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Tesi en modalitat de compendi de publicacions, (English) This document presents the collection of four manuscripts published during my Doctoral academic formation, which main goal has been the real-time implementation of tools to monitor the ionosphere using Global Navigation Satellite System (GNSS) signals. Despite the fact that there is a vast literature on ionospheric modelling, the state-of-the-art becomes narrow when referring to real-time developments, especially fulfilling precise requirements on accuracy, performance, coverage, and confidence in the generated products. The main contribution of this work to the scientific community is the deployment of ionospheric-related products to monitor in real-time the state of the ionosphere. The first and second publications targeted the implementation of a novel strategy based on a definition of a GNSS Solar Flare (SF) monitor to automatically confirm Solar Flare Effects (Sfe) in geomagnetism. In the first scientific article, it is inspected the methodology used to fine-tune (adapt) a SF monitor, working with an eleven years period of data to statistically correlate detected SF using GNSS signals with respect to SFe. The results demonstrated that the proposed GNSS Solar Flare monitor can confirm Sfe events when traditional Sfe detectors are not able to respond categorically. The second publication details the methodological approach for defining the proposed GNSS Solar Flare monitor, focusing on the theoretical formulation of the Slant Total Electron Content (STEC) obtained. The third contribution used GNSS signals to detect the presence of Medium Scale Travelling Ionospheric Disturbance (MSTID) within a network of permanent GNSS stations that provide the high-accuracy positioning service known as Network-Real-Time Kinematics (NRTK). The effects of a MSTID are characterized in terms of fluctuations in the electron density in the iono- sphere, experienced differently by each one of the GNSS stations used as reference receivers within the NRTK, and resulting in a d, (Español) Este documento se centra en la implementación de herramientas para monitorizar la ionosfera terrestre por medio del uso de señales GNSS. Si bien se puede encontrar una literatura bastante amplia sobre el modelado de la ionosfera, son reducidos los trabajos relacionados con aplicaciones en tiempo real, particularmente si se busca cumplir con requerimientos específicos vinculados con la precisión, el rendimiento, el cubrimiento y la certidumbre de los productos generados. La principal contribución de esta tesis doctoral es la generación en tiempo real de productos para monitorizar el estado de la ionosfera. Las primeras dos publicaciones se centran en el desarrollo de una nueva metodología fundamentada en un detector de Fulguraciones Solares (SF) basado en mediciones GNSS para la confirmación de los efectos de un SF (SFe) detectados por sensores geomagnéticos. En el primer artículo, se expone el procedimiento para el diseño y ajuste del detector GNSS de SF (GNSS-SF), empleando para ello un periodo de once años de datos con los cuales correlacionar estadísticamente SF detectados por medio del detector GNSS y los eventos SFe detectados en magnetismo. Los resultados demuestran que el detector GNSS-SF es capaz de confirmar eventos SFe cuando estos últimos no son categóricamente validados por los instrumentos magnéticos. La segunda publicación detalla el enfoque metodológico desarrollado para definir el detector GNSS-SF que se propone en el artículo. La tercera publicación emplea señales GNSS para detectar la presencia de perturbaciones de escala media que se desplazan en la ionosfera (MSTID) en una red de estaciones GNSS fijas que brindan servicios de posicionamiento muy preciso (NRTK). Los efectos de una MSTID pueden ser caracterizados por medio de la fluctuación en el contenido electrónico de la ionosfera, experimentado de manera diferente por cada una de las estaciones GNSS usadas como referencia dentro del servicio NRTK, ocasionando una degradación en el pos, Postprint (published version)

The Global Navigation Satellite System (GNSS) allows computing the Position, Velocity and Time (PVT) of users equipped with appropriate hardware (i.e. an antenna and a receiver) and software. The latter estimates the PVT from the ranging measurements and ephemeris transmitted by the GNSS satellites in frequencies of the L band. The research group of Astronomy and Geomatics (gAGE) at the Universitat Politecnica de Catalunya (UPC) has been developing the GNSS LABoratory (gLAB) tool suite since 2009, in the context of the European Space Agency (ESA) educational program on satellite navigation (EDUNAV). gLAB is a multi-purpose software capable of determining the PVT in several modes: stand-alone (e.g. as a smartphone or car navigator), differential (e.g. surveying equipment or precise farming), and augmented with integrity (e.g. civil aviation or safety of life applications). gLAB has been designed for two main sets of users and functions. The first one is to educate University students and professionals in the art and science of GNSS data processing. This includes newcomers to the GNSS field that highly appreciate the Graphical User Interface (GUI), the default templates with the necessary configuration or the messages with warnings and errors. The second group of users are those with previous experience on GNSS. Those are interested into a high computation speed, high-accuracy positioning, batch processing and access to the intermediate computation steps. In the present contribution, we present some examples in which gLAB serves as an education platform. The data sets are actual GNSS measurements collected by the publicly available International GNSS Service (IGS), together with other IGS products such as the satellite orbits and clocks broadcast in the navigation message. The proposed methodology and procedures are tailored to understand the effects of different error components in both the Signal in Space (SIS) and the position domain, by activating or deactivating

As the world becomes more complex rapidly having a smart infrastructure is a necessity to be able to manage them remotely by high accuracy. In order to cope with this issue we need to have precise navigation globally which could be challenging in high- and low latitudes then the focus here is on six GNSS (Global Navigation Satellite System) receivers in the arctic region (high latitude) with GLONASS and GPS constellations. The impact of ionospheric scintillation has been characterized based on Sigma Phi, AATR and ROTI, using a database of one year of data in 2014. The thresholds from cumulative distribution function (CDF) of those scintillation parameters at 99% and 99.9% for each station per constellation have been extracted and high scintillation events were detected. The 1-CDF plots of December and July were compared and the seasonal Sigma Phi evolution has been analyzed for different stations per constellation. Moreover the linear correlation between ROTI and Sigma Phi was observed. These correlation indexes highly depend on type of the receiver, location of the receiver and the type of constellation used which will help us to differentiate between the level or impact of scintillation measured for different receivers per constellation. The scintillation events are observed to depend generally on the location of the receiver, period of the day, performance of the receiver, satellite constellation, and ionosphere behaviour. In addition, the impact of data loss in the database analysed has been shown to be relevant and different from station to station. Finally, single frequency PPP could have a higher convergence time in comparison with double frequency PPP according to a preliminary study. Hence, a detailed future work to investigate this issue is proposed.

The research of this dissertation is studying the ionosphere by GPS radio occultation (RO) techniques. It is mainly divided into two parts. The first part focuses on the methodology in electron density profile retrievals from RO measurements. It aims to get more precise profiles from measured data. Classic Abel inversion is a methodology widely used in RO retrievals, and the error introduced by the spherical symmetry assumption is also well recognised. Separability Method (SM) was developed to eliminate this error in previous studies. In this work, the improvement brought by SM corresponding to classic method is checked and validated. The SM does have better performance excluding the Lack of Collocation (LoC) error. The precision of the results is also shown to depend on the accuracy of the supported GIMs, i.e., the more accurate GIMs are used, the better results can be obtained. The error in SM, introduced by the mis-modelling of using the Vertical Total Electron Content (VTEC) instead of ECLEO, the electron content below LEO height, is also checked. The result shows that it has only minor impact on the retrievals. The second part is the climatological study of topside ionosphere/bottomside plasmasphere based on the RO retrievals using SM, and aims to give a general picture of characteristics and features of these two regions in different solar periods, 2007 -- solar minimum, and 2014 – solar maximum. The empirical two-components models of topside profiles, STIP model and CPDH model, used to separate the ionospheric and plasmaspheric contribution to the VTEC measured from ground to global positioning system (GPS) satellite altitudes, are studied and validated. The conditions of applicability of the STIP model are also discussed. The same as other existing empirical models, it shows the picture of topside ionosphere till some limited altitude, which is decided by the Low Earth Orbit (LEO) satellite height used to observe the RO. The model is used to derive transitio, La recerca feta en aquesta dissertació consisteix en l'estudi de la ionosfera mitjançant tècniques d'Ocultació Ràdio (RO) de GPS. La primera part s'enfoca en la metodologia d'extracció de perfils de les mesures RO. L'objectiu és l'obtenció de perfils més precisos mesurats a partir de les dades. La inversió clàssica d'Abel és una metodologia emprada àmpliament en l'obtenció de RO, tant mateix l'error introduït per l'assumpció de simetria també és reconegut. En ordre d'eliminar aquest error en estudis previs el Separability Method (SM) va ser desenvolupat. En el present treball es revisa i es valida la millora en el mètode clàssic aportada per SM. SM té un millor comportament inclús quan s'exclou l'error de Lack of Collocation (CoL). La precisió dels resultats depenen també de l'exactitud del GIM's suportats (p.ex. Com més exacte són els GIM's emprats millor són els resultats obtinguts). L'error de SM introduït pel modelatge incorrecte en utilitzar el Vertical Total Electron Content (VTEC) en lloc del ECLEO (el contingut d'electrons per sota de l'altura LEO) també és revisat. Els resultats mostren que només tenen un impacte mínim en les mesures extretes de RO. La segona part és un estudi de la climatologia de la part superior de la ionosfera I la part inferior de la plasmaesfera basat en l'extracció RO mitjançant SM amb l'objectiu de donar una imatge general de les característiques I tres d'aquestes dues regions en diferents períodes solars; el mínim solar de 2007 i el màxim solar de 2014. Dos models empírics bi-component, el model STIP i el model CPD, utilitzats per separar la contribució de la ionosfera i la plasmaesfera al VTEC, s?han estudiat i validat. Addicionalment també es discuteix sobre les condicions de l'aplicació de STIP. També es fa el mateix amb altres models empírics. Es mostra la imatge de la part superior de la ionosfera fins a un límit definit d'altitud el qual és determinat per l'altitud de satèl·lit Low Earth Orbit (LEO) que s?ha utilitzat per obs, Postprint (published version)

Ground Based Augmentation System (GBAS) is a version of Differential Global Positioning System (DGPS) designed to reliably support airplane's all phase of approach, landing, departure and surface operations. Local ionospheric gradients are major threats to the GBAS, which prevents the advanced use of GBAS. A new monitor for detecting anomalous ionosphere to provide integrity assurance is implemented in this thesis. The monitor is based on the "Fast Initial Response" Cumulative Sum (FIR-CUSUM) quality-assurance method, which is sensitive to the small persistent shifts.

In this project, the study of a methodology for the computation of a reliable estimation sigma_pr_gnd is study. The method presented is intended to be used for the calibration of the GBAS station, using only one day of data. The GBAS station is used for aircraft navigation in the vicinity of an airport, being used for the precision approaches and landing of the aircraft.

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