A New Ionospheric Model (ANIMo) based upon the physics of production, loss, and vertical transport has been developed. The model is driven by estimates of neutral composition, temperature and solar flux and is applicable to the mid-latitude regions of the Earth under quiet and moderate geomagnetic conditions. This model was designed to exhibit specific features that were not easy to find all together in other existing ionospheric models. ANIMo needed to be simple to use and interact with, relatively accurate, reliable, robust and computationally efficient. The definition of these characteristics was mostly driven by the intention to use ANIMo in a Data Assimilation (DA) scheme. DA or data ingestion can be described as a technique where observations and model realizations, called background information, are combined together to achieve a level of accuracy that is higher than the accuracy of the two elements taken separately. In this project ANIMo was developed to provide a robust and reliable background contribution. The observations are given by the Global Positioning System (GPS) ionospheric measurements, collected from several networks of GPS ground-station receivers and are available on on-line repositories. The research benefits from the Multi-Instrument Data Analysis System (MIDAS) [Mitchell and Spencer, 2003; Spencer and Mitchell, 2007], which is an established ionospheric tomography software package that produces three dimensional reconstructions of the ionosphere starting from GPS measurements. Utilizing ANIMo in support of MIDAS has therefore the potential to generate a very stable set-up for monitoring and study the ionosphere. In particular, the model is expected to compensate some of the typical limitations of ionospheric tomography techniques described by Yeh and Raymund [1991] and Raymund et al. [1994]. These are associated with the lack of data due to the uneven distribution of ground-based receivers and limitations to viewing angles. Even in regions of good receiver coverage there is a need to compensate for information on the vertical profile of ionisation. MIDAS and other tomography techniques introduce regularization factors that can assure the achievement of a unique solution in the inversion operation. These issues could be solved by aiding the operation with external information provided by a physical model, like ANIMo, through a data ingestion scheme; this ensures that the contribution is completely independent and there is an effective accuracy improvement. Previously, the limitation in vertical resolution has been solved by applying vertical orthonormal functions based upon empirical models in different ways [Fougere, 1995; Fremouw et al., 1992; Sutton and Na, 1994]. The potential for the application of a physical model, such ANIMo is that it can provide this information according to the current ionospheric conditions. During the project period ANIMo has been developed and incorporated with MIDAS. The result is A New Ionospheric Data Assimilation System (ANIDAS); its name suggests that the system is the implementation of ANIMo in MIDAS. Because ANIDAS is a data ingestion scheme, it has the potential to be used to perform not only more accurate now-casting but also forecasting. The outcomes of ANIDAS at the current time can be used to initialise ANIMo for the next time step and therefore trigger another assimilation turn. In future, it is intended that ANIMo will form the basis to a new system to predict the electron density of the ionosphere – ionospheric forecasting.

A novel approach to ionospheric imaging with the purpose of weather/distaster prediction and climate study is introduced. This feasibility study combines traditional material imaging techniques with high frequency (HF) radio via SDR (software defined radio) systems in order to capture three-dimensional images of the atmosphere. An experiment is devised and the necessary instrumentation built in order to capture coherent images of the ionosphere. The experimental results show these three-dimensional images as well as a novel approach to measuring ionospheric height. The novelty of the research comes from the use of a closely spaced phased-array of radio antennas in conjunction with a post-correlation beamformer repurposed from radio astronomy. Experiments were run at both the University of Victoria and DRAO (Dominion Radio Astrophysical Observatory), the results which led to a successful proposal for extending the research onto a larger array with support from research groups in New Mexico. / Graduate

A determinação das coordenadas de um ponto através do sistema GPS pode ser feita utilizando-se os métodos de posicionamento por ponto simples ou de posicionamento diferencial. No caso do posicionamento diferencial, devido à escassez de marcos geodésicos no território nacional, as linhas de base são em sua maioria extensas. Nessas duas situações os usuários de receptores de simples freqüência ficam sujeitos à utilização de modelos ionosféricos para estimativa da influência da ionosfera nos sinais e conseqüentemente na precisão da posição de pontos. Sendo assim, a escolha adequada de tal modelo vem a ser um importante fator a ser considerado durante o processamento dos dados. Neste trabalho foi feita a comparação de resultados de processamento de dados GPS obtidos com a utilização de diferentes modelos ionosféricos a partir de posicionamento por ponto simples, verificando a eficácia de cada um deles em função da latitude do ponto, da atividade solar e do horário do dia, a fim de determinar qual modelo é mais eficiente em cada situação. Para isto foi desenvolvido um programa para posicionamento por ponto simples em linguagem Visual Basic versão 5.0. / The determination of point coordinates, through GPS system, could be made by methods of single point positioning or relative positioning. In this last case, due to geodetic landmarks scarcity in national territory, the baselines are, in its majority, extensive. In these two situations, the users of single frequency receivers are submitted to the use of ionospheric models to estimate the influence of the ionosphere in the signs. Being thus, the adequate choice of such model comes to be an important factor to be considered during the data processing. In this paper was made a matching of results of GPS data processing with the use of different ionospheric models through single point positioning, verifying the efficiency of each model to point latitude, solar activity and time, to determine each model is efficientier at each situation. To this it was developed a single point positioning program in Visual Basic version 5.0.

A determinação das coordenadas de um ponto através do sistema GPS pode ser feita utilizando-se os métodos de posicionamento por ponto simples ou de posicionamento diferencial. No caso do posicionamento diferencial, devido à escassez de marcos geodésicos no território nacional, as linhas de base são em sua maioria extensas. Nessas duas situações os usuários de receptores de simples freqüência ficam sujeitos à utilização de modelos ionosféricos para estimativa da influência da ionosfera nos sinais e conseqüentemente na precisão da posição de pontos. Sendo assim, a escolha adequada de tal modelo vem a ser um importante fator a ser considerado durante o processamento dos dados. Neste trabalho foi feita a comparação de resultados de processamento de dados GPS obtidos com a utilização de diferentes modelos ionosféricos a partir de posicionamento por ponto simples, verificando a eficácia de cada um deles em função da latitude do ponto, da atividade solar e do horário do dia, a fim de determinar qual modelo é mais eficiente em cada situação. Para isto foi desenvolvido um programa para posicionamento por ponto simples em linguagem Visual Basic versão 5.0. / The determination of point coordinates, through GPS system, could be made by methods of single point positioning or relative positioning. In this last case, due to geodetic landmarks scarcity in national territory, the baselines are, in its majority, extensive. In these two situations, the users of single frequency receivers are submitted to the use of ionospheric models to estimate the influence of the ionosphere in the signs. Being thus, the adequate choice of such model comes to be an important factor to be considered during the data processing. In this paper was made a matching of results of GPS data processing with the use of different ionospheric models through single point positioning, verifying the efficiency of each model to point latitude, solar activity and time, to determine each model is efficientier at each situation. To this it was developed a single point positioning program in Visual Basic version 5.0.

Earth's plasmasphere persists as an extension of the ionosphere into space. The toroidal region of plasma is shaped by electric and magnetic forces in the terrestrial magnetosphere. As a dense population of cold plasma, the plasmasphere interacts with particles in the hot ring current and energetic radiation belts. Evolution of plasmaspheric density under the driving influence of the solar wind crosses many physical scales. Convective erosion during geomagnetic storms occurs on the order of hours, reducing the size of the plasmasphere by forming an abrupt plasmapause density gradient that varies in radial and diurnal location. The history of geomagntic activity determines the presence of morphological structures as small as notches and as large as plumes. Plasma of atmospheric origin is carried sunward by convection through drainage plumes towards the magnetopause where it can diminish the effectiveness of magnetic reconnection. Long-lived plumes are sustained by a higher rate of refilling than typically observed during plasmasphere recovery from geomagnetic disturbances. The response of the plasmasphere, then, is an integral part of the feedback cycle between the magnetosphere and ionosphere in the exchange of energy and particles. This thesis aims to address three questions concerning the nature of the plasmasphere through the development of empirical and physics-based models under recent observations provided by the Van Allen Probes (RBSP-A & -B). First, what is the distribution of density content in the plasmasphere? For a two year period with full MLT coverage by RBSP, the upper-hybrid resonance frequency in plasma wave spectra is used to identify sudden changes consistent with the plasmapause feature and to calculate the magnetic equatorial electron density. Plasmapause encounter radial locations for both spacecraft are correlated with a geomagnetic activity index showing significant scatter around a linear fit. On average, the predicted plasmapause location does account for the separation between the saturated plasmasphere and the depleted plasmatrough. A density threshold corresponding to the plasmapause boundary is used to sort RBSP measurements into these two classified plasma regions. Model profiles are developed for each region and compared to the results from previous missions. The importance of solar wind properties in regulating the severity of plasmasphere erosion is demonstrated. Second, how does the plasmapause form and vary with geomagnetic activity? The two-dimensional plasmasphere density model, RAM-CPL, is employed to simulate two geomagnetic storms observed by the RBSP spacecraft. Inner-magnetospheric convection is parameterized by the Kp-index and solar wind properties. The performance of RAM-CPL is evaluated by the correspondence between virtual and actual plasmapause encounters. Overall, RAM-CPL achieved good agreement with RBSP observations of the plasmapause to within 0.5 L and measurements of electron density to within one order of magnetude inside the plasmasphere. An empirical model of ring current-ionosphere feedback was included to account for asymmetric erosion, but did not contribute significantly in the MLT sectors of interest when compared to electric field measurements. The difference in background activity level during quiet conditions between the two convection parameterizations was found to lead to 1 L difference in plasmapause location for each simulation trial. Solar wind driven simulations produce sharper and deeper erosion of the plasmapause at the onset of a geomagnetic storm, but also allow for larger recovery of the plasmasphere when compared to Kp-index driven simulations. Third, what is the role of the ionosphere in sustaining the plasmasphere? Four geomagnetic events are observed by RBSP in opposing MLT sectors to exhibit undisturbed plasmasphere refilling following significant erosion of the plasmapause. RAM-CPL simulations of the strongest storm parameterized by solar wind properties shows the full evolution of plasmasphere density from the narrowing of a sunward plume at the onset of erosion, that begins to corotate into a duskside bulge as activity diminishes, to the outward recovery of the plasmapause over several days. A piecewise empirical model of plasmasphere refilling is composed from profiles of equatorial electron density and the observed correlation between the Kp-index and plasmapause location. The RAM-CPL timescale of refilling mediates the increase in density from plasmatrough to plasmasphere levels matching RBSP measurements during the quiet period after the storm. Density observations of the other geomagnetic events are consistent with reports of a two-stage refilling process.

ABSTRACT LOCAL MODELING OF THE IONOSPHERIC VERTICAL TOTAL ELECTRON CONTENT (VTEC) USING PARTICLE FILTER Aghakarimi, Armin M.Sc., Department of Geodetic and Geographic Information Technologies Supervisor: Prof. Dr. Mahmut Onur Karslioglu September 2012, 98 pages Ionosphere modeling is an important field of current studies because of its influences on the propagation of the electromagnetic signals. Among the various methods of obtaining ionospheric information, Global Positioning System (GPS) is the most prominent one because of extensive stations distributed all over the world. There are several studies in the literature related to the modeling of the ionosphere in terms of Total Electron Content (TEC). However, most of these studies investigate the ionosphere in the global and regional scales. On the other hand, complex dynamic of the ionosphere requires further studies in the local structure of the TEC distribution. In this work, Particle filter has been used for the investigation of local character of the ionosphere VTEC. Besides, standard Kalman filter as an effective method for optimal state estimation is applied to the same data sets to compare the corresponding results with results of Particle filter. The comparison shows that Particle filter indicates better performance than the standard Kalman filter especially during the geomagnetic storm. MATLAB&copy / R2011 software has been used for programing all processes and algorithms of the study.

Saturn’s largest moon, Titan, presents a very interesting subject for study because of its atmosphere’s complex organic chemistry. Processes taking place there might shed some light on the origins of organic compounds on Earth in its early days. The international spacecraft Cassini-Huygens was launched to Saturn in 1997 for a detailed study of the gas giant and its moons, specifically Titan. The Swedish Institute of Space Physics in Uppsala has manufactured the Langmuir probe instrument for the Cassini spacecraft now orbiting Saturn, and is responsible for its operation and data analysis. This project concerns the analysis of Titan’s ionosphere measurements from this instrument, from all “deep” flybys of the moon (<1400km altitude) in the period October 2004 - April 2010. Using the Langmuir Probe analysis tools, the ion flux is derived by compensating for the atmospheric EUV extinction (that varies with the photoelectron current from the probe). The photoelectron current emitted from the probe also gives an artifact in the data that for this project needs to be deducted before analysis. This factor has already been modeled, while the extinction of Titan’s atmosphere has only been taken into account on event basis (not systematically). The EUV corrected ion flux data is then used to derive the ion number density in Titan’s atmosphere, by setting up an average ion mass altitude distribution (using the Ion Neutral Mass Spectrometer results for comparison) and deriving the spacecraft speed along the Cassini spacecraft trajectory through Titan’s ionosphere. The ion number density results proved to correlate very well with the theoretical ionospheric profiles on the day side of Titan (see graphical representation in the Results section). On the night side, a perturbation of the ion flux data was discovered by comparison with Ion Neutral Mass Spectrometer data, supporting earlier measurements of negative ions reported by Coates et al 2009. The project was carried out at the Swedish Institute of Space Physics (Institutet för Rymdfysik, IRF) in Uppsala. / Saturnus största måne Titan är ett väldigt intressant forskningsobjekt på grund av dess atmosfärs komplexa organiska kemi. Processer som pågår i Titans täta atmosfär kan hjälpa oss att förstå ursprunget till organiska föreningar på Jorden i dess unga ålder. Den internationella rymdsonden Cassini-Huygens blev uppskjuten mot Saturnus 1997, för att i detalj undersöka gasjätten och dess månar, speciellt Titan. Institutet för Rymdfysik (IRF) i Uppsala är ansvariga för operation och dataanalys av Langmuirsonden ombord Cassini som ligger i omloppsbanan kring Saturnus sedan 2004. Detta projekt omfattar analys av Langmuirsondens mätningar av Titans jonosfär från alla ”djupa” förbiflygningar av månen under perioden oktober 2004 – april 2010. Med hjälp av analysverktygen för Langmuirsonden, tas jonflödet fram efter kompensation för den atmosfäriska EUV extinktionen som ger upphov till fotoelektronströmmen från sonden. Fotoelektronströmmen som utsänds från proben ger en artefakt i data och måste (för detta projekt) korrigeras före analysen. Denna faktor är redan bestämd, men extinktionen av Titans atmosfär har endast korrigerats för i enstaka fall. Det korrigerade datat används för att få fram jondensiteten i Titans atmosfär genom att en genomsnittlig jonmass/höjd fördelning antas (jämförs med resultat från INMS-instrumentet) och kombineras med den beräknade hastighet som Cassini håller i banan genom jonosfären. Projektet utfördes vid Institutet för Rymdfysik, Uppsala.

From a HF propagation point of view, the ionospheric layers act as partially conducting media (plasma) in which a transmitted radio wave can reflect upon.A way of determining whether a radio wave with a given frequency will reflect from the ionosphere or completely penetrate is to utilize special radar instruments know as ionosondes or chirp sounders. The technique is widely used by amateur enthusiasts and military radio users for monitoring available radio channel links between two remote locations and can often serve as a base for HF radio prognoses.The objective of this Bachelor’s Thesis was to explore, implement and test a single channel receiver for monitoring ionospheric sounders. The implementation is based on Software Defined Radio (SDR) technology and relies on the GNU Chirp Sounder (gcs) open source script program.

This work studies the current collected by the spherical Langmuir probes to be mounted on the ESA Swarm satellites in order to quantify deviations from idealized cases caused by non-ideal probe geometry. The finite-element particle-in-cell code SPIS is used to model the current collection of a realistic probe, including the support structures, for two ionospheric plasma conditions with and without drift velocity. SPIS simulations are verified by comparing simulations of an ideal sphere at rest to previous numerical results by Laframboise parametrized to sufficient accuracy. It is found that for probe potentials much above the equivalent electron temperature, the deviations from ideal geometry decrease the current by up to 25 % compared to the ideal sphere case and thus must be corrected if data from this part of the probe curve has to be used for plasma density derivations. In comparison to the non-drifting case, including a plasma ram flow increases the current for probe potentials around and below the equivalent ion energy, as the contribution of the ions to the shielding is reduced by their high flow energy.

published_or_final_version / Physics / Master / Master of Philosophy