APRÈN. Portal de la producció docent del professorat de la UPC

This report uses data from the last three years to conduct a study on the Weddell Sea ionospheric anomaly. The data used for this work was generated by the Ionospheric Model for High Accuracy Services, (IONO4HAS) developed by the Polytechnic University of Catalonia (UPC) research group of Astronomy and Geomatics (gAGE). The Weddell Sea is located near the coasts of Antarctica, south of Argentina and Chile. The Weddell Sea Anomaly (WSA) is a region of the ionosphere where abnormally high Vertical Total Electron Content (VTEC) values appear at night (a time at which low values are expected). The mechanisms and causes of this anomaly are still unknown. The objective of this work is to characterize the nature of the WSA, using the ionospheric data generated by IONO4HAS that was calculated by determining the error the ionosphere incurs in Global Navigation Satellite Systems (GNSS) calculations. A secondary objective of this work is a learning process to understand the workings of GNSS communications, how IONO4HAS can calculate the ionospheric activity with them, and the tools used in data processing for these purposes. In the study, three years' worth of data have been classified and processed using GNU-awk (gawk) and bash scripts. The data acquired from IONO4HAS has values of the activity of the ionosphere on two separate layers, a lower one that accounts for the main electronic content of the ionosphere and a higher one that accounts for plasmapheric content; both layers have data recorded every 300 seconds. The lower layer has 7184 Ionospheric Grid Points (IGPs), and the higher layer has 1800, both of which cover the whole earth. The first results generated to study the WSA are Global Ionospheric Maps (GIMs) that show the average VTEC values at each point of the world, in terms of its Local Time (LT). The LT maps are an innovative approach that show the average VTEC value when each point of the earth is at a certain LT (this actually happens at different instants since it is never the same LT in the entire world). The maximum and minimum daily VTEC values (and the hours at which these occur), together with the daily range of VTEC values, are also calculated and shown in GIMs. All results were also calculated seasonally to better characterize the WSA The results show different behaviors and characteristics of the anomaly in different regions near the Weddell Sea. Each of these regions and their anomalous behavior have been defined; three different sub-anomalies have been identified as the West, Central, and East WSA. Most conclusions have been inferred from the results of the first layer in the ionospheric model, however, the second layer showed some interesting values for the hours at which maximum and minimum daily values occur. The general results are aligned with what is known so far of the WSA.

In the present thesis a study is done regarding the viability and optimization of trajectories to get to the stability region around Lagrange points L4 and L5 from the Earth, specifically from periodic orbits around Lagrange points L1 and L2, in the frame of the circular restricted three-body problem of the Earth-Sun system. The trajectory of a spacecraft inside this stability region around L4 and L5 does not leave it for 1000 years or more and without the necessity of any maneuver, i.e. without fuel consumption. Furthermore, this region offers good positions to observe the Sun, and with that to be able to understand and predict the behaviour of possible space weather events, such as solar flares or coronal mass ejections. This is the set of reasons why this stability region is of scientific interest, so that the objective of the present thesis is to study how to get there in the most optimal way possible. Therefore, the unstable invariant manifolds that arise from the periodic orbits around L1 and L2 are the paths to consider as starting points for the transfer trajectories up to L4 and L5, as they take advantage of the dynamic nature of the circular restricted three-body problem. Once the stability region, the types of trajectories around L4 and L5 and the unstable invariant manifolds have been defined, it has been found that it is possible to reach L4 and L5 with a delta-V budget to perform the impulsive maneuvers of around 260 m/s, with times of flight between 8.5 and 9 years. However, it is possible to decrease the time of flight if the delta-V budget is increased, achieving 6-year transfers with delta-V budgets of around 400 m/s or 4-year transfers with delta-V budgets of around 550 m/s. These results show that there is a large variety of trajectories to choose to get to the equilibrium points L4 and L5, all them comparable, in flight times as well as in delta-V budget, to both current and past interplanetary missions. Therefore, it has been seen that there are lots of reasonable possibilities to send a satellite or a set of missions to these stability regions, in order to carry out observations of the Sun and research about space weather without needing to perform station-keeping maneuvers such as in L1 and L2 during the mission period.

The Circular-Restricted Three-Body Problem (CR3BP) describes the motion of a small celestial body in the gravitational field of two larger bodies. The present study focuses on the application of the CR3BP to the Sun-Earth system. To that end, the governing and defining equations for the CR3BP are described in-depth; and key periodic orbits around the Lagrange Points L1, L2, L4, and L5 are mapped. These last two points, located at the vertices of an equilateral triangle in the rotating frame of reference, are particularly useful for observation and exploration due to their stability. Thus, the L4 and L5 points are the final objective of the present study. The study focuses on optimizing transfer trajectories from the previously mapped orbits around L1 and L2 to orbits around L4 and L5, respectively. The procedures utilized significantly reduce the required delta-V budget to perform these transfers to approximately 3 km/s, a value lower than the minimum requirements for interplanetary transfers departing from Earth. This finding has the potential to open up new opportunities for asteroid science and solar observation based at the equilateral Lagrange Points of the Sun-Earth system; ultimately contributing to advancing the current era of scientific research in the field of astrodynamics.

La erupción del volcán Tonga a las 04:15 UT del 15-01-2022 liberó enormes cantidades de energía a la atmósfera, desencadenando variaciones geofísicas muy significativas no solo en la proximidad inmediata del epicentro sino también a nivel mundial en toda la atmósfera. Estas variaciones se conocen como perturbaciones ionosféricas viajeras (TID, por sus si-glas en inglés), es decir, irregularidades de propagación en forma de onda que alteran el entorno de densidad de electrones y desempeñan un papel importante en la propagación de señales de radio que se propagan a través de la ionosfera. Los fenómenos geomagnéticos e ionosféricos afectan a las comunicaciones, GNSS y otros sistemas de los que depende nuestra sociedad tecnológica. La presente tesis final de máster tiene como objetivo analizar algunas de las características más relevantes de los TIDs (como la velocidad de propagación, el tiempo, etc.) en función de la distancia desde la erupción en las señales del Sistema Global de Navegación por Satélite (GNSS). Primero, evaluando los archivos de Receiver Independent Exchange Format (RINEX), es decir, un formato de intercambio de datos para los datos brutos del sistema de navegación por satélite, y luego, calculando los residuos de preajuste, es decir, los datos de entrada para las ecuaciones de navegación. Con estos datos, se analizarán las TIDs con una serie de índices que muestrean en postproceso la perturbación de la ionosfera, desarrollados por el grupo de investigación de Astronomía y GEomática de la Universitat Politecnica de Cata-lunya (gAGE).

onospheric scintillation consists on rapid fluctuations in the amplitude and phase of electromagnetic signals, which includes those of the Global Navigation Satellite System (GNSS), that can lead to cycle slips and even to a loss of lock on the receiver tracking. Hence, scintillation has become one of the major concerns in navigation and the detection and/or mitigation of its effects is one of the current challenges in achieving precise GNSS navigation. This study is focused in characterizing the ionospheric scintillation phenomenon mainly at high latitudes, although one mid-latitude and one low-latitude station have been included in order to compare the results obtained and to be able to correlate the Total Electron Content (TEC) fluctuations with phase scintillation at all latitudes. This characterization has been done based on the parameters σϕ, ROT IL1 and ROT ILGF , using a database of two years of data, 2014 and 2015, and dividing each of them into three different periods (January to April, May to August, and September to December) in order to better assess the levels of scintillation at each station of the year. Moreover, the results obtained using the signals from two different GNSS satellite constellations (GPS and GLONASS) have been studied and compared. The thresholds for moderate and intense scintillation have been computed from the Cumulative Distribution Functions (CDF) of each scintillation for each station, year, period of the year and GNSS satellite constellation using each parameter at 99% and 99.9% percentiles for moderate and intense levels of scintillation, respectively. Thus, using these thresholds and also using the 1-CDF plots, the seasonal evolution of parameters σϕ and ROT IL1 has been analyzed for different stations per constellation. Furthermore, the correlation between both ROT I parameters and σϕ has been assessed for each station, constellation, year and period of the year. It has been observed that these correlation indexes highly depend on the model of the receiver, location of the receiver and the type of constellation used, fact that will help to differentiate between the level of scintillation measured for different receivers per constellation. The scintillation phenomenon has been observed to depend on: the location of the receiver, period of the year, model of the receiver, GNSS satellite constellation, and obviously the ionosphere behaviour. Finally, the parameter ROT IL1 has been observed to perform better than ROT ILGF at high-latitude stations.

Scintillation is a particular type of space weather disturbance that currently limits the accuracy and availability of the Global Navigation Satellite System. The present final master's thesis aims to study the characteristics of satellite navigation techniques. First, evaluate the impact of scintillation on the frequencies and signals used in space-based navigation systems. For this, the TFM will make use of the Geodetic Detrending technique developed by research group Astronomy and Geomatics of the Universitat Politecnica de Catalunya (gAGE). The final objective of this TFM is to show that, once the scintillation effect has been detected, there are receptors that in combination with certain signals can influence navigation or the study of the atmosphere.

Satellite navigation systems require of knowing satellite positions with a high level of accuracy. Unlike other GNSS constellations, GLONASS ephemeris can not be directly obtained from broadcast navigation messages at any desired epoch. A data post process is required to compute the user solution. The present MSc thesis focuses on implementing an algorithm to compute GLONASS coordinates and clocks at any epoch from the broadcast navigation message and allows its accuracy assessment and error characterization, with respect to precise products. Analyzing the resulting data provides values of coordinate and clock differences for short and long terms. The error characterization procedures give a comparison between different GLONASS satellites, allowing to obtain best and worst cases in relation to their coordinates and clock offsets accuracy.

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 Global Navigation Satelite System, GNSS is a constellation of satellites orbiting around the Earth and transmitting signals that contain ranging codes and navigation data, allowing the user to compute its position and providing a continuous 3D location and timing. With the prediction of over 1.2 billion devices that will use GNSS and a revenue of 54.9 billion Euros just in Europe in 2025, it has become a keystone for Europe and Worlds development in fields so important such as transportation, research, meteorology, agriculture and search and rescue among others. For those reasons is so important to keep improving GNSS techniques such as kinematic and static data processing and develop robust and powerful software. On this master thesis, it has been analysed the navigation results with two of the most advanced GNSS data processing tools that there are available nowadays, the GNSS-Lab tool suite, gLAB developed by the group of Astronomy and GEomatics gAGE in collaboration with the European Space Agency, ESA, and the Real Time Kinematics LIBrary, RTKLIB, developed by the Tokyo University of marine science and technology, with data captured with two mass market GNSS receivers, the Argonaut and the Ublox EVK 7. In the first chapter, it has been explained some guidelines to understand the GNSS and explain what it is and how it works with some examples and then, the mathematical explanation of each kind of GNSS signal used in this master thesis. In the second chapter, it has been analyzed the two main programs used for processing and analyzing GNSS data captured in the experiment, the gLAB, and the RTKLIB. On the third part, it has been explained how the data was captured in the different environments that the data had to face, and also, how the antennas were placed to do the experiment in kinematic and static data acquisition. On the fourth section, it can be seen the methodology used by the author of this master thesis to be able to process and get the results, if the reader deserves to reproduce them, are explained on the fourth part. In the fifth chapter, it can be seen the results, first, it is going to be explained which were the main problems that faced the author when performing the data capture whether static or kinematic and then the navigation results on gLAB data tool and the navigations solutions of the RTKLIB data tool. In the last chapter, it can be seen the conclusions that draw the author of the master thesis after evaluating the results and some future work that could be done.

The aim of this document is to present an analysis of ionospheric scintillation occurrence and effects on GNSS systems. Refractive and diffractive effects have been compared in low and high latitudes using data from NovAtel receivers, owned by the European Space Agency. Also, a software utility has been developed by the author in order to work with the binary files from the receivers.

gLAB és un programari gratuït de codi obert per processar dades GNSS. La primera versió d'aquest programa permet la capacitat de processament complet de dades GPS i la manipulació parcial de dades de Galileo i GLONASS. EGNOS és el sistema europeu d'augmentació per satèl·lit que proporciona integritat i exactitut en posicionament GNSS. Aquesta actualització farà que gLAB sigui una de les poques aplicacions de codi lliure i obert capaços de processar dades de EGNOS.

Introduction: Satellite navigation systems are widely used for today's high accuracy applications demanding the most accurate ranging information obtainable, which is the carrier phase observable. Before the carrier phase observable can be utilized as a range information its inherent integer cycle ambiguity must be resolved. Unfortunately, high dynamics, shadowing and multipath may cause cycle-slips, i.e. jumps of the carrier phase observable by an integer multiple of wavelengths. Any cycle-slip if remained undetected would deteriorate the high ranging and positioning accuracy. Proposal: The objective of this Master Thesis is to design novel algorithms for cycle-slip detector, which must be implemented in a real-time algorithm to detect the cycle-slips for multi-frequency GNSS signals. Moreover, the detector must work either with GPS and Galileo satellite constellations. An efficient validation must be done, also including simulations to ensure the reliability of the entire algorithm.