Texte remanié de: Diss. Ph.--School of archeology and oriental studies--University of Liverpool, 1995. / Bibliogr. p. 125-137. Index.

Texte remanié de: Thèse de doctorat--Histoire et philologie orientales--Liège--Faculté de philosophie et lettres, 1990. / Index. Bibliogr. p. 319-330. CIPL = Centre informatique de philosophie et lettres.

The Optical Spectrograph and InfraRed Imaging System (OSIRIS) satellite instrument spearheaded by a team of researchers at the University of Saskatchewan has provided scientists with 13 years of information about the state of the atmosphere. The success of the mission has motivated further development of the technology in a next generation instrument called the Canadian Atmospheric Tomography System (CATS) to provide better spatial and spectral resolution through a successive satellite mission. This work details the development of a proof-of-concept prototype built to test the validity of the CATS optical design. This thesis project utilized the developmental model built for the OSIRIS mission. The major modification made to the instrument replaced the optical element that defines the instrument’s field of view. This new development transformed the original single line of sight utilized by the satellite based OSIRIS instrument into three separate fields of view, which increased the imaging capabilities of the instrument. The new system has improved spatial resolution by collecting spectral information from three separate regions in the atmosphere in a single exposure, as opposed to the single region imaged by the original system. The newly developed prototype was tested on the platform of a stratospheric balloon. This test platform offered the capabilities to make limb scattered measurements similar to those that are made by a satellite based instrument. However, from the balloon geometry, the instrument required an additional pointing system to redirect the line of sight over stratospheric tangent altitudes. The design and test of this pointing system is also detailed in this work.

The development of remote sensing satellite-borne instrumentation for the study of the Earth’s atmosphere has provided an immense increase in our understanding of atmospheric trends and processes. The Canadian built OSIRIS satellite instrument uses the limb scatter technique to measure scattered sunlight for the retrieval of vertical profiles of atmospheric species such as ozone. Recently, the next generation instrument, CATS, based on the OSIRIS design, is under development to continue OSIRIS measurements into the future. One key optical design change for CATS is the ability to measure simultaneously over multiple fields of view. However, this new optical design concept needs to be tested and evaluated. To achieve this, a prototype slit plate was installed into the preflight developmental version of OSIRIS, called OSIRIS-DM, for testing in the laboratory and on a stratospheric balloon. In this thesis work, an evaluation of the performance of this multi-slit instrument was undertaken through laboratory calibrations and limb scatter measurement collection. The calibration process includes a wavelength registration, a spectral point spread function analysis, a relative calibration and an absolute calibration, all performed with laboratory equipment. Along with laboratory calibrations, this thesis work involved preparation for the stratospheric balloon mission including the development of a flight ready electronic control and communication system to operate OSIRIS-DM during the mission. The upgraded instrument was launched on September 19, 2014, and ascended to a stable float altitude of 36.5 km. The collected flight measurements were used to evaluate the calibrations and general instrument performance. Overall, the laboratory calibrations proved to be sufficiently accurate and the measurement collection produced multiple spectra that may be used for atmospheric analysis in the future. These results show that the multi-slit design of the slit plate produces an instrument that can be reliably calibrated and implemented for limb scatter measurement collection.

Au-delà de Neptune, les petits corps du système solaire se trouvent dans un environnement préservant le matériel primordial dont ils sont formés. Aussi, la caractérisation de la structure, l'aspect et la composition d'objets tels que les comètes révèle des informations vitales sur les processus de formation et évolutions qu'ils ont subis. Les petits corps du système solaire externe n'ont connus qu'un léger retraitement thermique et collisionnel, préservant ainsi des indices vitaux de l'histoire du système solaire primitif et permettant de contraindre ses propriétés. En conséquence, l'objectif de la mission ROSETTA de l'ESA était d'effectuer la première étude approfondie d'une comète (67P/Churyumov-Gerasimenko), en la suivant, l'observant et mesurant l'évolution de son activité sur les trois quarts de son orbite. La mission constituait la pierre d'angle de l'étude des petits corps du système solaire de l'ESA.L'objectif de cette thèse fut de déterminer les propriétés photométriques et spectrales, dans le visible, de la surface de la comète en utilisant les images de l'instrument OSIRIS. À cet effet, j'ai développé uneapproche pour préparer et analyser les données OSIRIS: j'ai utilisé etdéveloppé des méthodes existantes pour projeter les images calibrées surdes modèles 3D de la comète, j'ai crée et utilisé des codes pour calculerles géométries d'observations et simulé les images à partir d'éphémérides de la comète et de Rosetta, j'ai implémenté des modèles photométrique afin de déterminer les paramètres donnant le meilleur ajustement aux données. À l'aide de ces outils, j'ai analysé des jeux d'images d'OSIRIS lors de trois manoeuvres de survols effectuées en Août 2014, Février 2015 et en Avril 2016. Durant ces trois manoeuvres, la surface fut cartographiée avec une résolution métrique et centrimétrique, ainsi que sous de nombreuses angles de vue. J'ai aussi analysé des images prises au cours de la mission afin d'étudier certaines particularités de la surface et d'observer leur évolution temporelle. L'ajustement des jeux de données avec le modèle photométrique de Hapke indique que le noyau a une surface très sombre (un albédo de 4.2% à 650 nm), qu'elle diffuse la lumière plus vers la source plus que l'observateur, qu'elle est extrêmement poreuse (à plus de 80%), et que sa réflectivité augmente légèrementde manière non-linéaire, de manière explicable par la disparition des ombres. Outre la nature bi-lobale du noyau cométaire, les analyses de ces images ont montrée la présence d'hétérogénéités de morphologie, de couleurs et d'albédo sur des échelles hectométrique et décimétrique, confirmant ainsiles tendances globales mesurées par ROSETTA/OSIRIS et PHILAE/CIVA. Entre250 nm et 1000 nm, le spectre du noyau ne présente pas de signatures spectrale. La pente du spectre en fonction de la longueur d'onde est strictement positive comme pour certains Centaures et des astéroïdes de type D. Trois types de surface ont été identifiés à l'aide de la pente spectrale. Les terrains et particularités avec les pentes les plus grandes semblent poussiéreuses et desséchées, alors que ceux avec les pentes les plus faibles sont associées avec la présence de matériel riche en glace d'eau. Les images OSIRIS ont également permis de mesurer pour la première fois le rougissement de phase d'un noyau cométaire: la variation de la pente spectral avec la géométrie d'observation. Les deux années de données ont également permis de déterminer que le rougissement de phase varie avec la distance héliocentrique, atteignant sa valeur la plus faible quand la comète est proche du périhélie. Tout comme l'observation de variations diurnes et de falaises fraîchement fracturées, ce résultat indique que sous la surface du noyau, se trouve du matériel riche en glace d'eau. / Small bodies of the outer solar system, beyond Neptune, are in an environment that can preserve the base material from which they are formed. Hence the determination of the structure, aspect, and composition of objects such as comets yield vital informations about the formation and evolution processes they went through. Small bodies from the outer solar system have undergone weak thermal and collisionnal reprocessing, thus preserving vital clues on the history of the early solar system, which can constrain its properties. Hence the objective of the European Space Agency/ROSETTA mission was to perform the first in-depth study of a comet (67P/Churyumov-Gerasimenko), following it inbound to and outbound from perihelion, observing it and monitoring the evolution of its activity during most of its orbit. This mission constituted the cornerstone of the study of small bodies of the solar system by ESA.The aim of this thesis has been to determine the photometric characteristics and the spectral properties, from the near-ultraviolet to the near-infrared, of the comet' surface using the images taken by the OSIRIS instrument. For this purpose, I developped an approach to prepare and analyse OSIRIS' datasets: I used and build on existing methods to register calibrated images to a 3D model of the comet, I created and used codes to compute the observational geometries and simulate OSIRIS images using the comet's and Rosetta's ephemerids, I implemented photometric models to determine the parameters required to fit the datasets.Using those tools, I analysed sets of images acquired by OSIRIS during three flyby maneuvers executed in August 2014, in February 2015 and in April 2016. On those three events, the surface was mapped at a meter and sub-meter resolution and also under multiple observing conditions. I also further analysed images taken throughout the mission to investigate particular surface features and signs of temporal evolution. In the description of the Hapke photometric model, the fitting of those dataset point to a nucleus with a very dark surface (4.2% albedo at 650 nm), scattering more light towards the source than the observer, with a high upper-surface porosity (over than 80%), and displaying a limited non-linear increase in reflectivity when source and observer are aligned over the comet' surface, most probably associated with the shadow-hiding phenomemon. Beyond the obvious bilobate nature of the cometary nucleus, the analyses of those images have shown that it present heterogeneities in morphology, colours and albedo of the comet' surface from the hundred of meters to the decimeter scale, confirming the trend noticed from other ROSETTA/OSIRIS and PHILAE/CIVA observations. In the wavelength domain between 250 nm and 1000 nm, the spectrum of the nucleus does not present any band features. The slope of the spectrum increases monotonously with the wavelength in a similar way to certain Centaurs and D-type asteroids. Three categories of surface were identified based on this spectral slope. Terrains and features with the largest slopes appear dusty and dessicated while those with small or flat slopes have associated with the presence of water-ice-rich material. The OSIRIS images have also allowed to measure for the first time the phase reddening effect on a cometary nucleus, that is the variation of the spectral slope with the viewing geometry. The two years of monitoring have also allowed to further determine that the phase reddening of the nucleus varies with the heliocentric distance, reaching its lowest value while the comet was close to perihelion. This result along with observations of diurnal colour variations and of freshly fractured cliffs point to the presence of a higher proportion of water-ice material at a mere distance under the nucleus surface.

Clouds have pivotal influence on the Earth's hydrological cycle and climate system because they are intricately involved in the dynamical, chemical, and radiative processes within the upper troposphere and lower stratosphere. Cirrus clouds occur at high altitude around the tropopause level and, despite their thin appearance and low optical thickness, they contribute to the radiative balance of the atmosphere. The processes in this region of the atmosphere have become increasingly important for a clear understanding of feedback mechanisms in the climate system. The Canadian designed and built Optical Spectrograph and Infrared Imaging System (OSIRIS) satellite instrument measures the spectrum of sunlight scattered from the Earth's atmosphere at wavelengths from the ultraviolet (280 nm) to the near infrared (810 nm). The limb scattering measurement technique allows OSIRIS to collect information on the vertical profile of atmospheric chemical and particle composition at a resolution of approximately 2km with nearly global daily coverage. In this work, a technique characterizing the distribution of cirrus cloud top occurrences from OSIRIS limb scattering radiance profiles is presented. The technique involves computing residual profiles by comparing normalized measured radiance and modelled molecular density profiles where mismatches between the two traces indicate the presence of clouds. Probability density functions of scattering residuals show the distribution is not a continuum measurement; there is a clear distinction between the cloudy and cloud-free conditions. Observations show high cloud top occurrences in the upper troposphere and lower stratosphere region above Indonesia and Central America. Results obtained using the high altitude cloud detection technique and OSIRIS measurements are compared to those by Sassen et al. (2008) who used CALIPSO nadir measurements and to those by Wang et al. (1996) who used SAGE II solar occultation measurements of cirrus clouds. The cloud detection technique is applied to three case studies. Cloud top detections are used to support results presented in Dessler (2009) who theorized the local relative humidity controls either dehydration or hydration of the lower stratosphere through the efficiency of evaporation of ice lofted by deep convection. The second study makes use of the cloud detection technique to eliminate cloud-containing scans as to identify an Asian Tropopause Aerosol Layer in support of Vernier et al. (2011). Finally, the technique is used to track the dispersion and evolution of the volcanic plume following the Sarychev eruption in June 2009 since monitoring volcanic plumes is an effective way to help mitigate aviation hazards.

OSIRIS, a Canadian built instrument on-board the Swedish-led remote sensing satellite, Odin, consists in part of three single lens imagers that measure near infrared light from atmospheric scattering and emission. A full calibration of the imaging system is required to remove all instrument dependent effects that modify the observations. <p>This work presents the characterization and calibration of the OSIRIS imaging system in an attempt to produce observations that are instrument independent measurements of the atmospheric brightness. The required product is the number of photons per second emitted, or scattered, from the atmosphere that are within the sampling wavelength range and incident on the detector area in the instrument field of view. <p>A major portion of the present work involves understanding the dark current production mechanisms and the development of a technique to characterize the dark current and manufacturer imposed electronic offsets. It is demonstrated that with a current set of dark calibration images, the developed algorithm effectively removes the dark current and electronic offsets over a wide operating temperature range. The relative calibration of pixels is presented in terms of the electronic gain, or flat field response, and the angular look direction. It is apparent that a change in the relative pixel gain occurred between pre-flight calibration and the first in-flight images. However, it is shown that with a recalculation of the flat field response using in-flight images, an acceptable gain calibration is obtained. The angular look direction of the pixels is determined from the results of two separate in-flight experiments. The characterization and removal of the stray light signal is shown to be effective. <p>Finally, the absolute calibration of the instrument is presented. While several issues remain to be addressed, the comparison with a simple atmospheric brightness model provides a first order verification of the results.

OSIRIS, a Canadian built instrument on-board the Swedish-led remote sensing satellite, Odin, consists in part of three single lens imagers that measure near infrared light from atmospheric scattering and emission. A full calibration of the imaging system is required to remove all instrument dependent effects that modify the observations. <p>This work presents the characterization and calibration of the OSIRIS imaging system in an attempt to produce observations that are instrument independent measurements of the atmospheric brightness. The required product is the number of photons per second emitted, or scattered, from the atmosphere that are within the sampling wavelength range and incident on the detector area in the instrument field of view. <p>A major portion of the present work involves understanding the dark current production mechanisms and the development of a technique to characterize the dark current and manufacturer imposed electronic offsets. It is demonstrated that with a current set of dark calibration images, the developed algorithm effectively removes the dark current and electronic offsets over a wide operating temperature range. The relative calibration of pixels is presented in terms of the electronic gain, or flat field response, and the angular look direction. It is apparent that a change in the relative pixel gain occurred between pre-flight calibration and the first in-flight images. However, it is shown that with a recalculation of the flat field response using in-flight images, an acceptable gain calibration is obtained. The angular look direction of the pixels is determined from the results of two separate in-flight experiments. The characterization and removal of the stray light signal is shown to be effective. <p>Finally, the absolute calibration of the instrument is presented. While several issues remain to be addressed, the comparison with a simple atmospheric brightness model provides a first order verification of the results.

The advent of satellite limb scatter measurements has allowed the stratosphere to be studied at a scope unparalleled by previous observational techniques, affording the opportunity to study structures on both small spacial and temporal scales. Utilizing these measurements to their fullest has fueled the development of radiative transfer models to simulate the measurements, but also inversion techniques to retrieve atmospheric parameters. The limb scatter instrument OSIRIS, onboard the Odin satellite, is currently used in conjunction with the SASKTRAN radiative transfer model and multiplicative algebraic reconstruction technique to retrieve stratospheric aerosol extinction. In this work, the aerosol information content of limb scatter measurements is explored and an improved version of the aerosol retrieval is developed through the simultaneous retrieval of a second aerosol parameter, the Angstrom coefficient, which is related to particle size. The sensitivity of limb scatter measurements to aerosol is investigated through forward modelling of OSIRIS measurements as a function of wavelength, satellite geometry and particle size. Information content of the measurements is investigated to determine the feasibility of retrieving various aerosol size parameters and a simple linear inversion technique is tested. Results from this study are used to develop a non-linear inversion technique with minimal sensitivity to the required assumptions. Incorporation of longer wavelength data into the retrieval allows for the determination of the wavelength dependence of the scattered signal, which when combined with a lognormal particle size distribution of constant mode width allows for the retrieval of aerosol number density and mode radius. Conversion of these parameters to extinction and the Angstrom coefficient provides retrieved quantities with minimal dependence on the assumed size distribution. Application of this technique to the OSIRIS data set shows improved extinction results through both internal comparisons of the data and when compared with other results from SAGE II, III and CALIPSO satellite measurements. Although the retrieved Angstrom coefficient shows some bias due to the required assumptions, comparisons with the SAGE II data set show considerable improvement over the apriori estimate.

Osnabrück, Univ., Diss., 2001. / Computerdatei im Fernzugriff.