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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

Atmospheric Sounding Data as Tools for Forecasting Severe Hail and Ozone Accumulation in Arizona during the North American Monsoon

January 2019 (has links)
abstract: Monsoon hazards routinely affect the community, economy, and environment of the American Southwest. A common link for hazard development during the North American Monsoon concerns the interplay between temperature, moisture, and wind in the vertical atmosphere controlled by an unstable monsoon circulation. This dissertation investigates vertical atmospheric patterns using in-situ sounding data, specifically, 1) environments favorable for severe hail on the Colorado Plateau, 2) significant parameters distinguishing unhealthy versus healthy ozone days in Phoenix, Arizona, and 3) vertical profile alignments associated with distinct ranges in ozone concentrations observed in Phoenix having defined health impacts. The first study (published in the Journal of the Arizona-Nevada Academy of Science) determines significant variables on Flagstaff, Arizona 12Z rawinsonde data (1996-2009) found on severe hail days on the Colorado Plateau. Severe hail is related to greater sub-300 hectopascals (hPa) moisture, a warmer atmospheric column, lighter above surface wind speeds, more southerly to southeasterly oriented winds throughout the vertical (except at the 700 hPa pressure level), and higher geopotential heights. The second study (published in Atmospheric Environment) employs principal component, linear discriminant, and synoptic composite analyses using Phoenix, Arizona rawinsonde data (2006-2016) to identify common monsoon patterns affecting ozone accumulation in the Phoenix metropolitan area. Unhealthy ozone occurs with amplified high-pressure ridging over the Four Corners region, 500 hPa heights often exceeding 5910 meters, surface afternoon temperatures typically over 40°C, lighter wind speeds in the planetary boundary layer under four ms-1, and persistent light easterly flow between 700-500 hPa countering the daytime mountain-valley circulation. The final study (under revision in Weather and Forecasting) assesses composite atmospheric sounding analysis to forecast Air Quality Index ozone classifications of Good, Moderate, and collectively categories exceeding the U.S. EPA 2015 standard. The analysis, using Phoenix 12Z rawinsonde data (2006-2017), identifies the existence of “pollutant dispersion windows” for ozone accumulation and dispersal in Phoenix. Ultimately, monsoon hazards result from a complex and evolving vertical atmosphere. This dissertation demonstrates the viability using available in-situ vertical upper-air data to anticipate recurring atmospheric states contributing to specific hazards. These results will improve monsoon hazard prediction in an effort to protect public and infrastructure. / Dissertation/Thesis / Doctoral Dissertation Geography 2019
52

The Development of Unique Focal Planes for High-Resolution Suborbital and Ground-Based Exploration

January 2019 (has links)
abstract: The development of new Ultra-Violet/Visible/IR range (UV/Vis/IR) astronomical instrumentation that use novel approaches for imaging and increase the accessibility of observing time for more research groups is essential for rapid innovation within the community. Unique focal planes that are rapid-prototyped, low cost, and provide high resolution are key. In this dissertation the emergent designs of three unique focal planes are discussed. These focal planes were each designed for a different astronomical platform: suborbital balloon, suborbital rocket, and ground-based observatory. The balloon-based payload is a hexapod-actuated focal plane that uses tip-tilt motion to increase angular resolution through the removal of jitter – known as the HExapod Resolution-Enhancement SYstem (HERESY), the suborbital rocket imaging payload is a Jet Propulsion Laboratory (JPL) delta-doped charge-coupled device (CCD) packaged to survive the rigors of launch and image far-ultra-violet (FUV) spectra, and the ground-based observatory payload is a star centroid tracking modification to the balloon version of HERESY for the tip-tilt correction of atmospheric turbulence. The design, construction, verification, and validation of each focal plane payload is discussed in detail. For HERESY’s balloon implementation, pointing error data from the Stratospheric Terahertz Observatory (STO) Antarctic balloon mission was used to form an experimental lab test setup to demonstrate the hexapod can eliminate jitter in flight-like conditions. For the suborbital rocket focal plane, a harsh set of unit-level tests to ensure the payload could survive launch and space conditions, as well as the characterization and optimization of the JPL detector, are detailed. Finally, a modification of co-mounting a fast-read detector to the HERESY focal plane, for use on ground-based observatories, intended to reduce atmospherically induced tip-tilt error through the centroid tracking of bright natural guidestars, is described. / Dissertation/Thesis / Doctoral Dissertation Exploration Systems Design 2019
53

Observations of water vapour in the middle atmosphere

Lossow, Stefan January 2008 (has links)
<p>Water vapour is the most important greenhouse gas and plays a fundamental role in the climate system and for the chemistry of the Earth's atmosphere. This thesis presents observations of water vapour in the middle atmosphere with a particular focus on the mesosphere. The majority of these observations presented in this thesis have been performed by the Swedish satellite Odin, providing global observations since 2001. Further observations come from the Hygrosonde-2 campaign in December 2001 based on balloon and rocket-borne measurements. A general overview of Odin's water vapour measurements in the middle atmosphere is given. The optimisation of the mesospheric water vapour retrieval is presented in detail.</p><p>The analysis of the observations has focused mainly on different dynamical aspects utilising the characteristic of water vapour as a dynamical tracer in the middle atmosphere. One application is the mesospheric part of the semi-annual oscillation (SAO). The observations reveal that this oscillation is the dominant pattern of variability between 30°S and 10°N in the mesosphere up to an altitude of 80 km. Above 90 km the SAO is dominating at all latitudes in the tropics and subtropics. It is shown that the SAO exhibits a distinct phase change between 75 km and 80 km in the tropical region.</p><p>This thesis also presents the first satellite observations of water vapour in the altitude range between 90 km and 110 km, extending the observational database up into the lower thermosphere. In the polar regions water vapour exhibits the annual maximum during winter time above 95 km, mainly caused by upwelling during this season. This behaviour is different from that observed in the subjacent part of the mesosphere where the annual maximum occurs during summer time.</p><p>The Hygrosonde-2 campaign provided a high resolution measurement of water vapour in the vicinity of the polar vortex edge. This edge prevents horizontal transport causing different water vapour characteristics inside and outside the polar vortex. The observations show that this separating behaviour extends high up into the mesosphere. Small scale transitions in the Hygrosonde-2 profile between conditions inside and outside the vortex coincided with wind shears caused by gravity waves.</p>
54

Combined Platform for Boost Guidance and Attitude Control for Sounding Rockets / Kombinerad Plattform för Ban- och Attiydstyrning av Sondraketer

Abrahamsson, Per January 2004 (has links)
<p>This report handles the preliminary design of a control system that includes both attitude control and boost control functionality for sounding rockets. This is done to reduce the weight and volume for the control system. </p><p>A sounding rocket is a small rocket compared to a satellite launcher. It is used to launch payloads into suborbital trajectories. The payload consists of scientific experiments, for example micro-gravity experiments and astronomic observations. The boost guidance system controls the sounding rocket during the launch phase. This is done to minimize the impact dispersion. The attitude control system controls the payload during the experiment phase. </p><p>The system that is developed in this report is based on the DS19 boost guidance system from Saab Ericsson Space AB. The new system is designed by extending DS19 with software and hardware. The new system is therefore named DS19+. Hardware wise a study of the mechanical and electrical interfaces and also of the system budgets for gas, mass and power for the system are done to determine the feasibility for the combined system. </p><p>Further a preliminary design of the control software is done. The design has been implemented as pseudo code in MATLAB for testing and simulations. A simulation model for the sounding rocket andits surroundings during the experiment phase has also been designed and implemented in MATLAB. The tests and simulations that have been performed show that the code is suitable for implementation in the real system.</p>
55

Observations of water vapour in the middle atmosphere

Lossow, Stefan January 2008 (has links)
Water vapour is the most important greenhouse gas and plays a fundamental role in the climate system and for the chemistry of the Earth's atmosphere. This thesis presents observations of water vapour in the middle atmosphere with a particular focus on the mesosphere. The majority of these observations presented in this thesis have been performed by the Swedish satellite Odin, providing global observations since 2001. Further observations come from the Hygrosonde-2 campaign in December 2001 based on balloon and rocket-borne measurements. A general overview of Odin's water vapour measurements in the middle atmosphere is given. The optimisation of the mesospheric water vapour retrieval is presented in detail. The analysis of the observations has focused mainly on different dynamical aspects utilising the characteristic of water vapour as a dynamical tracer in the middle atmosphere. One application is the mesospheric part of the semi-annual oscillation (SAO). The observations reveal that this oscillation is the dominant pattern of variability between 30°S and 10°N in the mesosphere up to an altitude of 80 km. Above 90 km the SAO is dominating at all latitudes in the tropics and subtropics. It is shown that the SAO exhibits a distinct phase change between 75 km and 80 km in the tropical region. This thesis also presents the first satellite observations of water vapour in the altitude range between 90 km and 110 km, extending the observational database up into the lower thermosphere. In the polar regions water vapour exhibits the annual maximum during winter time above 95 km, mainly caused by upwelling during this season. This behaviour is different from that observed in the subjacent part of the mesosphere where the annual maximum occurs during summer time. The Hygrosonde-2 campaign provided a high resolution measurement of water vapour in the vicinity of the polar vortex edge. This edge prevents horizontal transport causing different water vapour characteristics inside and outside the polar vortex. The observations show that this separating behaviour extends high up into the mesosphere. Small scale transitions in the Hygrosonde-2 profile between conditions inside and outside the vortex coincided with wind shears caused by gravity waves.
56

Combined Platform for Boost Guidance and Attitude Control for Sounding Rockets / Kombinerad Plattform för Ban- och Attiydstyrning av Sondraketer

Abrahamsson, Per January 2004 (has links)
This report handles the preliminary design of a control system that includes both attitude control and boost control functionality for sounding rockets. This is done to reduce the weight and volume for the control system. A sounding rocket is a small rocket compared to a satellite launcher. It is used to launch payloads into suborbital trajectories. The payload consists of scientific experiments, for example micro-gravity experiments and astronomic observations. The boost guidance system controls the sounding rocket during the launch phase. This is done to minimize the impact dispersion. The attitude control system controls the payload during the experiment phase. The system that is developed in this report is based on the DS19 boost guidance system from Saab Ericsson Space AB. The new system is designed by extending DS19 with software and hardware. The new system is therefore named DS19+. Hardware wise a study of the mechanical and electrical interfaces and also of the system budgets for gas, mass and power for the system are done to determine the feasibility for the combined system. Further a preliminary design of the control software is done. The design has been implemented as pseudo code in MATLAB for testing and simulations. A simulation model for the sounding rocket andits surroundings during the experiment phase has also been designed and implemented in MATLAB. The tests and simulations that have been performed show that the code is suitable for implementation in the real system.
57

Matched field processing based geo-acoustic inversion in shallow water

Wan, Lin 15 November 2010 (has links)
Shallow water acoustics is one of the most challenging areas of underwater acoustics; it deals with strong sea bottom and surface interactions, multipath propagation, and it often involves complex variability in the water column. The sea bottom is the dominant environmental influence in shallow water. An accurate solution to the Helmholtz equation in a shallow water waveguide requires accurate seabed acoustic parameters (including seabed sound speed and attenuation) to define the bottom boundary condition. Direct measurement of these bottom acoustic parameters is excessively time consuming, expensive, and spatially limited. Thus, inverted geo-acoustic parameters from acoustic field measurements are desirable. Because of the lack of convincing experimental data, the frequency dependence of attenuation in sandy bottoms at low frequencies is still an open question in the ocean acoustics community. In this thesis, geo-acoustic parameters are inverted by matching different characteristics of a measured sound field with those of a simulated sound field. The inverted seabed acoustic parameters are obtained from long range broadband acoustic measurements in the Yellow Sea '96 experiment and the Shallow Water '06 experiment using the data-derived mode shape, measured modal attenuation coefficients, measured modal arrival times, measured modal amplitude ratios, measured spatial coherence, and transmission loss data. These inverted results can be used to test the validity of many seabed geo-acoustic models (including Hamilton model and Biot-Stoll model) in sandy bottoms at low frequencies. Based on the experimental results in this thesis, the non-linear frequency dependence of seabed effective attenuation is justified.
58

Cellular and peer-to-peer millimeter wave channel sounding in outdoor urban environments

Ben-Dor, Eshar 17 February 2012 (has links)
Millimeter wave (mm-Wave) systems have become very attractive recently as lower frequency spectrums used for mobile device communications have been experiencing a “spectral crunch” due to the dissemination of smartphones. Channel characterization of the outdoor urban environment, where networks for mobile devices require the highest data capacity, has been quite scarce and even non-existent for cellular (rooftop to ground) setting measurements. Our project characterizes the urban environment at 38 GHz in a cellular setting and 38 and 60 GHz in a peer-to-peer setting. A sliding correlator channel sounder with an 800 MHz RF bandwidth at 38 GHz and 1.5 GHz RF bandwidth at 60 GHz was constructed to measure the channel using a bandwidth that is larger than the expected bandwidths of future mm-Wave channels. Directional antennas were utilized during the measurements to imitate mm-Wave systems using beam steering antenna arrays, which also allowed for AOA characterization. Path loss and RMS delay spread statistics are provided. Finally, an outage study was performed to test the outage likelihood in an urban environment with many multi-story buildings. / text
59

Paradigms Optimization for a C-Band COFDM Telemetry with High Bit Efficiency

Skrzypczak, Alexandre, Thomas, Alain, Duponchel, Guillaume 10 1900 (has links)
ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / Systems using single carrier modulations for flight test transmissions perfectly fit noisy and time selective channels. However, the densification of the airport environment now makes the aero channel also frequency selective due to multiple reflections on surrounding buildings, especially while taxiing and taking off. Obviously, this has a direct consequence on hardware resources and user data rates. In such a context, COFDM represents an appealing solution thanks to its inherent robustness to multipath fading channels. But a direct application of an off-the-shelf COFDM standard is not straightforward as these standards are designed for specific channels whose characteristics are quite different from the aero one. That is why we made an experiment at Toulouse-Blagnac airport to jointly sound the channel and qualify a COFDM waveform. This paper then describes the construction of the waveform and the results of the channel sounding. From this, different standard paradigms are compared.
60

On the application of hydroacoustic methods to analyses of the distribution and abundance of pelagic fishes : behavioral and statistical considerations

Appenzeller, Alfred R. (Alfred Rudolf) January 1992 (has links)
This thesis explored the influence of fish behavior and distribution on the accuracy and precision of quantitative estimates of fish biomass and abundance as assessed by hydroacoustic techniques. Rainbow smelt (Osmerus mordax), a pelagic fish known to undertake diel vertical migrations and to exhibit changes in aggregation intensity associated with these movements was used as the model species for this study. The diel vertical migrations of smelt resulted in their potential inaccessibility to the acoustic gear. To obviate this problem a model of the diel migration of smelt based on observations of their behavioral responses to ambient light and water temperatures, was developed and used to time acoustic estimates of fish biomass and abundance to periods when they were unbiased by inaccessibility. Acoustic surveys were then conducted to evaluate the direct influence of fish aggregation on estimates of fish abundance, and to examine the effect of changes in fish distributions on the statistical validity of acoustic analyses. Comparative acoustic surveys, conducted when fish were schooled and dispersed, showed abundance was underestimated by up to 50% when schooling prevailed. The influence of changes in the level of fish patchiness, induced by diel schooling, on the statistical precision of acoustic estimates of abundance and biomass was found to be insignificant. Cluster sampling, a robust approach to the inherent problems of transect sampling created by autocorrelated data series was applied to acoustic data for the first time and its effectiveness was assessed. Cluster sampling yielded estimates of biomass and of abundance that were more precise than were estimates based on the traditional approach of analyzing complete transects.

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