Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

In Iceland, glaciers cover approximately 11% of the land surface and comprise the country's largest reservoir of freshwater. Increases in summer temperatures since the mid-1980s have led to rapid mass loss from the Icelandic ice caps of 9.5-11.4 Gt/yr, and continuously operating GPS stations nationwide have recorded rapid and accelerating surface uplift. Understanding the behavior of Icelandic ice caps-and their relationship to surface uplift, which is modulated by the rheological structure of the crust and upper mantle-has important implications for water resource management and geohazards analysis. The goals of this study are twofold. First, we aim improve the current estimates of glacial isostatic adjustment (GIA)-related uplift in Iceland and to examine if and how uplift rates have changed over the last several decades. Secondly, we explore the utility of motion recorded by continuously operating Global Positioning System stations (cGPS) as an independent measure of ice cap mass variation over both decadal and annual time scales. We take advantage of the now longstanding cGPS network in Iceland and consider position time series from 62 stations across the entire island. Observations made by cGPS stations from 1995-2014.7 show a broad region of rapid uplift in central Iceland with near zero uplift observed along the coastal regions to the north and west. The most rapid uplift and uplift accelerations occur near the center of the island, between the Vatnajökull and Hofsjökull ice caps, with rates exceeding 30 mm/yr and accelerations of 1-2 mm/yr². Statistically significant uplift and uplift accelerations are recorded at 27 of the 62 cGPS stations, and estimates for the timing of uplift initiation correlate with Arctic warming trends and observations of increasing summer temperatures since the mid-1980s. These results represent a significant improvement over previous uplift estimates and indicate a likely relationship between accelerated ice cap melting and contemporaneous changes in uplift rates. Incorporating cGPS-recorded information about modern-day uplift rates affects estimates of mantle viscosity. Ice cap thinning rates are computed by a weighted least squares estimation scheme utilizing cGPS-derived secular uplift rates and accelerations and Green's functions for an elastic layer over a Maxwell viscoelastic half-space. We test a range of viscosities from 8 x 10¹⁷ and 1 x 10²⁰ Pa·s and find that thinning rates computed with low viscosities between 2 x 10¹⁸ and 1 x 10¹⁹ Pa·s match independently derived ice cap thinning rates best, in accordance with previous upper mantle viscosity estimates. Similar estimation techniques demonstrate the utility of cGPS to provide a seasonal mass variation time series as a potential low-cost compliment to traditional field-based mass balance measurements. We use estimates of secular site velocity and acceleration to reduce the time series and focus only on the annual periodic motion. The increased temporal resolution afforded by the daily cGPS position estimates recovers the interannual variability in the timing and magnitude of accumulation and melt seasons with a small RMS reduction relative to a sinusoidal model. We also find we are able to identify of the effects of both ice cap insulation as well as reduced surface albedo following volcanic eruptions.

The thesis aims to describe and evaluate one of the systems for the fleet monitoring, which is available on the Czech market.The thesis consists of two parts. The first part describes the Global Positioning System GPS and fleet management.The second part discusses of an international monitoring system PosiTrex whose provider is Level Ltd. Interpretation includes a performance of the company, a description of the benefits system and describes the communication units.

A navigation filter simulation and analysis environment was developed through the integration of DRAGON, a high fidelity real-time PNT sensor measurement source, and Scorpion, a modular navigation filter implementation framework. The envi- ronment allows navigation filters to be prototyped and tested in varying complex scenarios with a configurable set of navigation sensors including GNSS and IMU. An analysis of an EKF using the environment showed the utility and functionality of the system.

A navigation filter simulation and analysis environment was developed through the integration of DRAGON, a high fidelity real-time PNT sensor measurement source, and Scorpion, a modular navigation filter implementation framework. The envi- ronment allows navigation filters to be prototyped and tested in varying complex scenarios with a configurable set of navigation sensors including GNSS and IMU. An analysis of an EKF using the environment showed the utility and functionality of the system.

O uso de processos práticos, seguros e rápidos alternativos aos da topografia para medida de altitudes em vias existentes, tornou-se necessário porque: o transporte de cana de açúcar utiliza rodovias e diversos tipos e modelos de caminhões pesados que participam cada vez mais do transporte e provocam a necessidade de reestudo da geometria das vias. O perfil vertical de rodovias é constituído por rampas, concordadas por curvas verticais. A parábola simples de eixo vertical é a forma de curva mais usual para concordar rampas. Analisando resultados de levantamentos de cotas na via Thales de Lorena Peixoto Júnior - SP 318 - demonstrou-se que o Sistema de Posicionamento Global (GPS) - equipamentos e processos para determinar posições em três dimensões na, ou próximo à, superfície terrestre, a partir de sinais transmitidos por satélites artificiais - pode fornecer coordenadas horizontais e verticais para estudo de perfis verticais em rodovias existentes. Conclui-se que dados obtidos com uso do GPS e processados através de análise de regressão, são adequados para \"reconstruir a geometria vertical de vias\", e, que o estudo de pontos extremos de resíduos da análise de regressão de rampas pode levar à redução de erros padrões nas expressões de curvas verticais e rampas. Durante a concessão de Autorização Especial para controlar o acesso de veículos pesados às rodovias oficiais, os Órgãos com jurisdição sobre a via devem analisar itens como a distância de visibilidade nas áreas de manobra para minimizar o risco de acidentes - o GPS pode facilitar esses estudos. / lt can be good to use best methods than Surveying to define the vertical alignment of existing roads specially because the sugar cane and large cargo vehicles are becoming a significant share of the traffic in Brazilian Rural Highways. The Global Positioning Systems (GPS) is a system to determine positions in three dimensions from satellite emitted signals. lt was demonstrated that analyzing elevations obtained by GPS from the Thales de Lorena Peixoto Júnior Highway (Sao Carlos, State of Sao Paulo, Brazil) gives the necessary arguments to conclude that GPS Operations can be a process to study the vertical elevations of constructed highways. The main conclusion of the work is that GPS data can be processed by using regression analysis to reconstruct the vertical alignment of roads. Also the data could express the parabolic vertical curves. To ride a high cargo vehicle in a road one need to have a \"special passport.\" The Public administrator needs to know details on some items from vertical alignments in order to minimize the accidents\' risks for issuing this document - GPS should help the studies on those subjects.

"Orbital flight of CubeSats in extremely Low Earth Orbit, defined here as an altitude between 150 – 250 km, has the potential to enable a wide range of missions in support of atmospheric measurements, national security, and natural resource monitoring. In this work, a mission study is presented to demonstrate the feasibility of using commercially available sensor and electric thruster technology to extend the orbital lifetime of a 3U CubeSat flying at an altitude of 210 km. The CubeSat consists of a 3U configuration and assumes the use of commercially available sensors, GPS, and electric power systems. The thruster is a de-rated version of a commercially available electrospray thruster operating at 2 W, 0.175 mN thrust, and an Isp of 500 s. The mission consists of two phases. In Phase I the CubeSat is deployed from the International Space Station orbit (414 km) and uses the thruster to de-orbit to the target altitude of 210 km. Phase II then begins during which the propulsion system is used to extend the mission lifetime until propellant is fully expended. A control algorithm based on maintaining a target orbital energy is presented in which simulated GPS updates are corrupted with measurement noise to simulate state data which would be available to the spacecraft computer. An Extended Kalman Filter is used to generate estimates of the orbital dynamic state between the 1 Hz GPS updates, allowing thruster control commands at a frequency of 10 Hz. For Phase I, operating at full thrust, the spacecraft requires 25.21 days to descend from 414 to 210 km, corresponding to a ΔV = 96.25 m/s and a propellant consumption of 77.8 g. Phase II, the primary mission phase, lasts for 57.83 days, corresponding to a ΔV = 119.15 m/s during which the remaining 94.2 g of propellant are consumed. "

O uso de processos práticos, seguros e rápidos alternativos aos da topografia para medida de altitudes em vias existentes, tornou-se necessário porque: o transporte de cana de açúcar utiliza rodovias e diversos tipos e modelos de caminhões pesados que participam cada vez mais do transporte e provocam a necessidade de reestudo da geometria das vias. O perfil vertical de rodovias é constituído por rampas, concordadas por curvas verticais. A parábola simples de eixo vertical é a forma de curva mais usual para concordar rampas. Analisando resultados de levantamentos de cotas na via Thales de Lorena Peixoto Júnior - SP 318 - demonstrou-se que o Sistema de Posicionamento Global (GPS) - equipamentos e processos para determinar posições em três dimensões na, ou próximo à, superfície terrestre, a partir de sinais transmitidos por satélites artificiais - pode fornecer coordenadas horizontais e verticais para estudo de perfis verticais em rodovias existentes. Conclui-se que dados obtidos com uso do GPS e processados através de análise de regressão, são adequados para \"reconstruir a geometria vertical de vias\", e, que o estudo de pontos extremos de resíduos da análise de regressão de rampas pode levar à redução de erros padrões nas expressões de curvas verticais e rampas. Durante a concessão de Autorização Especial para controlar o acesso de veículos pesados às rodovias oficiais, os Órgãos com jurisdição sobre a via devem analisar itens como a distância de visibilidade nas áreas de manobra para minimizar o risco de acidentes - o GPS pode facilitar esses estudos. / lt can be good to use best methods than Surveying to define the vertical alignment of existing roads specially because the sugar cane and large cargo vehicles are becoming a significant share of the traffic in Brazilian Rural Highways. The Global Positioning Systems (GPS) is a system to determine positions in three dimensions from satellite emitted signals. lt was demonstrated that analyzing elevations obtained by GPS from the Thales de Lorena Peixoto Júnior Highway (Sao Carlos, State of Sao Paulo, Brazil) gives the necessary arguments to conclude that GPS Operations can be a process to study the vertical elevations of constructed highways. The main conclusion of the work is that GPS data can be processed by using regression analysis to reconstruct the vertical alignment of roads. Also the data could express the parabolic vertical curves. To ride a high cargo vehicle in a road one need to have a \"special passport.\" The Public administrator needs to know details on some items from vertical alignments in order to minimize the accidents\' risks for issuing this document - GPS should help the studies on those subjects.

Tese de Mestrado Integrado. Engenharia Informática e Computação. Faculdade de Engenharia. Universidade do Porto. 2013

The integrated GPS/INS system has become an indispensable tool for providing precise and continuous position, velocity, and attitude information for many positioning and navigation applications. Although the integrated GPS/INS system provides augmented solutions that make use of the complementary features of each component system, its performance is still limited by the quality of GPS measurements, and the geometric strength of the satellite constellation. To address such a problem this research has focussed on the integration of GPS, Pseudolite and INS technologies. The main research contributions are summarised below: (a)A cost effective GPS/INS integration approach has been developed and tested, consisting of a single-frequency L1 GPS receiver and a tactical-grade strapdown INS. Results of field experiments demonstrate that this approach is capable of delivering position accuracies of the order of a few centimetres under a benign operational environment and provides continuously positioning at sub-decimetre accuracy during GPS signal blockage lasting up to about five seconds. (b) A novel kinematic positioning and navigation system based on GPS/Pseudolite/INS integration has been proposed as an alternative to existing GPS/INS systems. With this integration approach, the continuity, integrity, and precision of the GPS/INS system can be significantly improved as the inclusion of pseudolite signals enhances the GPS signal availability and the geometry strength. (c)The impact of pseudolite location errors in such pseudolite-augmented systems has been investigated. Theoretical and numerical analyses reveal that the error effects on measurement models, and on final positioning solutions, can be minimised by selecting optimal pseudolite location(s). (d)A new ambiguity resolution procedure has been developed for use in the proposed GPS/Pseudolite/INS system. It is designed to rapidly and reliably resolve the single-frequency ambiguities due not only to the aiding by pseudolites and INS, but also by adopting a realistic stochastic model and a statistically rigorous ambiguity validation test. The proposed procedure can indeed improve the performance of the single-frequency ambiguity resolution algorithm in terms of both reliability and time-to-fix-ambiguity. (e)An effective cycle slip detection and identification algorithm has been developed, which is suitable for the integrated GPS/Pseudolite/INS system. Test results indicate that induced cycle slips can be reliably detected and instantaneously identified, even if the slips occur at successive epochs. (f)Flight trials have been conducted to evaluate the overall performance for aircraft approach and landing using the GPS/Pseudolite/INS system. Results from these trials show that an enhancement in the accuracy and reliability of the vehicle navigation solution can be achieved with the employment of one or more pseudolite.