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Investigation of phononic crystals for dispersive surface acoustic wave ozone sensorsWestafer, Ryan S. 01 July 2011 (has links)
The object of this research was to investigate dispersion in surface phononic crystals (PnCs) for application to a newly developed passive surface acoustic wave (SAW) ozone sensor. Frequency band gaps and slow sound already have been reported for PnC lattice structures. Such engineered structures are often advertised to reduce loss, increase sensitivity, and reduce device size. However, these advances have not yet been realized in the context of surface acoustic wave sensors. In early work, we computed SAW dispersion in patterned surface structures and we confirmed that our finite element computations of SAW dispersion in thin films and in one dimensional surface PnC structures agree with experimental results obtained by laser probe techniques. We analyzed the computations to guide device design in terms of sensitivity and joint spectral operating point. Next we conducted simulations and experiments to determine sensitivity and limit of detection for more conventional dispersive SAW devices and PnC sensors. Finally, we conducted extensive ozone detection trials on passive reflection mode SAW devices, using distinct components of the time dispersed response to compensate for the effect of temperature. The experimental work revealed that the devices may be used for dosimetry applications over periods of several days.
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Flux associations and their relationship to the underlying heterogeneous surface characteristicsBrown Mitic, Constance Maria. January 1999 (has links)
This thesis consists of analysis of three different data sets: (i) Aircraft-based eddy correlation data collected above irrigated and non-irrigated agricultural land in Southern California during the California Ozone Deposition Experiment (CODE) summer 1991; (ii) micrometeorological tower data, collected over grape and cotton canopies as part of CODE; (iii) aircraft-based eddy correlation flux data above two grid sites in the Canadian boreal forest during the Boreal Ecosystem-Atmosphere Study (BOREAS), spring and summer of 1994 and 1996. / Results from the CODE aircraft data document composition and size of the dominant structures, which transport heat and gases (H2O, CO 2 and ozone) over water stressed and non-water stressed surfaces, and the relative frequency with which structures carrying only a single scalar, or given combinations of scalars, were encountered along the flight paths. Interpretation of results provides further evidence for the existence of a second (nonphysiological) sink for ozone. The relative preponderance of structures that carry moisture, carbon dioxide and ozone simultaneously, particularly in the gradient-up mode, reflects the importance of vegetation as co-located source/sink for these scalars. The detrending procedures described in this study may help to define a more effective separation between local and mesoscale events in biosphere-atmosphere interaction. / Results from the CODE tower data indicates a single vegetated ozone sink for the grape site, but a vegetated as well as a non-vegetated sink for the cotton site. For both sites, structures simultaneously transporting significant flux contributions of CO2, H2O, heat and ozone dominate during unstable conditions. During stable conditions, unmixed single flux structures dominated over cotton but not over grape. The results of this study contribute empirical evidence about the relationship between ozone uptake and the physical and physiological state of vegetation, as well as the limitations placed on eddy scales in simulation models. / Results from the BOREAS aircraft data shows a decoupling between the surface and the atmosphere, where the patterns of vegetation, greenness and surface temperature may be quite dissimilar to those of the fluxes of sensible heat, latent heat and---to a lesser degree---CO2. Reasons for this lie in the extraordinary boundary layer conditions, high vapour pressure deficit, moist soil and hot canopies, and the response of the vegetation to these conditions. Analysis of the coherent structure compositions to some extent permits the characterization of the different sources and sinks. Overall, this study shows the importance of understanding the various interacting components of soil, vegetation and atmosphere when attempting to design process-based models for predictions in 'micrometeorologiacally' complex ecosystems.
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Nature and characteristics of tropospheric ozone over Johannesburg.Raghunandan, Atham. January 2002 (has links)
The aim of this thesis is to examine the nature and characteristics of tropospheric ozone
over Johannesburg, South Africa. Ozone, water vapour and meteorological profile data,
which form part of the MOZAIC (Measurement of Ozone and Water Vapor by Airbus In-Service
Aircraft) database for the period 1995 to 2000 were utilized in this study.
The thesis is divided into two main parts. The first part deals with the computation of total
tropospheric ozone. A clear seasonal cycle, with ozone peaking in September and October
is found. It is suggested that the main reason for the spring maximum is biomass burning,
combined with prevailing anticyclonic circulation patterns, which facilitate the build-up of
ozone over the region. Variability in TTO is greatest in January, September and November
and least during autumn and winter (April to July). The lower day-to-day variability in
autumn and winter is a reflection of the more settled weather at this time. Interannual
variability is least in January and April to June. The autumn and winter ozone values are
more consistent and appear to represent background tropospheric ozone loadings on which
the dynamic and photochemical influences of other months are superimposed.
High TTO events (>30 DU) occurred predominantly during September and October.
Enhancements in the lower troposphere occurred mostly in September and seldom lasted
for more than 1-2 consecutive days. It is suggested that these events are most likely due to
effects of local surface pollution sources, either localised biomass burning or urban-industrial
effects. An extended period of enhancement in the 7-12 km layer occurred from
14-17 September 1998 and again on 20 September 1998. The extended duration of this
event suggests that it is due to an STE event. Confirmation of this was given in a case
study of a particular MOZAIC flight on 16 September 1998 from Johannesburg to Cape
Town.
The second part of the thesis deals with the classification of ozone profiles and is used to
find pattern and order within the profiles. TWINSPAN (Two-Way INdicator SPecies
ANalysis), a cluster analysis technique, was used to classify the profiles according to the
magnitude and altitude of ozone concentration. Six distinct groups of profiles have been
identified and their characteristics described.
The HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) trajectory model
was used to relate the profiles to the origin of air masses, revealing clearly defined source
regions. The mid-tropospheric peak in summer and the low to mid-tropospheric
enhancement in spring is attributed to continental areas over central Africa and long-range
transport while local sources are responsible for the winter low tropospheric enhancement.
Reduced ozone values are due to westerlies bringing in clean maritime air.
The classification has highlighted three important findings. Firstly, it has emphasized the
pronounced seasonality of ozone profiles. It is evident that seasons are dominated by
particular patterns and by inference, the processes and transport patterns that shape
individual profiles are seasonally dependent. Secondly, the widely recognized spring
maximum in tropospheric ozone has been confirmed in this classification, but a new and
equally high summer mid-tropospheric enhancement due to the penetration of tropical air
masses from continental regions in central Africa has been identified. Thirdly, it is
suggested that the computation of a mean profile and furthermore, extrapolation of trends
based on a mean profile is meaningless, particularly for a location on the boundaries of
zonally defined meteorological regimes. / Thesis (M.A.)-University of Natal, Durban, 2002.
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Time series analysis of ozone dataGuthrey, Delparde Raleigh 01 January 1998 (has links)
No description available.
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Télédétection spatiale ultraviolette et visible de l'ozone et du dioxyde d'azote dans l'atmosphère globaleLambert, Jean-Christopher 21 April 2006 (has links)
Propulsé sur une orbite polaire en avril 1995 par l’Agence Spatiale Européenne, l’instrument Global Ozone Monitoring Experiment (GOME) est le précurseur d’une nouvelle génération de satellites dédiés à la mesure globale de la composition atmosphérique. Ce spectromètre hyperspectral mesure, entre 240 et 790 nm, à la résolution de 0,2-0,4 nm, la radiance diffusée par l’atmosphère et réfléchie par la surface terrestre et les nuages au nadir du satellite. La technique de spectroscopie d’absorption optique différentielle (DOAS) permet d’en inverser la concentration columnaire de l’ozone et du dioxyde d’azote atmosphériques.<p><p>Les travaux décrits dans cette thèse portent d’une part sur la caractérisation du contenu en information géophysique accessible par ce type de sondage atmosphérique, et d’autre part sur la mise au point des méthodes et algorithmes d’inversion propres à la mission GOME. <p><p>Au cours des premiers chapitres, nous établissons les propriétés pluridimensionnelles de lissage et d’échantillonnage du champ atmosphérique associées à l’observation du rayonnement diffusé. Nous explorons ensuite les problèmes posés par le cycle diurne des oxydes d’azote, ainsi que l’effet des gradients atmosphériques interférant avec le chemin optique. Nous analysons enfin les capacités des réseaux de télédétection de l’Organisation Mondiale Météorologique (OMM) pour le diagnostic des algorithmes et données des systèmes satellitaires.<p><p>Deux chapitres sont ensuite consacrés à la mise au point des méthodes et algorithmes d’inversion DOAS pour le processeur GDP, qui traite de manière opérationnelle les données radiométriques acquises par GOME. Nous abordons successivement le problème de la dépendance en température des sections efficaces d’absorption, l’évaluation du facteur d’amplification géométrique du chemin optique, l’estimation de la colonne fantôme masquée par les nuages, les effets de l’anomalie magnétique sud-atlantique des ceintures de radiation, et l’incidence du dioxyde d’azote troposphérique. Suit un diagnostic systématique de la mise au point du processeur GDP sur base des données globales fournies par les réseaux de l’OMM, ainsi qu’une critique comparée des algorithmes TOMS de la NASA.<p><p>Le dernier chapitre décrit la construction de la première climatologie globale du dioxyde d’azote stratosphérique et de ses variations harmoniques. Développée pour nos études du facteur d’amplification géométrique, cette climatologie composite est issue de l’analyse conjointe des jeux de données complémentaires acquis par différents satellites, par des réseaux au sol et par des ballons stratosphériques.<p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished
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