This study used airborne gravity data, the 2008 Earth Gravity Model (EGM08) and Shuttle Radar Topographic Mission (SRTM) digital elevation data in a ‘Remove-Compute-Restore’ process to determine absolute vertical reference system for Ethiopia. This gives a geopotential height at any isolated field point where there is a Global Navigation Satellite System (GNSS) measurement without reference to a vertical network or a regional datum point. Previously, height was determined conventionally by connecting the desired field point physically to a nearby bench mark of a vertical network using co-located measurements of gravity and spirit levelling. With the use of precise GNSS positioning and a gravity model this method becomes obsolesce. The new approach uses the ‘Remove-Restore’ process to eliminate longer to shorter wavelengths from the measured gravity data using EGM08 and geometrical and condensed gravity models of the SRTM data. This provides small, smooth and localised residuals so that the interpolation and integration involved is reliable and the Stokes-like integral can be legitimately restricted to a spherical cap. A very fast, stable and accurate computational algorithm has been formulated by combining ‘hedgehog’ and ‘multipoint’ models in order to make tractable an unavoidably huge computational task required to remove the effects of about 1.5 billion! SRTM topographic mass elements representing Ethiopia and its immediate surroundings at 92433 point airborne gravity observations. The compute stage first uses an iterative Fast Fourier Transform (FFT) to predict residual gravity at aircraft height as a regular grid on to the surface of the ellipsoidal Earth and then it used a Fourier operation equivalent to Stokes’ integral to transform the localised gravity disturbance to residual potential. The restore process determines the geopotential number on or above the Earth’s surface where practitioners need it by restoring the potential effects of the removed masses. The accuracy of the geopotential number computed from gravity and topography was evaluated by comparing it with the one derived directly from EGM08 and precise geodetic levelling. The new model is in a good agreement across 100 km baseline with a standard deviation of 56 10−2 2 −2 × m s and 39 10−2 2 −2 × m s relative to EGM08 and levelling, respectively ( 10−2 2 −2 m s is approximately equivalent to 1mm of height). The new method provides an absolute geopotential height of a point on or above the Earth’s surface in a global sense by interpolating from geopotential models prepared as the digital grids carried in a chip for use with the GNSS receiver in the field.

Cette thèse porte sur les défis en matière de surveillance de la fiabilité de la navigation par GNSS pour les applications de véhicules terrestres dans les milieux urbains. L'objectif principal de cette recherche est de développer des méthodes de positionnement avec confiance en utilisant des mesures GNSS et des mesures de confiance pour l'utilisateur dans des environnements urbains contraintes. Dans la première partie de la thèse, les erreurs NLOS en milieu urbain sont caractérisées par un modèle 3D de l'environnement urbain. Dans la deuxième partie de la thèse, nous avons proposé une technique de surveillance de la fiabilité dans le domaine des mesures GNSS pour l'environnement urbain en utilisant un capteur de vitesse fiable. Enfin, nous avons développé une nouvelle expérimentale de surveillance de l'intégrité pour le positionnement en milieu urbain. En surveillant de la statistique de test contre un seuil spécifique, l'intégrité et la continuité de positionnement sont fixés à un certain niveau de confiance. En outre, le calcul de niveau de protection horizontale (HPL) en utilisant une approche composite a également été proposé. / This thesis addresses the challenges in reliability monitoring of GNSS aided navigation for land vehicle applications in urban environments. The main objective of this research is to develop methods of trusted positioning using GNSS measurements and confidence measures for the user in constrained urban environments. In the first part of the thesis, the NLOS errors in urban settings are characterized by means of a 3D model of the urban surrounding. For the second part of the thesis, the work proposes a reliability monitoring technique in the range domain for urban environ ment using a trusted velocity sensor. Finally, the research developed a novel experimental scheme in integrity monitoring for positioning in urban environment. By monitoring the test statistic against a specific threshold, the positioning integrity and continuity are met at a certain level of confidence. In addition, the Horizontal Protection Level (HPL) computation using a composite approach has also been proposed.

Global Navigation Satellite Systems (GNSS) are used in a multitude of civilian as well as security related applications. GNSS-receivers are vulnerable to different types of spoofing attacks where the receiver is ``tricked'' to provide false position and time estimates. These attacks could have serious implications; hence, it is important to develop GNSS-receivers that are robust against spoofing attacks. This thesis investigates the use of multiple GNSS-receivers that exchange information such as pseudorange or carrier phase measurements in order to perform spoofing mitigation. It has previously been shown that carrier phase measurements from multiple receivers can be used to identify spoofing signals. The focus in this thesis is on investigating the possibility of using pseudorange measurements from two receivers to perform spoofing mitigation. The use of pseudoranges to perform spoofing mitigation is compared to the use of carrier phases. The spoofing attack is assumed to be performed using a single transmission antenna. This is exploited in order to identify the spoofing signals. The spoofing mitigation algorithms compute, for a pair of receivers, either pseudorange or carrier phase double differences. A double difference is the difference of two single differences for a satellite pair, where the single difference is the difference of pseudoranges or carrier phases measured from one satellite by a pair of receivers. The spoofing mitigation involves the identification of spoofing signals based on these calculated pseudorange or carrier phase double differences. The measurements obtained from identified spoofing signals are not used by the receivers in subsequent computations of position, velocity and time, thereby mitigating the effects of the spoofing attack. The spoofing mitigation algorithms were evaluated with the help of the software-defined GNSS-receiver GNSS-SDR, which was modified to acquire and track both authentic signals and spoofed signals. The spoofing mitigation algorithms were implemented and evaluated in MATLAB. Simulated meaconing attacks were created using a Spirent GNSS simulator. The evaluations indicate that spoofing mitigation is possible using pseudorange measurements from two receivers. However, the performance of the spoofing mitigation algorithms deteriorates for short distances between the receivers when pseudorange measurements are used. The use of carrier phase measurements for spoofing mitigation appears to be more appropriate for short distances between the receivers. The use of pseudoranges enabled quite fast identification of the spoofing signals for larger distances between the receivers. Most spoofing signals are identified within 30 seconds using pseudoranges and for distances larger than 20 meter between the receivers.

Geographically distributed networks of acoustic sensors can be used to identify and localize the origin of acoustic phenomena. One area of use is localization of snipers by detecting the bullet's shock wave and the muzzle blast. At FOI Linköping, this system is planned to be adapted from a wire bounded sensor network into a wireless sensor network (WSN). When changing from wire bounded communication to wireless, the issue of synchronization becomes present. Synchronization can be achieved in multiple ways with different benefits depending of the method of choice. This thesis studies the synchronization method of using the highly accurate clock in Global Navigation Satellite System (GNSS) modules. This synchronization method is developed into an independent time stamping device that can be connected to each sensor in the WSN. This ensure that all sensors are synchronized to Coordinated Universal Time (UTC). The thesis starts with a pre-study where different solutions are investigated and evaluated. After the pre-study, a development stage is begun where the best solution is developed into a model to be easily implemented in the future. The result is a model existing of a microcontroller, a timing module and an ADC with built in filter and amplification.

A la frontière entre l'atmosphère neutre et l'espace, le plasma ionosphérique est le siège de réactions d'ionisation complexes. Le champ magnétique terrestre et les champs électriques induits causent des fluctuations spatiales et temporelles de la concentration électronique. Ces irrégularités ionosphériques entrainent des variations rapides de l'amplitude et de la phase des signaux radioélectriques les traversant, notamment aux hautes latitudes. Ce phénomène est appelé scintillation ionosphérique et il est particulièrement craint par la communauté utilisatrice d'applications GNSS qui nécessite une disponibilité et une intégrité optimales des signaux. Le travail présenté dans cette thèse propose une modélisation complète, à 3 axes d'anisotropie, de la scintillation ionosphérique. Ce modèle est basé sur une approche numérique 3D et 2D, de type écrans de phase, et sur la résolution analytique des équations de propagation, en 3D et en 2D. Ces dérivations originales des variances et des spectres de log-amplitude et de phase ont mis en relief les limites de validité d'un modèle numérique 2D. L'étude de sensibilité menée sur les variances et les spectres ouvre également des perspectives d'inversion des données GNSS pour remonter aux caractéristiques du milieu ionosphérique. / The ionospheric plasma is located at the border between neutral atmosphere and outer space and many complex ionization reactions occur inside this turbulent medium. The Earth magnetic field and induced electric fields cause rapid fluctuations of electron density, both spatially and temporarily. When crossing this turbulent layer, RF signals show fast variations of amplitude and phase, especially at high latitudes. This phenomenon is called ionospheric scintillation and it is particularly feared by air navigation using GNSS services, since it degrades the availability and the integrity of signals. This PhD dissertation presents a complete modeling of the effects of ionospheric scintillation, with 3 anisotropy axes. It is based on a numerical approach using the multiple phase screens technique, both in 3D and 2D schemes, and on the analytical resolution of electromagnetic propagation equation, also both in 3D and 2D configurations. The limits of use of a 2D numerical scheme have been outlined by these original formulations of phase and log-amplitude variances and spectra. This complete modeling associated with a sensitivity study on these variances and spectra opens up interesting perspectives on data inversion, in order to better estimate the physical characteristics of the ionospheric medium.

Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Humanas, Departamento de Geografia, Programa de Pós-graduação, 2018. / A expansão tecnológica nas últimas décadas vem promovendo transformações significativas na sociedade e também na aviação civil, pois é um dos setores que mais se desenvolve no cenário mundial. Para permitir a continuidade do crescimento e os benefícios dele decorrentes, a Organização de Aviação Civil Internacional (ICAO) desenvolveu o conceito CNS/ATM, ainda no início dos anos 80, de forma a estruturar as bases da aviação do futuro. Dentro do conceito, a Navegação Baseada em Performance (PBN) é ferramenta fundamental e tida como prioridade da Organização de Aviação Civil Internacional (ICAO). A PBN utiliza avanços tecnológicos, voos mais curtos, rápidos, seguros, econômicos, menos poluentes e proporciona a maximização do espaço aéreo. Nesse sentido, este estudo tem como objetivos apresentar o processo PBN no Brasil demonstrando a relação com os sistemas de navegação global por satélite e seus sistemas de acréscimo de sinal; as especificações de navegação que são usadas no espaço aéreo nacional; e comparar rotas PBN com rotas convencionais em relação a distâncias, ao consumo de combustível e emissão de dióxido de carbono (CO2) utilizando para isso a metodologia da ICAO de Cálculo de Emissão de Dióxido de Carbono e tendo base a análise multitemporal do tráfego aéreo nacional nos últimos doze anos. Os resultados apontam vantagens expressivas da PBN frente à navegação aérea convencional nos aspectos estudados. Na rota Brasília – Manaus, ao longo de um ano, é possível economizar 438 mil litros de combustível com 821 toneladas de CO2 podendo deixar de serem emitidas à atmosfera. Em um panorama temporal de doze anos, economizar-se-ia aproximadamente 50 milhões de litros de combustível e se evitaria a emissão de 107 bilhões de toneladas de CO2 na rota São Paulo/Congonhas – Rio de Janeiro/Santos Dumont, voando-se exclusivamente em rotas PBN com trajetória direta. Embora as rotas PBN impõem o cumprimento de vários requisitos para sua implementação, elas permitem o incremento de tráfego, a acessibilidade ao espaço aéreo, diminuição de distâncias percorridas, economia de combustível e redução da emissão de dióxido de carbono na atmosfera. / The technological expansion in the last decades has been promoting significant transformations in society and also in civil aviation, since it is one of the sectors that develops most in the world scenario. To enable continuity of growth and the resulting benefits, the International Civil Aviation Organization (ICAO) developed the CNS / ATM concept in the early 1980s in order to structure the aviation bases of the future. Within the concept, Performance Based Navigation (PBN) is a fundamental tool and considered a priority of the International Civil Aviation Organization (ICAO). PBN uses technological advancements, shorter, faster, safer, cheaper, less polluting flights and maximizes airspace. In this sense, this study aims to present the PBN process in Brazil demonstrating the relationship with global satellite navigation systems and their augmentations systems; navigation specifications that are used in national airspace; and compare PBN routes with conventional routes in terms of distances, fuel consumption and carbon dioxide (CO2) emissions using the ICAO Carbon Dioxide Emission Calculation methodology and based on multi-temporal traffic analysis over the last twelve years. The results point to the PBN advantages over conventional air navigation in the studied aspects. On the Brasilia - Manaus route, over a year, it is possible to save 438 thousand liters of fuel with 821 tons of CO2, whose emission can be avoided into the atmosphere. In a twelve-year timeframe, approximately 50 million liters of fuel would be saved and the emission of 107 billion tons of CO2 would be avoided on the São Paulo / Congonhas - Rio de Janeiro / Santos Dumont route, flying exclusively on PBN routes with direct trajectory. Although PBN routes require compliance with so many requirements for their implementation, they allow for increased traffic, accessibility to airspace, reduction of distances traveled, fuel economy and reduction of the emission of carbon dioxide in the atmosphere.

Orientador: João Carlos Chaves / Banca: Paulo de Oliveira Camargo / Banca: Sônia Maria Alves Costa / Resumo: A característica continental do Brasil implica na necessidade de constantes desafios científicos em pesquisas espaciais e tecnológicas, que visam contribuir com o desenvolvimento e ao engajamento de centros de pesquisa nacionais e internacionais, fornecendo instrumentos às atividades espaciais no país e no mundo, ampliando as perspectivas de aplicação das ciências e técnicas geodésicas espaciais como o GPS (Global Positioning System) em diversos setores da sociedade, bem como a compreensão e integração das atividades espaciais desenvolvidas no país em âmbito internacional. Neste contexto, destaca-se a contribuição do IGS (International GNSS Service) com os centros regionais de análise e processamento da rede SIRGAS (Sistema de Referência Geocêntrico para as Américas) os IGS-RNAAC-SIR (IGS Regional Network Associate Analysis Centre for SIRGAS) como o IBGE (Instituto Brasileiro de Geografia e Estatística) no que concerne à manutenção e densificação do SIRGAS, disponibilizando soluções semanais no formato SINEX (Software INdependent EXchange Format), referenciadas ao ITRS (International Terrestrial Reference System), que posteriormente são integradas no contexto de uma solução regional pelo DGFI (Deutsches Geodätiches Forschungsinstitut), com base em modelos e convenções adotadas internacionalmente... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The continental characteristic of Brazil implies in the necessity of constant scientific challenges in space and technological research, that they aim at to contribute with the development and to the engagement of national and international centers of research, supplying instruments to the space activities in the country and the world, enlarging the perspectives of application of the sciences and space geodesic techniques as GPS (Global Positioning System) in diverse sectors of the society, as well as the understanding and integration of the space activities developed in the country in international scope. In this context, it is distinguished contribution of the IGS (International GNSS Service) with the regional processing and analysis center of the SIRGAS network (Geodetic Reference System for Americas) the IGS-RNAAC-SIR (IGS Regional Network Associate Analysis Centre for SIRGAS) as the IBGE (Brazilian Institute of Geography and Statistics) with respect to the maintenance and densificação of the SIRGAS network, providing weekly solutions in format SINEX (Software INdependent EXchange Format), referenced to ITRS (International Terrestrial Reference System), that later are integrated in the context of a regional solution for DGFI (Deutsches Geodätiches Forschungsinstitut), with base in models and conventions adopted internationally... (Complete abstract click electronic access below) / Mestre

Submitted by Cássio da Cruz Nogueira (cassionogueirakk@gmail.com) on 2017-03-16T12:59:03Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_AnaliseComparativaAlturas.pdf: 3769843 bytes, checksum: aae3ae05a49d7a8dee7b94e9822b1fd7 (MD5) / Approved for entry into archive by Edisangela Bastos (edisangela@ufpa.br) on 2017-03-20T15:25:17Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_AnaliseComparativaAlturas.pdf: 3769843 bytes, checksum: aae3ae05a49d7a8dee7b94e9822b1fd7 (MD5) / Made available in DSpace on 2017-03-20T15:25:17Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_AnaliseComparativaAlturas.pdf: 3769843 bytes, checksum: aae3ae05a49d7a8dee7b94e9822b1fd7 (MD5) Previous issue date: 2015-03-31 / O presente trabalho busca realizar uma análise comparativa de dados altimétricos obtidos por topografia (nivelamento trigonométrico), geodésia física (rastreio GNSS) e modelagem matemática (MAPGEO2010), tomando como referência as alturas ortométricas obtidas e transportadas pela primeira técnica (topografia), entre duas Referências de Nível (RN’s) da Rede Altimétrica de Alta Precisão (RAAP), com o objetivo de contribuir em estudos hidrológicos que necessitem de dados altimétricos, na decisão de quais métodos ou técnicas podem ser utilizadas em cada estudo, buscando a simplificação, a economicidade e a celeridade nos trabalhos. A pesquisa mostra que, considerando-se as características de relevo da região dos levantamentos e as variações apresentadas entre as distintas técnicas utilizadas, a aplicação de cada técnica é variável, sendo que nos cálculos do gradiente hidráulico de cursos d´água e da produção de sedimentos em uma pequena bacia hidrográfica através da metodologia RUSLE (Revised Universal Soil Loss Equation) todos os métodos são recomendáveis e no cálculo de áreas de inundação devido ao barramento de curso d´água, mostraram-se inviáveis as técnicas de geodésia e modelagem matemática.. Esta conclusão decorre de que a variabilidade nos resultados de cada estudo hidrológico utilizado é de: 0,003% a 0,385% para os gradientes, de 5,85% a 6,49% para a produção de sedimentos e de 29,71% a 79,23% para áreas de inundação. / This study aims to conduct a comparative analysis of elevation data obtained by topography (trigonometric leveling), physical geodesy (screening GNSS) and mathematical modeling (MAPGEO2010), with reference to those obtained orthometric heights and transported for the first technique (topography), between two Level references (RN's) of High Precision Altimetric Network (RAAP), aiming to contribute in hydrological studies requiring altimetry data in deciding which methods or techniques can be used in each study, seeking the simplification, economic efficiency and the speed in the works. Research shows that, considering the relevant characteristics of the survey region and variations presented between the different techniques used, the application of each technique is variable, and in the calculations of the hydraulic gradient waterways and production sediment in a small watershed through the methodology RUSLE (Revised Universal Soil Loss Equation) all methods are recommended and the calculation of flood areas due to the waterway bus, proved unviable geodesy techniques and mathematical modeling. . This conclusion stems from the variability in the results of each study hydrological used is: 0.003% to 0.385% for gradients of 5.85% to 6.49% for the production of sediment and 29.71% to 79.23% for flood areas.

Tese de mestrado integrado. Engenharia Civil. Faculdade de Engenharia. Universidade do Porto. 2010

<p>Examensarbetet som beskrivs i denna rapport handlar om en ny teknik för att förbättra säkerheten för flygplan i luften och i närheten av flygplatser. Denna teknik benämns ADS-B (Automatic Dependent Surveillance Broadcast), och är tänkt att göra det möjligt för piloter att själva få information om trafik i närområdet. Nuvarande system baserar sig i huvudsak på visuella observationer från flygledare i kontrolltorn samt radarspaning omkring flygplatserna. Med det nuvarande systemet kommer det att bli både dyrt och svårt att upprätthålla en acceptabel nivå på flygsäkerheten när trafiken ökar. </p><p>Arbetet har bedrivits i AerotechTelubs regi i Linköping samt med hjälp ifrån företaget Sectra Wireless Technologies AB. Huvuddelen av arbetet inriktar sig på implementerandet av C-funktioner för att hantera kommunikationen och sammankopplandet av ett tidigare skapat system, för grafikvisning, med en transponder som hanterar ADS-B (tillverkad av Sectra). Målet med detta var att göra förberedande arbete åt AerotechTelub som de förhoppningsvis kommer att kunna använda i ett eventuellt kommande projekt. Rapporten tar upp några standarder som hör till konceptet GP&C (Global Positioning & Communication), samt beskriver de delar som ligger till grund för programmets funktion. </p><p>Examensarbetet har resulterat i ett demonstrationsprogram för att visa hur en lösning av problemet kan se ut. Det har tyvärr inte gått att säkerställa om programmet fungerar till fullo, men genom simuleringar och andra tester har huvuddelen av programmets funktioner gått att verifiera.</p>