This thesis has two major objectives. The first objective is to investigate the seasonal and diurnal variations in occurrence of HF coherent echoes. We assess F-region echo occurrence rates for the PolarDARN HF radars at Inuvik (INV) and Rankin Inlet (RKN) and the auroral zone SuperDARN radars at Saskatoon (SAS) and Prince George (PGR) for the period of 2007-2010. We show that the INV and RKN PolarDARN radars show comparable rates of echo occurrence all the time and they detect 1.5-2.5 times more echoes through ½-hop propagation mode (MLATs=80°-85°) than the SAS and PGR SuperDARN radars through 1½-hope propagation mode (MLATs=75°-80°). For all four radars, the winter occurrence rates are about ~2 times higher than the summer rates. For observations in the dusk, midnight and dawn sectors, equinoctial maxima are evident. The pattern of echo occurrence in terms of MLT/season is about the same for all radars with clear maxima near noon during winters and summers and enhanced (as compared to other time of the day) occurrence rates during equinoctial dusk and dawn hours. Additionally, to investigate the effect of solar cycle on occurrence of F-region echoes, we consider the near noon and near midnight echo occurrence rates for the Saskatoon radar over the period of 1994-2010. We show that there is a strong, by a factor of ~10, increase in SAS night-side echo occurrence towards solar maximum. The effect does not exist for the dayside echoes; moreover, a decrease in number of echoes, by a factor of ~2, was discovered for the declining phase of the solar cycle. The second objective is to evaluate the electron density and the electric field as factors controlling the occurrence of F-region echoes. We use observations of these two ionospheric parameters measured by CADI ionosonde and RKN observations of echo occurrence rates over Resolute Bay (MLAT=83°). We show that there is a correlation in changes of echo occurrence and electron density changes for 3 years of radar-ionosonde joint operation (2008-2010). The comparison of radar-ionosonde data shows that the enhanced echo occurrence at near noon hours during summer months correlate with the enhanced electric field during these periods.

In this thesis, the relationship between several high-latitude phenomena and the ionospheric conductance in both hemispheres is studied theoretically and experimentally. </p>Theoretically, the high-latitude electrodynamics is studied by considering currents in the magnetosphere-ionosphere system resulting from the ionospheric sheet current redistribution between the conjugate ionospheres. It is shown that strong flow between the conjugate ionospheres, the interhemispheric currents (IHC), can be set up if the conductance distribution is asymmetric in the conjugate ionospheric regions. Such conditions are typical for solstices owing to the differences in the solar illumination. Analytical and numerical modeling shows that IHCs can appear in the regions of strong conductance gradient, more specifically around the solar terminator line, and that the intensity of the IHCs can be comparable to the intensity of the well known Region 1/Region 2 currents. The effect of IHC excitation on observable magnetic perturbations on the ground is investigated. It is shown that in the vicinity of the solar terminator line, the pattern of magnetic perturbation can be such that an apparent equivalent current vortex can be detected. In addition, strong conductance gradients are shown to affect significantly the quality of the ionospheric plasma flow estimates from the ground-based magnetometer data. </p>Experimentally, the effect of the nightside ionospheric conductance on occurrence of substorms, global storm sudden commencement and radar auroras is investigated. To characterize substorm occurrence, new parameters, the derivatives of the classical AE and AO indices, are introduced. It is shown that the seasonal and diurnal variations of these parameters are controlled by the total nightside ionospheric conductance in the conjugate regions. The substorm onsets preferentially occur at low levels of the total conductance, which is consistent with the idea of the substorm triggering through the magnetosphere-ionosphere feedback instability. It is hypothesized that the total conductance affects the global storm onsets as well. To check this idea, the 33-year sudden storm commencement (SSC) data are considered. The semiannual, annual, semidiurnal, and diurnal variations in the SSC occurrence rate are found to be significant and these components exhibit a strong relationship with the total conductance of the high-latitude ionospheres. Finally, the SuperDARN midnight echo occurrence is shown to correlate, for some radars, with the total conductance minima and presumably with electric field maxima, which is consistent with general expectation that the F-region irregularities occur preferentially during times of enhanced electric fields. The gradients of the high-latitude conductance can also lead to significant errors in the plasma convection estimates from the ground-based magnetometers, and to investigate this effect a statistical assessment of the difference between the true plasma convection (SuperDARN) and the magnetometer-inferred equivalent convection direction is performed. The largest differences are found for the transition region between the dark and sunlit ionospheres and in the midnight sector where strong conductance gradients are expected due to particle precipitation. Consideration of regular conductance gradients due to solar illumination improves the agreement between the radar and magnetometer data. Finally, an attempt is made to demonstrate the effects of conductance upon the properties of traveling convection vortices (TCVs). Joint SuperDARN and magnetometer data reveal that there is resemblance between the magnetometer and radar inferred TCV images on a scale of thousands of kilometers. However, on a smaller scale of hundreds of kilometers, significant differences are observed.

Los sistemas de posicionamiento global GNSS (GPS y GLONASS) se han convertido en una herramienta básica para obtener medidas geodésicas de la Tierra y en una fuente de datos para el estudio atmosférico. Proporcionan cobertura global y permanente y por la precisión, exactitud y densidad de datos, las señales radio transmitidas pueden ser usadas para la representación espacio-temporal de la atmósfera.La tecnología de los receptores GPS ha evolucionado con una sorprendente rapidez, resultando en instrumentos con suficiente calidad de medida para ser utilizados en estudios geodésicos, comparables a los resultados de técnicas como la interferometría de muy larga base (VLBI), y estudios atmosféricos cuyos resultados pueden ser usados en meteorología.En la tesis Tomografía Atmosférica utilizando Señales Radio de Satélites nos hemos centrado en el uso del sistema GPS por disponer mayor cantidad y calidad de referencias y herramientas para el procesado de los datos. No obstante, se ha demostrado la posibilidad de extender el concepto a cualquier sistema de transmisión radio desde satélite como sondeador atmosférico. La estructura de la tesis se ha dividido en dos áreas: el procesado de datos GPS para extraer información referente a los parámetros atmosféricos de interés, y la aplicación de técnicas tomográficas para la resolución de problemas inversos. En particular, la tomografía se ha aplicado a la ionosfera y la atmósfera neutra. En ambos casos, los resultados tienen un innegable impacto socio-económico: a) la monitorización del estado ionosférico es fundamental por las perturbaciones que la ionosfera provoca en las transmisiones radio que la atraviesan, y b) la estimación del contenido de vapor de agua de la troposfera es de utilidad en la predicción meteorológica y climática.La tomografía ionosférica se empezó a desarrollar usando únicamente datos de la red global IGS. A continuación se mejoró la resolución vertical mediante la utilización de datos de ocultaciones del experimento GPS/MET. La mejora de la resolución se ve limitada a la región en la que estos datos existen. Finalmente, se utilizaron datos de altimetría del satélite TOPEX/POSEIDON para mejorar los mapas y para demostrar la posibilidad de calibración instrumental de los altímetros radar usando técnicas tomográficas.La aplicación a la troposfera se obtuvo tras la mejora y refinamiento tanto del procesado de datos GPS como del proceso de inversión tomográfica. Los primeros resultados se obtuvieron mediante los datos experimentales de la red permanente en Kilauea, Hawaii, por la configuración particular de los receptores. Estos resultados demostraban la capacidad de obtener representaciones espacio-temporales de la troposfera mediante datos GPS. El análisis de los datos de la campaña REGINA, realizada en el Onsala Space Observatory, nos permitió la descripción de un fenómeno meteorológico complejo mediante la tomografía troposférica usando datos GPS y su verificación por comparación directa con medidas realizadas por radiosondeo.En conclusión, se ha demostrado la posibilidad de aplicar tomografía a la atmósfera utilizando señales radio de satélites y, en particular, la constelación GPS. / The Global Navigation Satellite Systems (GPS and GLONASS) have become a basic tool to obtain geodetic measurements of the Earth and a source of data for the atmospheric analysis. Since these systems provide a global, dense and permanent coverage with precise and accurate data, the radio signals they transmit can be used for the spatio-temporal representation of the atmosphere.GPS receivers technology has evolved at a surprising pace: nowadays they have sufficient measurement quality as to be used in geodetic studies, together with other techniques such as the Very Long Base Interferometry (VLBI), and in atmospheric studies whose results can be input into meteorological analysis.In the thesis "Atmospheric Tomography Using Satellite Radio Signals" we have focused on the use of GPS system due to the better quality and quantity of references and tools for the data processing. This notwithstanding, we have proven the possibility to broaden the concept to include any other radio signal transmitting satellite system as an atmospheric sounder. The thesis has been divided into two main areas: GPS data processing to extract the information related to the atmospheric parameters under study, and the implementation of tomographic techniques to the solution of the inverse problem. In particular, tomography has been applied to the ionosphere and to the neutral atmosphere. In both cases, results have a socio-economic impact: a) monitoring the ionosphere is essential for radio transmissions across it because of the perturbations it may produce on the signal, and b) estimating water vapour content in the troposphere is highly useful for meteorological and climate forecastFor the ionospheric tomography we initally only used the data from the global IGS network. Vertical resolution was afterwards improved using the occultation data of the GPS/MET experiment. The improvement, however, was limited to the region where these data existed. Finally, we used altimeter data from the TOPEX/POSEIDON satellite to improve the maps and to prove the radar altimeter calibration capability of the tomographic technique.The application to the troposphere was possible after the improvement and refinement of both the GPS data processing and the tomographic inversion. The first results were obtained using the experimental data from the permanent network in Kilauea, Hawaii. The particular geometry of the receivers in this local network made it highly suited for these initial results, which proved the possibility of obtaining spatio-temporal representations of the troposphere using GPS data. The data analysis of the REGINA campaign, which took place at the Onsala Space Observatory, provided the description of a complex meteorological phenomenon using only GPS data tropospheric tomography. We verified the results with a direct comparison with radiosonde data.Concluding, we have demonstrated the capabilities of atmospheric tomography using satellite radio signals, with particular emphasis on the GPS signals.

In this thesis, the relationship between several high-latitude phenomena and the ionospheric conductance in both hemispheres is studied theoretically and experimentally. </p>Theoretically, the high-latitude electrodynamics is studied by considering currents in the magnetosphere-ionosphere system resulting from the ionospheric sheet current redistribution between the conjugate ionospheres. It is shown that strong flow between the conjugate ionospheres, the interhemispheric currents (IHC), can be set up if the conductance distribution is asymmetric in the conjugate ionospheric regions. Such conditions are typical for solstices owing to the differences in the solar illumination. Analytical and numerical modeling shows that IHCs can appear in the regions of strong conductance gradient, more specifically around the solar terminator line, and that the intensity of the IHCs can be comparable to the intensity of the well known Region 1/Region 2 currents. The effect of IHC excitation on observable magnetic perturbations on the ground is investigated. It is shown that in the vicinity of the solar terminator line, the pattern of magnetic perturbation can be such that an apparent equivalent current vortex can be detected. In addition, strong conductance gradients are shown to affect significantly the quality of the ionospheric plasma flow estimates from the ground-based magnetometer data. </p>Experimentally, the effect of the nightside ionospheric conductance on occurrence of substorms, global storm sudden commencement and radar auroras is investigated. To characterize substorm occurrence, new parameters, the derivatives of the classical AE and AO indices, are introduced. It is shown that the seasonal and diurnal variations of these parameters are controlled by the total nightside ionospheric conductance in the conjugate regions. The substorm onsets preferentially occur at low levels of the total conductance, which is consistent with the idea of the substorm triggering through the magnetosphere-ionosphere feedback instability. It is hypothesized that the total conductance affects the global storm onsets as well. To check this idea, the 33-year sudden storm commencement (SSC) data are considered. The semiannual, annual, semidiurnal, and diurnal variations in the SSC occurrence rate are found to be significant and these components exhibit a strong relationship with the total conductance of the high-latitude ionospheres. Finally, the SuperDARN midnight echo occurrence is shown to correlate, for some radars, with the total conductance minima and presumably with electric field maxima, which is consistent with general expectation that the F-region irregularities occur preferentially during times of enhanced electric fields. The gradients of the high-latitude conductance can also lead to significant errors in the plasma convection estimates from the ground-based magnetometers, and to investigate this effect a statistical assessment of the difference between the true plasma convection (SuperDARN) and the magnetometer-inferred equivalent convection direction is performed. The largest differences are found for the transition region between the dark and sunlit ionospheres and in the midnight sector where strong conductance gradients are expected due to particle precipitation. Consideration of regular conductance gradients due to solar illumination improves the agreement between the radar and magnetometer data. Finally, an attempt is made to demonstrate the effects of conductance upon the properties of traveling convection vortices (TCVs). Joint SuperDARN and magnetometer data reveal that there is resemblance between the magnetometer and radar inferred TCV images on a scale of thousands of kilometers. However, on a smaller scale of hundreds of kilometers, significant differences are observed.

The low latitude tropical ionosphere has been investigated by various researchers using Global Positioning System (GPS). Presently for many civil aviation applications, the ionospheric modeling of the tropical region has gained importance, in particular for flight safety. Since ionosphere is dispersive in nature, dual frequency (L1 = 1575.42 MHz and L2 = 1227.60 MHz) GPS observations can be used to obtain Ionospheric Total Electron Content (TEC). Since TEC varies with local time and geomagnetic latitude, an Ionospheric Modeling Technique using spatial linear approximation of vertical TEC over receiver station has been implemented following Sardon et al. The effects of all the systematic errors due to the satellite plus the receiver (SPR) instrumental biases can reach upto several nanoseconds. (1 TEC is 1016 electrons/m2, 1 ns = 2.86 TEC and 1 TEC = 0.16 m). Hence, to have an accurate estimation of ionospheric TEC, the instrumental biases must also be estimated. This thesis describes a heuristic adaptive Kalman Filtering scheme developed to estimate the TEC, the constants in the linearisation scheme, as well as the above total instrumental biases. The Kalman filter implementation is basically an optimization problem of minimizing the Cost Function J based on the difference between the model output and the measurement, called as the ‘innovation’, scaled by its covariance. In order to obtain the best possible results using the Kalman Filter approach, it is essential to provide appropriate values for the initial state, process and measurement noise covariances (P0, Q and R) respectively, which in general may not be known. Usually manual tuning of the filter parameter is carried out without using the above cost function J! The filter estimates can be highly sensitive to the above chosen statistics and thus these will have to be estimated carefully. Hence, we have utilized the Adaptive Kalman Filtering procedure of Myers and Tapley extended by Gemson and Ananthasayanam. The minimization is carried out by simultaneously estimating the above statistics and the unknown parameters, which include the TEC and the instrumental bias. In addition, A Constant Gain Kalman Filter approach using Genetic Algorithm (GA) has also been developed for the above requirement. It is observed that the steady state gains in KF and AKF approaches are in good match with the constant gains obtained from Genetic Algorithm. Using the above Adaptive Kalman Filtering technique and Constant Gain Kalman Filter approach, vertical TEC values and SPR biases have been estimated from the IGS receiver observations stationed at ISTRAC/ISRO, Bangalore, India. A diurnal TEC variation over Bangalore for a period of one year for 2003 and January 2004 is estimated and reported in this thesis. This approach has also been applied to study the behaviour of the ionosphere over low latitude IGS station at Fortaleza, Brazil data during the great magnetic storm on the 15th July 2000 and the results were found to be consistent with the results of Basu et al. In addition, Using Constant Kalman filter, the TEC enhancement over Indian region has been estimated for the October 2003 Ionospheric storm, and the results were found to be consistent with the reported results in the literature.

WINDMI is a low dimensional plasma physics-based model of the coupled magnetosphere-ionosphere system. The nonlinear system of ordinary differential equations describes the energy balance between the basic nightside components of the system using the solar wind driving voltage as input. Of the eight dynamical variables determined by the model, the region 1 field aligned current and ring current energy is compared to the westward auroral electrojet AL index and equatorial geomagnetic disturbance storm time Dst index. The WINDMI model is used to analyze the magnetosphere-ionosphere system during major geomagnetic storms and substorms which are community campaign events. Numerical experiments using the WINDMI model are also used to assess the question of how much interplanetary shock events contribute to the geoeffectiveness of solar wind drivers. For two major geomagnetic storm intervals, it is found that the magnetic field compressional jump is important to producing the changes in the AL index. Further, the WINDMI model is implemented to compute model AL and Dst predictions every ten minutes using real-time solar wind data from the ACE satellite as input. Real-Time WINDMI has been capturing substorm and storm activity, as characterized by the AL and Dst indices, reliably since February 2006 and is validated by comparison with ground-based measurements of the indices. Model results are compared for three different candidate input solar wind driving voltage formulas. Modeling of the Dst index is further developed to include the additional physical processes of tail current increases and sudden commencement. A new model, based on WINDMI, is developed using the dayside magnetopause and magnetosphere current systems to model the magnetopause boundary motion and the dayside region 1 field aligned current which is comparable to the auroral upper AU index. / text

Após a desativação da técnica SA, a ionosfera tornou-se a principal fonte de erro no posicionamento com GPS. O erro associado à ionosfera é diretamente proporcional ao conteúdo total de elétrons (TEC – Total Electron Content) presente ao longo do caminho da trajetória percorrida pelo sinal na ionosfera e inversamente proporcional ao quadrado da freqüência do sinal. O TEC, e conseqüentemente o erro devido à ionosfera, variam no tempo e no espaço e é influenciado por diversas variáveis, tais como: ciclo solar, época do ano, hora do dia, localização geográfica, atividade geomagnética, entre outros. A região brasileira é um dos locais que apresenta os maiores valores e variações espaciais do TEC e onde estão presentes diversas particularidades da ionosfera, tais como, a anomalia equatorial e o efeito da cintilação ionosférica. Desta forma, é importante a realização de pesquisas que visam estudar o comportamento do TEC, e conseqüentemente do erro devido à ionosfera no Brasil, que é um trabalho complexo devido aos diversos fatores que influenciam a variação do TEC, além das particularidades presentes na região brasileira. Estudos desta natureza podem auxiliar a comunidade geodésica brasileira, e demais usuários do GPS, no entendimento das limitações impostas pela ionosfera nas regiões de interesse. Devido à natureza dispersiva da ionosfera, o estudo do comportamento do TEC no Brasil pode ser realizado utilizando os dados GPS de receptores de dupla freqüência pertencentes à RBMC (Rede Brasileira de Monitoramento Contínuo). Adicionalmente, para uma melhor análise, pode-se também utilizar dados das estações da rede IGS (International GNSS Service) da América do Sul. Esta pesquisa tem como principal meta o estudo do comportamento do erro devido à ionosfera na região brasileira em diferentes situações ionosféricas com base em valores de TEC advindos das estações GPS da RBMC e da rede IGS da América do Sul. Outro objetivo é avaliar a performance e as limitações do Mapa Global da Ionosfera do IGS aplicado no posicionamento por ponto na região brasileira. / In the SA absence, the ionosphere is the largest error source in GPS positioning. The error due to the ionosphere in the GPS observables depends on the signal frequency and Total Electron Content (TEC) in the ionospheric layer. The TEC varies regularly in time and space in relation to the sunspot number, the season, the local time, the geographic position, and others. The Brazilian region is one of the regions of the Earth that presents largest values and space variations of the TEC, being influenced by the equatorial anomaly of ionization and ionospheric scintillation. Therefore, it is important to study the TEC behavior in the Brazilian region. Due to the ionosphere dispersive nature, the TEC behavior in Brazil can be studied using GPS data from RBMC (Rede Brasileira de Monitoramento Contínuo – Brazilian Network for Continuous Monitoring of GPS). Additionally, GPS data from IGS (International GNSS Service) network of the South America can also be used in the experiments. The goal of this research is to study the ionospheric error behavior in the Brazilian region, considering different ionosphere situations, using TEC values computed by GPS data from RBMC and IGS network. Other goal is to evaluate the performance and limitations of Global Ionospheric Map of IGS applied in the GPS point positioning in Brazil.

L'ionosphère du côté nuit de Mars reste encore à ce jour une zone mystérieuse et peu connue de l'environnement Martien. Les déplétions d'électrons suprathermiques sont des structures spécifiques à cette région, observées jusqu'à présent par trois satellites : Mars Global Surveyor (MGS), Mars EXpress (MEX) et Mars Atmosphere and Volatile EvolutioN (MAVEN). Leur étude permet aussi bien l'observation de la structure et de la dynamique de l'ionosphère du côté nuit que celle de l'atmosphère neutre, de la topologie magnétique martienne, ainsi que l'étude de l'échappement atmosphérique de Mars. Des structures aussi différentes que les cornets magnétiques, les couches de courants ou encore le terminateur ultra-violet peuvent être examinées à travers les déplétions d'électrons suprathermiques, de par les mécanismes à l'origine de leur présence du côté nuit de Mars. Le but principal de ma thèse a été de tirer parties des trois jeux de données offerts par les satellites MGS, MEX et MAVEN pour mieux comprendre les mécanismes à l'origine des déplétions d'électrons suprathermiques observées du côté nuit ainsi que leur impact sur la structure et la dynamique de l'ionosphère du côté nuit. Dans cette optique, trois critères simples adaptés à chaque mission ont été développés pour identifier les déplétions d'électrons suprathermiques dans une base de données allant de 1999 à 2017. Une étude statistique a révélé la présence d'une région de transition autour de 170 km d'altitude séparant la région collisionnelle dans laquelle les déplétions d'électrons suprathermiques sont directement dues à l'absorption des électrons par le CO_2 atmosphérique, et la région non-collisionnelle dans laquelle elles sont principalement dues aux boucles fermées de champs magnétique d'origine crustale. La compréhension de ces mécanismes m'a permis d'estimer la localisation du terminateur ultra-violet. Celui-ci est situé en moyenne ~120 km au-dessus du terminateur optique. Cette altitude varie entre le côté soir et le côté matin, et une variation saisonnière est prédite par les modèles atmosphériques. / The nightside ionosphere of Mars still remains an unfamiliar and mysterious place. Nightside suprathermal electron depletions are specific features of this region which have been observed at Mars by three spacecraft to date: Mars Global Surveyor (MGS), Mars EXpress (MEX) and the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Their study enables the observation of the nightside ionosphere structure and dynamics as well as the underlying neutral atmosphere, the specific Martian magnetic topology, and possible conduits for atmospheric escape. Structures as different as magnetic cusps, current sheets or the UV terminator can be investigated through suprathermal electron depletions, due to the processes leading to their observation on the nightside of Mars. The main goal of my PhD has been to use the complementarity of the three missions MGS, MEX, and MAVEN to understand the different mechanisms at the origin of suprathermal electron depletions and their implication on the structure and the dynamics of the nightside ionosphere. In this context, three simple criteria adapted to each mission have been implemented to identify suprathermal electron depletions from 1999 to 2017. A statistical study reveals a transition region near 170 km altitude separating the collisional region where suprathermal electron depletions are directly due to electron absorption by atmospheric CO_2 and the collisionless region where they are mainly due to electron exclusion by closed crustal magnetic field loops. Understanding of these phenomena enables me to estimate the location of the UV terminator. It appears to be located ~120 km above the optical terminator, though this location is different between the dawn and dusk terminator and is expected to vary throughout the different Martian seasons.

Submitted by Paulo Sérgio de Oliveira Júnior null (psergio.jr@hotmail.com) on 2017-11-17T14:41:41Z No. of bitstreams: 1 d_oliveira-jr_ps_thesis.pdf: 14260833 bytes, checksum: ebcb000a304456bb9bc42d8d1ccaa566 (MD5) / Approved for entry into archive by LUIZA DE MENEZES ROMANETTO (luizamenezes@reitoria.unesp.br) on 2017-11-17T17:10:17Z (GMT) No. of bitstreams: 1 oliveirajunior_ps_dr_prud.pdf: 14260833 bytes, checksum: ebcb000a304456bb9bc42d8d1ccaa566 (MD5) / Made available in DSpace on 2017-11-17T17:10:17Z (GMT). No. of bitstreams: 1 oliveirajunior_ps_dr_prud.pdf: 14260833 bytes, checksum: ebcb000a304456bb9bc42d8d1ccaa566 (MD5) Previous issue date: 2017-09-05 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / PPP (Precise Point Positioning) is a positioning method by GNSS (Global Navigation Satellite Systems), based on SSR (State Space Representation) concept that can provide centimeter accuracy solutions. Real-time PPP (RT-PPP) is possible thanks to the availability of precise products, for orbits and clocks, provided by the International GNSS Service (IGS), as well as by its analysis centers such as CNES (Center National d'Etudes Spatiales). One of the remaining challenges on RT-PPP is the mitigation of atmospheric effects (troposphere and ionosphere) on GNSS signals. Thanks to recent improvements in atmospheric models, RT-PPP can be enhanced, allowing accuracy and centimeter initialization time, comparable to the current NRTK (Network Real-Time Kinematic) method. Such performance depends on topology of permanent stations networks and atmospheric conditions. The main objective of this project is to study the RT-PPP and the optimized infrastructure in terms of costs and benefits to realize the method using atmospheric corrections. Therefore, different configurations of a dense and regular GNSS network existing in France, the Orpheon network, are used. This network has about 160 sites and is owned by Geodata-Diffusion (Hexagon Geosystems). The work was divided into two main stages. Initially, ‘float PPP-RTK’ was evaluated, it corresponds to RT-PPP with improvements resulting from network corrections, although with ambiguities kept float. Further on, network corrections are applied to improve “PPP-RTK” where ambiguities are fixed to their integer values. For the float PPP-RTK, a modified version of the RTKLib 2.4.3 (beta) package is used to take into account for the network corrections. First-order ionospheric effects were eliminated by the iono-free combination and zenith tropospheric delay estimated. The corrections were applied by introducing a priori constrained tropospheric parameters. Periods with different tropospheric conditions were chosen to carry out the study. Adaptive modeling based on OFCs (Optimal Fitting Coefficients) has been developed to describe the behavior of the troposphere, using estimates of tropospheric delays for Orpheon stations. This solution allows one-way communication between the server and the user. The quality of tropospheric corrections is evaluated by comparison to external tropospheric products. The gains achieved in convergence time to 10 centimeters accuracy were statistically quantified. Network topology was assessed by reducing the number of reference stations (up to 75%) using a sparse Orpheon network configuration to perform tropospheric modeling. This did not degrade the tropospheric corrections and similar performances were obtained on the user side. In the second step, PPP-RTK is realized using the PPP-Wizard 1.3 software and CNES real-time products for orbits, clocks and phase biases of satellites. RT-IPPP (Real-Time Integer PPP) is performed with estimation of tropospheric and ionospheric delays. Ionospheric and tropospheric corrections are introduced as a priori parameters constrained to the PPP-RTK of the user. To generate ionospheric corrections, it was implemented a solution aligned with RTCM (Real-Time Maritime Services) conventions, regarding the transmission of ionospheric parameters SSR, which is a standard Inverse Distance Weighting (IDW) algorithm. The choice of the periods for this experiment was made mainly with respect to the ionospheric activity. The comparison of the atmospheric corrections with the external products and the evaluation of different network topologies (dense and sparse) were also carried out in this stage. Statistically, the standard RT-IPPP takes ~ 25 min to achieve a 10 cm horizontal accuracy, which is significantly improved by our method: 46% (convergence in 14 min) with dense network corrections and 24% (convergence in 19 min) with the sparse network. Nevertheless, vertical positioning sees its convergence time slightly increased, especially when corrections are used from a sparse network solution. However, improvements in horizontal positioning due to external SSR corrections from a (dense or sparse) network are promising and may be useful for applications that depend primarily on horizontal positioning. / O PPP (Precise Point Positioning) é um método de posicionamento pelo GNSS (Global Navigation Satellite Systems), baseado no conceito SSR (State Space Representation) o qual pode fornecer soluções de acurácia centimétrica. O PPP em tempo real (RT-PPP) é possível graças à disponibilidade de produtos precisos, para órbitas e relógios, fornecidos pelo IGS (International GNSS Service), bem como por seus centros de análise, como o CNES (Centre National d’Etudes Spatiales). Um dos desafios restantes no RT-PPP é a mitigação dos efeitos atmosféricos (troposfera e ionosfera) nos sinais GNSS. Graças às melhorias recentes nos modelos atmosféricos, o RT-PPP pode ser aprimorado, permitindo tempo de inicialização com acurácia centimétrica, comparável ao atual método NRTK (Network Real-Time Kinematic). Esse desempenho depende da topologia das redes de estações permanentes e das condições atmosféricas. O objetivo principal deste projeto é estudar o RT-PPP e a infraestrutura optimizada em termos de custos e benefícios para realizar o método usando correções atmosféricas. Portanto, são utilizadas diferentes configurações de uma rede GNSS densa e regular existente na França, a rede Orphéon. Esta rede tem cerca de 160 estações, sendo propriedade da Geodata-Diffusion (Hexagon Geosystems). O trabalho foi dividido em duas etapas principais. Inicialmente, foi avaliado o "float PPP-RTK", que corresponde ao RT-PPP com melhorias resultantes de correções de rede, embora mantendo as ambiguidades como float. Em um segundo momento, as correções de rede são aplicadas para aprimorar o "PPP-RTK", onde ambiguidades são fixadas para seus valores inteiros. Para o float PPP-RTK, uma versão modificada do software RTKLib 2.4.3 (beta) é empregada de modo a levar em consideração as correções de rede. Os efeitos ionosféricos de primeira ordem são eliminados pela combinação iono-free e atraso zenital troposférico é estimado. As correções são aplicadas introduzindo parâmetros troposféricos a priori injuncionados. Períodos com diferentes condições troposféricas foram escolhidos para realizar o estudo. Uma modelagem adaptativa baseada em OFCs (Optimal Fitting Coefficients) foi implementada para descrever o comportamento da troposfera, utilizando estimativas de atraso troposférico para estações da rede Orphéon. Tal solução permite a comunicação unidirecional entre o servidor e o usuário. A qualidade das correções troposféricas foi avaliada através de comparação com produtos externos troposféricos. Os ganhos alcançados no tempo de convergência para acurácia de 10 centímetros foram quantificados estatisticamente. A topologia de rede foi avaliada reduzindo o número de estações de referência (em até 75%) usando uma configuração da rede Orphéon esparsa para realizar a modelagem troposférica. Isso não degradou as correções troposféricas e foram obtidas performances similares para os usuários simulados. Na segunda etapa, o PPP-RTK é realizado usando o software PPP-Wizard 1.3, bem como os produtos para tempo real do CNES de órbitas, relógios e biases de fase dos satélites. O RT-IPPP (Real-Time Integer PPP) é realizado com estimativa de atrasos troposféricos e ionosféricos. As correções ionosféricas e troposféricas são introduzidas como parâmetros a priori injuncionados no PPP-RTK do usuário. Para gerar correções ionosféricas, foi implementada uma solução alinhada com as convenções RTCM (Real-Time Maritime Services), em relação à transmissão de correções ionosféricas SSR, o qual é um algoritmo baseado na ponderação pelo inverso da distância (IDW – Inverse Distance Weighting). A escolha dos períodos para este experimento foi realizada principalmente em relação à atividade ionosférica. A comparação das correções atmosféricas com produtos externos, assim como a avaliação de diferentes topologias de rede (densa e esparsa) também foram realizadas nesta etapa. Estatisticamente, o RT-IPPP padrão leva ~ 25 min para alcançar uma acurácia horizontal de 10 cm, a qual é significativamente melhorada pelo método implementado: 46% (convergência em 14 min) com correções de rede densa e 24% (convergência em 19 min) com a rede esparsa. No entanto, o posicionamento vertical vê o seu tempo de convergência ligeiramente aumentado, especialmente quando as correções são usadas a partir de uma solução de rede esparsa. No entanto, as melhorias no posicionamento horizontal com o uso das correções de SSR externas de uma rede (densa ou esparsa) são promissoras e podem ser úteis para aplicações que dependem principalmente do posicionamento horizontal. / Le PPP (Precise Point Positioning) est une méthode de positionnement par GNSS (Global Navigation Satellite Systems), basée sur le concept SSR (State Space Representation), qui peut générer solutions de précision centimétrique. Le PPP en temps réel (RT-PPP) est possible grâce à la disponibilité des produits précis, pour les orbites et horloges, fournis par l’IGS (International GNSS Service), ainsi que par ses centres d'analyse, tels que le CNES (Centre National d'Etudes Spatiales). Un des défis restants sur le RT-PPP est la mitigation des effets atmosphériques (troposphère et ionosphère) sur les signaux GNSS. Grâce aux améliorations récentes des modèles atmosphériques, le RT-PPP peut être amélioré, ce qui permet une précision et un temps d'initialisation au niveau du centimètre, comparables à la méthode NRTK (Network Real-Time Kinematic) actuelle. De telles performances dépendent de la topologie du réseau de stations GNSS permanentes et des conditions atmosphériques. L'objectif principal de ce projet est d'étudier le RT-PPP et l'infrastructure optimisée en termes de coûts et d'avantages pour réaliser la méthode en utilisant des corrections atmosphériques. Pour cela, différentes configurations d'un réseau GNSS dense et régulier existant en France, le réseau Orphéon, sont utilisées. Ce réseau compte environ 160 sites, propriété de Geodata-Diffusion (Hexagon Geosystems). Le travail est divisé en deux étapes principales. Dans un premier temps, le mode «PPP-RTK flottant» a été évalué, il correspond au RT-PPP avec des améliorations issues des corrections de réseau, mais avec les ambiguïtés flottantes. Ensuite, des corrections de réseau sont appliquées pour améliorer le mode « PPP-RTK » où les ambiguïtés sont fixées à leurs valeurs entières. Pour le PPP-RTK flottant, une version modifiée du package RTKLib 2.4.3 (beta) est utilisée pour prendre en compte les corrections réseau. Les effets ionosphériques de premier ordre ont été éliminés par la combinaison iono-free et le retard troposphérique zénithal est estimé. Les corrections ont été appliquées en introduisant des paramètres troposphériques a priori contraints. Des périodes avec différentes conditions troposphériques ont été choisies pour réaliser l'étude. Une modélisation adaptative basée sur les OFCs (Optimal Fitting Coefficients) a été mise en place pour décrire le comportement de la troposphère, en utilisant des estimations des retards troposphériques pour les stations Orphéon. Cette solution permet une communication mono-directionnelle entre le serveur et l'utilisateur. La qualité des corrections troposphériques est évaluée par comparaison avec des produits troposphériques externes. Les gains réalisés sur le temps de convergence pour obtenir un positionnement de 10 centimètres de précision ont été quantifiés statistiquement. La topologie du réseau a été évaluée, en réduisant le nombre de stations de référence (jusqu'à 75%), via une configuration de réseau Orphéon lâche pour effectuer la modélisation troposphérique. Cela n'a pas dégradé les corrections troposphériques et des performances similaires ont été obtenues du côté de l'utilisateur. Dans la deuxième étape, le PPP-RTK est réalisé grâce au logiciel PPP-Wizard 1.3 et avec les produits temps réel CNES pour les orbites, les horloges et les biais de phase des satellites. Le RT-IPPP (Real-Time Integer PPP) est réalisé avec estimation des délais troposphériques et ionosphériques. Les corrections ionosphériques et troposphériques sont introduites en tant que paramètres a priori contraints au PPP-RTK de l'utilisateur. Pour générer des corrections ionosphériques, il a été mis en place une solution alignée avec les conventions RTCM (Real-Time Maritime Services) pour la transmission des paramètres ionosphériques SSR, un algorithme standard d'interpolation à distance inversée (IDW – Inverse Distance Weighting). Le choix des périodes pour cette expérience a été fait principalement en regard de l'activité ionosphérique. La comparaison des corrections atmosphériques avec les produits externes et l'évaluation de différentes topologies de réseau (dense et lâche) ont également été effectuées dans cette étape. Statistiquement le RT-IPPP standard prend ~25 min pour atteindre une précision horizontale de 10 cm, ce que nous améliorons significativement par notre méthode : 46% (convergence en 14 min) avec le réseau dense et 24% (convergence en 19 min) avec le réseau restreint. Néanmoins le positionnement vertical voit son temps de convergence légèrement augmenté, en particulier lorsque l'on utilise des corrections à partir d'une solution de réseau lâche. Cependant, les améliorations apportées au positionnement horizontal dues aux corrections atmosphériques SSR externes provenant d’un réseau (dense ou lâche) sont prometteuses et peuvent être utiles pour les applications qui dépendent principalement du positionnement horizontal. / CNPq: 229828/2013-2

Ce travail a pour objet d’étudier les variations régulières de l’ionosphère aux moyennes et basses latitudes ainsi que l’impact de différents événements solaires sur l’ionisation. Pour quantifier ces variations, nous utiliserons les réseaux GPS qui permettent de mesurer le Contenu Total Electronique (TEC).Ce travail s’inscrit dans le cadre du projet ISWI. L’étude comprendra une analyse morphologique sur les variations régulières de l’ionisation en période de soleil calme (variation diurne, saisonnière et en fonction du cycle solaire) par le traitement de stations GPS en Europe et en Afrique sur la période analysée (2000 à 2014);les variations perturbées de l’ionosphère associées à des événements solaires retenus selon une grille de critères; L’analyse de l’indice ROTI afin d’étudier les scintillations ionosphériques génératrices d’une dégradation du positionnement aux basses latitudes et en particulier en Afrique.L’étude se poursuivra par la comparaison avec les modèles existants afin d’identifier leurs performances:le modèle NeQuick2, logiciel de modélisation du profil vertical médian l’ionosphère,Le modèle IONEX/CODG qui est une cartographie journalière du TEC en des positions spatiales et temporelles particulières et issu du post-traitement des mesures GPS sur une couverture mondiale.Le troisième volet de cette étude sera de donner des perspectives pour une éventuelle prévision de l’impact d'événements solaires particuliers sur l’ionosphère, par exemple la modélisation des gradients en période magnétiquement perturbée et la prévision de la présence du phénomène de scintillation ionosphérique sur certains trajets satellite-sol. / This work aims to study the regular variations of the ionosphere at middle and low latitudes and the impact of various events on solar ionization. To quantify these changes, we will use GPS networks to measure the Total Electronic Content (TEC) .This work is part of the project ISWI. The study will include a morphological analysis on regular variations in the ionization time of the Quiet Sun (diurnal variation, seasonal and based on the solar cycle) for the treatment of GPS stations in Europe and Africa over the period analyzed (2000 to 2014); variations disturbed ionosphere associated with solar events selected according to a set of criteria; Analysis of the ROTI index to study the ionospheric scintillation generating degradation positioning at low latitudes and especially Africa.The study will continue with the comparison with existing models in order to identify their performance: the NeQuick2 model modeling software profile of the median vertical ,the ionospheric model IONEX / CODG which is a daily mapping TEC in specific spatial and temporal positions and from the post-processing of GPS measurements on a third coverage mondiale.The component of this study will give prospects for a possible anticipation of the impact of specific solar events on the ionosphere, such modeling gradients in magnetically disturbed period and prediction of the presence of ionospheric scintillation event on some ground-satellite paths.