methods that have been emphasized is the Differential GPS (DGPS). In this method, two receivers are used. One of them as base and the other as rover station. The DGPS has the basic concept of considering high correlation of the errors caused by ionosphere, troposphere and satellite orbits. However, with the baseline growth the method efficiency decreases, because the errors correlation is reduced. But, using a reference station network it is possible to obtain an error modeling in the area of the network, using the network DGPS concept. Some experiments accomplished with DGPSR post processed mode presented promising results. Accuracy better than 50 cm was obtained. Therefore, in this research the goal is to implement the DGPS in real time. The corrections will be computed through data received by Internet using the Ntrip (Networked Transport of RTCM via Internet Protocol). In order to accomplish that, it was implemented several modifications in the BNC software. This software was developed by BKG and make the function of a NtripClient. It will be used a GPS network that is set up in the west of São Paulo State. This network is composed by 10 receivers of high technology that can be directly connected by Internet. Regarding the results, the DGPSR using 4 reference stations showed improvements of up to 32% in planimetry and 28% in altimetry when compared to pure DGPS. Regarding the assessment of latency it was noted that latencies of up to 12 seconds seems not to cause influence the results.

The Antarctic continent has traditionally been a successful searching ground for meteoritic material due to its cold and dry climate. Meteorites, and their microscopic analogues micrometeorites, were originally sampled from Antarctic ice and snow. Recently, however, a large collection of micrometeorites was discovered in sedimentary traps and moraine deposits from the Transantarctic Mountains, where extraterrestrial dust particles have accumulated for a prolonged time span (ca. 3–4 Ma). Micrometeorites (or ‘cosmic dust’) show unique chemical and isotopic signatures, which originate from a large and diverse amount of asteroidal and cometary bodies within the Solar System. In addition, they document major events such as the origin and evolution of the Solar System, and provide insight into the source region of their precursor bodies. These sedimentary deposits consequently represent a valuable archive that documents the flux of extraterrestrial material to Earth and ancient meteoritic events over Antarctica.Yet, much of this information is lost during the atmospheric entry stage, where cosmic dust is subjected to frictional heating and is partially or completely molten down. This may significantly alter the original physicochemical and isotopic properties of extraterrestrial dust particles. A thorough understanding of these physicochemical processes is thus required to reconstruct the atmospheric entry of cosmic dust (but also larger objects) and interpret their chemical and isotopic data. During the course of this PhD research, multiple sedimentary deposits from the Sør Rondane Mountains (Dronning Maud Land, East Antarctica) were petrographically examined and chemically-isotopically characterized using state-of-the-art instruments. Furthermore, various experiments and numerical models were constructed to replicate the atmospheric entry stage of both small- and large-sized meteoritic material. This study has demonstrated that the Sør Rondane Mountains sedimentary deposits contain a rich and pristine variety of extraterrestrial- and impact-related materials, including micrometeorites, microtektites and meteoritic condensation spherules. Statistical analysis suggests that the Sør Rondane Mountains micrometeorite collection is representative of the contemporary flux of cosmic dust to Earth. Extraterrestrial material is subjected to a complex interplay of redox and volatilization processes during atmospheric entry heating, which allow to explain the chemical trends observed in cosmic dust. Isotopic studies also suggest that at least a minor fraction of the micrometeorite population has sampled new, unknown types of asteroidal and/or cometary bodies. Microtektites and meteoritic condensation spherules have been linked to major meteoritic events on Earth ca. 790 ka and ca. 430 ka ago, respectively, and underline the importance of the Earth’s atmosphere during their formation. The results of this PhD research emphasize the scientific value of Antarctic sedimentary deposits and provide more insight into the processes taking place during the atmospheric entry of extraterrestrial material. / Le continent antarctique a traditionnellement été un terrain de recherche fructueux pour le matériel extraterrestre en raison de son climat froid et sec. Les météorites et leurs analogues microscopiques, les micrométéorites, ont été à l'origine échantillonnés dans la glace et la neige de l'Antarctique. Plus récemment, une grande collection de micrométéorites a été découverte dans des pièges sédimentaires et des dépôts de moraine des montagnes transantarctiques, où des particules de poussière extraterrestres se sont accumulées pendant une période prolongée (environ 3-4 Ma). Les micrométéorites (ou « poussière cosmique ») présentent des signatures chimiques et isotopiques uniques, qui proviennent d'une quantité importante et diversifiée de corps astéroïdes et cométaires au sein du système solaire. En outre, elles documentent des événements majeurs tels que l'origine et l'évolution du système solaire et donnent un aperçu de la région source de leurs corps parents. Ces dépôts sédimentaires représentent par conséquent une archive précieuse qui documente le flux de matière extraterrestre vers la Terre et les événements météoritiques anciens au-dessus de l'Antarctique.Pourtant, une grande partie de cette information est perdue au cours de l'étape d'entrée dans l'atmosphère, où la poussière cosmique est soumise à un chauffage par friction et est partiellement ou complètement fondue. Cela peut altérer considérablement les propriétés physico-chimiques et isotopiques d'origine des particules de poussière extraterrestres. Une compréhension approfondie de ces processus physico-chimiques est donc nécessaire pour reconstituer l'entrée atmosphérique des poussières cosmiques (mais aussi des objets plus gros) et interpréter leurs données chimiques et isotopiques. Au cours de cette recherche de doctorat, plusieurs dépôts sédimentaires des montagnes Sør Rondane (Dronning Maud Land, Antarctique de l'Est) ont été examinés pétrographiquement et caractérisés chimiquement et isotopiquement. En outre, diverses expériences et modèles numériques ont été construits pour reproduire l'étape d'entrée dans l'atmosphère de matériaux météoritiques de petite et de grande taille.Cette étude a démontré que les dépôts sédimentaires des montagnes Sør Rondane contiennent une variété riche et peu altérée de matériaux extraterrestres et de cratères d’impacts, notamment des micrométéorites, des microtektites et des sphérules de condensation météoritique. L'analyse statistique suggère que la collection de micrométéorites des montagnes Sør Rondane est représentative du flux contemporain de poussière cosmique vers la Terre. La matière extraterrestre est soumise à une interaction complexe de processus d'oxydo-réduction et de volatilisation lors de l'entrée dans l'atmosphère, ce qui permet d'expliquer les tendances chimiques observées dans la poussière cosmique. Des études isotopiques suggèrent également qu'au moins une fraction mineure de la population de micrométéorites a échantillonné de nouveaux types inconnus d’astéroïdes et/ou de comètes. Les microtektites et les sphérules de condensation météoritiques ont été liées à des événements météoritiques majeurs sur Terre il y a ~790 ka et ~430 ka, respectivement, et soulignent l'importance de l'atmosphère terrestre lors de leur formation. Les résultats de cette recherche doctorale soulignent la valeur scientifique des dépôts sédimentaires de l'Antarctique et donnent un meilleur aperçu des processus qui se déroulent lors de l'entrée dans l'atmosphère de matière extraterrestre / Doctorat en Sciences / info:eu-repo/semantics/nonPublished