Dissertations / Theses on the topic 'Scintillation-Ionospheric'
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Jiao, Yu. "High Latitude Ionospheric Scintillation Characterization." Miami University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=miami1376909513.
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Ho, Yih Hwa. "Mitigation of ionospheric scintillation effects on GNSS." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539702.
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Moraes, Alison de Oliveira. "Advances in statistical modeling of ionospheric scintillation." Instituto Tecnológico de Aeronáutica, 2013. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=2240.
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Ionospheric scintillation is a phenomenon that occurs daily, especially around the equatorial region, during the summer solstice after the sunset, affecting radio signals that propagate through the ionosphere. Depending on the temporal and spatial situation, ionospheric scintillation can represent a problem in the availability and precision of the Global Navigation Satellite Systems (GNSS). This work is concerned with the statistical modeling and evaluation of the impact of amplitude scintillation on the performance of Global Positioning System (GPS) receivers. In this work the use of ?-? model is proposed to represent the scintillation phenomenon affecting GPS receiver performance. The use of ?-? is also extended for second order statistics. Such a model is compared to a set of experimental data obtained in São José dos Campos, near the peak of the Equatorial Anomaly, during high solar fux conditions, between the months of December 2001 and January 2002. The results obtained with the proposed ?-? model fitted quite well with the experimental data and performed better than two of the widely used models, namely Nakagami-m and Rice. The proposed model requires the estimation of two parameters, instead of a single one used by the models of Nakagami-m and Rice. To facilitate its use, for the situations in which no set of experimental data is available, this work presents parameterized equations for calculating the two parameters required by the ?-? model. Based upon the fact that the proposed model performs better than the one proposed by Nakagami-m, the present investigation derives a model to estimate the carrier and code tracking loop errors on GPS receivers. Such a model not only performed better than Nakagami';s, but also is valid for a wider range of scintillation.
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Burston, Robert. "Investigating ionospheric scintillation mechanisms via theory and experimentation." Thesis, University of Bath, 2009. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516941.
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This thesis aims to answer the question, “What physical process dominates the formation of plasma irregularities, capable of directly or indirectly causing GPS L1 band scintillation, in polar cap plasma patches during magnetic storm conditions?.” A novel modelling technique utilising an ionospheric imaging algorithm is developed and used to elucidate the relative importance of the two most commonly discussed processes. These are the Gradient Drift Instability (GDI) and turbulence induced by electric field mapping to the ionosphere from the magnetosphere. The results show that in magnetic storm conditions, at times the GDI process is dominant, but that at other times turbulence may be as significant as the GDI in determining how the plasma within a polar cap patch behaves, possibly more so. This in turn suggests that further study of the turbulence process is necessary in order to fully understand how big a role it plays in causing GPS L1 band scintillation in the polar cap. The success of the modelling technique developed here shows the utility of ionospheric imaging as a tool for understanding physical problems of the ionosphere; efforts to improve it and to apply it in other contexts would be worthwhile.
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Knight, Mark Frederick. "Ionospheric scintillation effects on global positioning system receivers." Title page, contents and abstract only, 2000. http://web4.library.adelaide.edu.au/theses/09PH/09phk698.pdf.
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Boryczko, Marta, and Tomasz Dziendziel. "Optimisation Of Ionospheric Scintillation Model Used In Radio Occultation." Thesis, Blekinge Tekniska Högskola, Institutionen för tillämpad signalbehandling, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-11915.
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This thesis is executed in cooperation with RUAG Space AB, which specializes in highly reliable on-board satellite equipment. The thesis focuses on the effect, which disturbs the amplitude and phase of a Global Positioning System (GPS) signal, called scintillation effect. It has a substantial impact on a GPS signal, during Radio Occultation (RO). RO is a method of analysis of a refracted signal which passes through the atmosphere. RO can be used for measuring climate change and for weather forecasting. By retrieving the bending angle of a GPS signal, three basic parameters of the Earth’s atmosphere can be obtained at different heights: temperature, pressure and humidity. As the scintillation effect causes prominent errors in the bending angle calculations, it is crucial to provide possibly the most precise mathematical model, which allows to conceive proper ionospheric corrections. In this thesis, the model using Rytov approach is implemented and optimised with different optimisation functions. It is shown that the scintillation model can be optimized, which may contribute to a more accurate retrieval of the atmospheric profiles.
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Atilaw, Tsige Yared. "Characterization of the Multipath Environment of Ionospheric Scintillation Receivers." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/16475.
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Includes bibliographical referencesGlobal Navigation Satellite Systems (GNSS) are used to provide information on position, time and velocity all over the world at any time of the day. Currently there are four operational GNSS and one of them is GPS (Global Positioning System) that is developed and maintained by U.S Department of Defence (DoD), which is widely used and accessible all over the world. The accuracy of the output or even the availability of the navigation system depends on current space weather conditions, which can cause random fluctuations of the phase and amplitude of the received signal, called scintillation. Interference of GNSS signals that are reflected and refracted from stationary objects on the ground, with signals that travel along a direct path via the ionosphere to the antenna, cause errors in the measured amplitude and phase. These errors are known as multipath errors and can lead to cycle slip and loss of lock on the satellite or degradation in the accuracy of position determination. High elevation cut off angles used for filtering GNSS signals, usually 15-30°, can reduce non-ionospheric interference due to multipath signals coming from the horizon. Since a fixed-elevation threshold does not take into consideration the surrounding physical environment of each GPS station, it can result in a significant loss of valuable data. Alternatively, if the fixed-elevation threshold is not high enough we run the risk of including multipath data in the analysis. In this project we characterized the multipath environment of the GPS Ionospheric Scintillation and TEC (Total Electron Content) Monitor (GISTM) receivers installed by SANSA (South African National Space Agency) at Gough Island (40:34oS and 9:88° W), Marion Island (46:87° S and 37:86° E), Hermanus (34:42° S and19:22° E) and SANAE IV (71:73° S and 2:2° W) by plotting azimuth-elevation maps of scintillation indices averaged over one year. The azimuth-elevation maps were used to identify objects that regularly scatter signals and cause high scintillation resulting from multipath effects. After identifying the multipath area from the azimuth-elevation map, an azimuth-dependent elevation threshold was developed using the MATLAB curve fitting tool. Using this method we are able to reduce the multi-path errors without losing important data. Using the azimuth-dependent elevation threshold typically gives 5 to 28% more useful data than using a 20° fixed-elevation threshold.
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Kumagai, Hiroshi. "Mid-latitude ionospheric irregularities deduced from spacedreceiver scintillation measurements." Kyoto University, 1988. http://hdl.handle.net/2433/162220.
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Romano, Vincenzo. "Ionospheric scintillation effects on GNSS : monitoring and data treatment development." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33909/.
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The increasing importance of satellite navigation technologies in modern society implies that a deeper knowledge and a reliable monitoring of the scintillation phenomena are essential to warn and forecast information to the end users and system designers. In fact, warnings, alerts and forecasting of ionospheric conditions may wisely tune the development of GNSS-based services to obtain the necessary levels of accuracy, integrity, and immediacy for reliable life-critical applications. The PhD research project is within the framework of the longstanding NGI-INGV collaboration, increasingly consolidated in the framework of many international projects. NGI pioneered GPS ionospheric scintillation monitoring in Northern Europe with GISTM (GPS ionospheric scintillation and TEC monitor, Van Dierendonck et al., 1993; Van Dierendonck, 2001) receivers. Between June 2001 and December 2003, four units were installed in the UK and Norway mainland, covering the geographic latitudes from 53° N to 70° N. Data was stored and analysed, focusing on statistical analyses and impact for GNSS users (Rodrigues et al., 2004, Aquino et al., 2005a, Aquino et al., 2005b). These units were decommissioned in 2004 and, then, re-deployed together with additional new receivers, in UK, Norway, Italy and Cyprus. An additional station was deployed by the NGI in Dourbes, Belgium (in collaboration with the Royal Meteorological Institute of Belgium) between 2006 and 2011. INGV leads the ISACCO (Ionospheric Scintillation Arctic Campaign Coordinated Observations) project in the Arctic, started in 2003, in which frame the management of three GISTM receivers in Svalbard (De Franceschi et al., 2006) and another two at European mid-latitudes, Chania (Greece) and Lampedusa (Italy), is currently undertaken. The PhD research project contributed to the reinforcement of the NGI-INGV GISTM network developing monitoring, data management and quality tools. Such activities have supported the continuity and the control of the receiving stations, as well as the access and the preservation of the both real-time and historical data acquired. In fact, a robust, continuous data acquisition and a wise management of the GISTM network are of paramount importance for Space Weather applications, as they are the basis on which reliable forecasting and now-casting of possible effects on technological systems lean. Moreover, the possibility to use the data for scientific and applicative purposes depends upon well-established data quality procedures and upon a detailed knowledge of the sites in which each receiver comprising the network are deployed. Starting from these considerations, and in the framework of the aforementioned collaborative context, the PhD work aimed at improving the monitoring techniques and developing novel data processing to improve the data quality. Scintillation measurements are contaminated by multiple scattering encountered by the GNSS signal due to buildings, trees, etc. Such multipath sources need to be identified to keep the quality of the scintillation and TEC data as higher as possible. This can be achieved by removing these sources of errors or mitigating their effects by filtering the data. A novel station characterization technique has been introduced, developed and discussed in this thesis. The results demonstrated that this is a promising method to improve the quality of data (Romano et. al 2013). The results obtained so far motivated the development of the data filtering procedures. The filtering was aimed at filtering-out spurious, noisy data based on general assumptions about statistical data analysis (outlier analysis), thus efficiently removing multipath affected measurements and reducing the data loss with respect to applying a fixed elevation angle cut-off threshold. This is particularly important in case of not well covered regions (e.g. forests, deserts, oceans, etc.), as the field of view spanned by each antenna is optimized. During the PhD activities, the filtering technique has been also tested and validated against real and simulated data. To show how the development of the filtering method is able to efficiently clean multipath and signal degradation from GNSS data, it was applied in two different cases: - First, it was applied to the data published in a climatological study (Alfonsi et al. 2011), carried out with the NGI-INGV GISTM network at high-latitudes. Each station was characterized using the station characterization method, and then the data were filtered using the filtering method. Then, the new climatological maps were generated and compared to the original ones. The percentage of the filtered-out data obtained by applying the standard threshold of 20° on the elevation angle and the filtering technique for each station demonstrated how the latter is able to meaningfully reduce the data loss. The filtering extends the field of view of the network and, then, improves the capability of investigating the dynamics of the ionosphere over larger areas. - Second, the data used in this application were acquired by the CIGALA/CALIBRA network of PolaRxS receivers during the whole year of 2012. The elevation angle cut-off significantly reduced the capability of the network to depict the ionosphere northward of the geomagnetic equator and above the Atlantic Ocean, east of Brazil. This approach limited the data loss to 10-20%, while the traditional cut off of 15°-30° on the elevation angle led to losses of 35-45%. This method not only optimized the capability of GNSS networks, but also helped in planning the installation of additional new receivers aiming to enlarge network coverage in the framework of the CALIBRA project. The enlarged field of view made it possible to identify the increased occurrence of scintillation along the northern crest of the Equatorial Ionospheric Anomaly (EIA). To summarize and to introduce the reader into this thesis, specific issues here addressed are: - Development of software procedures and hardware designs to optimize the station configurations of the existing measurement network of GISTM (GPS Ionospheric Scintillation and TEC Monitor). - Development of techniques for remote, automatic instrument control and setting. - Development of data management tools to achieve quasi real-time data accessibility. - Development of data analysis methods to assess station characterization. - Development of techniques to perform data quality filtering. - Perform acquisition of experimental and simulation data. - Support scientific investigations through the high quality of the NGI-INGV network data.
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Kinrade, Joe. "Ionospheric imaging and scintillation monitoring in the Antarctic and Arctic." Thesis, University of Bath, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619217.
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Electron density irregularities influence Global Navigation Satellite System (GNSS) signals, manifesting as ionospheric scintillation. Scintillation poses a service risk to safety-critical GNSS applications at high latitudes. It is difficult to predict, as ionospheric instability processes are not yet fully characterised. This research combines the fields of ionospheric imaging and scintillation monitoring, to investigate the causes of scintillation in the Antarctic and Arctic. Results revealed a plasma patch structure above Antarctica, in response to the impact of a solar wind shock front. Measurements from a network of Global Positioning System scintillation receivers across the continent revealed moderate levels of phase scintillation associated with Total Electron Content (TEC) gradients at the patch break-off point. Scintillation was also driven by solar particle precipitation at E and F region altitudes, verified with in situ spectrometers on polar-orbiting satellites. The current receiver coverage in the region provided the Multi-Instrument Data Analysis Software (MIDAS) tomography tool with sufficient data to track the lifetime of the plasma patch without a convection model. A second experiment was performed at the South Pole, using a collocated GPS scintillation receiver and auroral imager. This allowed simultaneous line-of-sight tracking of GPS signals through the optical auroral emissions. Results showed the first statistical evidence that auroral emissions can be used a proxy for ionospheric irregularities causing GPS scintillation. The relationship was strongest during the presence of discrete auroral arcs. Correlation levels of up to 74% were found over periods of 2-3 hours. The use of multiple emission wavelengths provided basic altitude discrimination. Current capability of ionospheric TEC mapping in the Arctic was tested, where GPS receiver distribution is extensive compared to present Antarctic coverage. Analysis of the ionosphere’s response to a storm event revealed a sequential picture of polar cap patch activity, without the aid of plasma convection modelling. The electron density enhancements of the auroral oval were imaged in completeness for the first time using GPS tomography. Reconstructions were verified using ultraviolet auroral imagery from polar-orbit satellites, and vertical profiles from an incoherent scatter radar.
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Olivarez, Nathan. "Mitigating the Effects of Ionospheric Scintillation on GPS Carrier Recovery." Digital WPI, 2013. https://digitalcommons.wpi.edu/etd-theses/245.
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Ionospheric scintillation is a phenomenon caused by varying concentrations of charged particles in the upper atmosphere that induces deep fades and rapid phase rotations in satellite signals, including GPS. During periods of scintillation, carrier tracking loops often lose lock on the signal because the rapid phase rotations generate cycle slips in the PLL. One solution to mitigating this problem is by employing decision-directed carrier recovery algorithms that achieve data wipe-off using differential bit detection techniques. Other techniques involve PLLs with variable bandwidth and variable integration times. Since nearly 60% of the GPS signal repeats between frames, this thesis explores PLLs utilizing variable integration times and decision-directed algorithms that exploit the repeating data as a training sequence to aid in phase error estimation. Experiments conducted using a GPS signal generator, software radio, and MATLAB scintillation testbed compare the bit error rate of each of the receiver models. Training-based methods utilizing variable integration times show significant reductions in the likelihood of total loss of lock.
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Praveen, Vikram. "Event Driven GPS Data Collection System for Studying Ionospheric Scintillation." Miami University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=miami1323894410.
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Carroll, Mark Joseph. "Advanced GPS Receiver Algorithms for Assured Navigation During Ionospheric Scintillation." Miami University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=miami1399602874.
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Brosie, Kayla Nicole. "Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/78710.
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A full solar eclipse is going to be visible from a range of states in the contiguous United States on August 21, 2017. Since the atmosphere of the Earth is charged by the sun, the blocking of the sunlight by the moon may cause short term changes to the atmosphere, such as density and temperature alterations. There are many ways to measure these changes, one of these being ionospheric scintillation. Ionospheric scintillation is rapid amplitude and phase fluctuations of signals passing through the ionosphere caused by electron density irregularities in the ionosphere. At mid-latitudes, scintillation is not as common of an occurrence as it is in equatorial or high-altitude regions. One of the theories that this paper looks into is the possibility of the solar eclipse producing an instability in the ionosphere that will cause the mid-latitude region to experience scintillations that would not normally be present. Instabilities that could produce scintillation are reviewed and altered further to model similar conditions to those that might occur during the solar eclipse. From this, the satellites that are being used are discuses, as is hardware and software tools were developed to record the scintillation measurements. Although this work was accomplished before the eclipse occurred, measurement tools were developed and verified along with generating a model that predicted if the solar eclipse will produce an instability large enough to cause scintillation for high frequency satellite downlinks.Master of Science
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Locubiche-Serra, Sergi. "Robust Carrier Tracking Techniques for GNSS Receivers affected by Ionospheric Scintillation." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/668304.
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Las tecnologías de posicionamiento por satélite (GNSS, del inglés global navigation satellite systems) se han convertido en una herramienta indispensable en diferentes ámbitos de nuestra sociedad moderna. Algunos ejemplos de aplicaciones son el posicionamiento y la navegación en entornos terrestre, marítimo y aéreo, así como usos destinados a la agricultura, topografía o aplicaciones de sincronización precisa en sistemas de telecomunicaciones o finanzas. El módulo de tracking es una de las etapas centrales para mantener los receptores alineados con los satélites, y hasta ahora se han empleado técnicas de tracking convencionales de fácil implementación que son suficientes para operar en escenarios con unas condiciones de trabajo favorables. Sin embargo, en los últimos años, el éxito de GNSS en entornos a cielo abierto ha propiciado su expansión hacia aplicaciones en escenarios más exigentes, tales como cañones urbanos o interiores. La tendencia es dotar a los terminales móviles (smartphones) de capacidades de posicionamiento en entornos en donde se enfrentan a nuevos retos tecnológicos dados por los problemas de propagación que abundan. En este sentido, el centelleo ionosférico (ionospheric scintillation en inglés) es uno de los problemas que degradan las prestaciones de los receptores, particularmente en zonas ecuatoriales y a altas latitudes. Es un efecto que introduce rápidas variaciones aleatorias en la fase y la potencia de la señal útil, y tiene un efecto perjudicial precisamente en la etapa de tracking del receptor.
El objetivo de esta tesis es diseñar y desarrollar nuevas técnicas para el tracking robusto de señales GNSS afectadas por el efecto de centelleo ionosférico. La propuesta que se presenta está basada en el uso de técnicas de filtrado de Kalman, y las contribuciones principales de esta tesis son tres. En primer lugar se estudia el efecto de centelleo ionosférico y el tracking de la dinámica del receptor a pesar de su presencia. Diseñamos un filtro de Kalman con una formulación híbrida que permite monitorizar ambas contribuciones por separado de manera robusta. Esto surge de realizar un análisis detallado del centelleo ionosférico en el que se concluye que las variaciones de fase se pueden caracterizar a través de procesos autoregresivos, los cuales se pueden tratar mediante el filtro de Kalman de manera natural. En segundo lugar se diseñan técnicas de filtrado de Kalman adaptativas que permiten ajustar su ancho de banda en función de las condiciones de centelleo, las cuales suelen ser variantes en el tiempo en la práctica. Esta parte incluye un detector de presencia de centelleo, un estimador en tiempo real de los parámetros del modelo autoregresivo, y una implementación para lidiar con las atenuaciones no lineales introducidas por el mismo centelleo. El funcionamiento de las técnicas propuestas se valida posteriormente mediante una campaña extensiva de simulaciones utilizando tanto datos sintéticos como datos reales de centelleo ionosférico, y se cuantifica la región de ganancia respecto a las técnicas convencionales. Por último se propone un innovador método para derivar expresiones para la denominada cota Bayesiana de Cramér-Rao (BCRB, del inglés Bayesian Cramér-Rao bound) que permiten caracterizar el comportamiento de los filtros de Kalman de manera cerrada. Esto supone una contribución a la literatura de gran interés práctico para diseñar filtros de Kalman para cualquier tipo de aplicación.Global Navigation Satellite Systems (GNSS) have become an indispensable tool in different areas in our modern society for positioning purposes using radio-frequency ranging signals. Some application examples are the positioning and navigation in ground, maritime and aviation environments, as well as their use in agriculture, surveying and precise timing and synchronization in communication systems and finances. The tracking stage is one of the core tasks within a GNSS receiver to keep aligned with the satellites and, to date, most receivers equip conventional tracking techniques with ease of implementation that suffice to operate in environments with favorable working conditions. However, in the recent years, the success of GNSS in open-sky environments has led to the emergence of applications that expand toward scenarios with harsher conditions, such as urban canyons and soft-indoor environments. The trend is to provide user mobile terminals such as smartphones with positioning capabilities in scenarios where receivers face new technological challenges owing to the abounding propagation impairments. In this sense, the so-called ionospheric scintillation is one of the issues degrading the performance of GNSS receivers, particularly in equatorial regions and at high latitudes. It introduces rapid carrier phase and signal power variations, and has a detrimental effect particularly onto the tracking stage. The objective of this thesis is to design and develop new techniques for the robust tracking of GNSS signals affected by ionospheric scintillation disturbances. The presented approach is based on the use of Kalman filtering techniques, and the main contributions of the thesis are three. First, the analysis of ionospheric scintillation and the tracking of carrier dynamics despite the presence of the former. We design a Kalman filter with a hybrid formulation that allows the robust monitoring of both contributions separately. This arises from carrying out a detailed analysis of ionospheric scintillation which concludes that scintillation phase variations can be characterized through autoregressive processes, and thus be dealt with within the Kalman filter in a natural manner. Second, the design of adaptive Kalman filter-based techniques that allow self-adjusting their loop bandwidth to the actual scintillation conditions, which are rather time-varying in practice. This part includes a scintillation detector, a real-time estimator of the autoregressive model parameters, and an implementation to address the problem of non-linear signal amplitude attenuation introduced by scintillation itself. The goodness of the proposed techniques is later validated by carrying out an extensive simulation campaign using both synthetic data and real scintillation time series, and the outperformance region with respect to conventional tracking techniques is quantified. Third, a novel method for the derivation of expressions for the termed Bayesian Cramér-Rao bound (BCRB), which allow characterizing the behavior of Kalman filters in a closed-form manner, thus becoming a contribution to the literature of practical usefulness to design Kalman filters for any kind of application.
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Xu, Dongyang. "BEIDOU AND GPS DUAL CONSTELLATION VECTOR TRACKING DURING IONOSPHERE SCINTILLATION AT EQUATORIAL REGION." Miami University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=miami1407512226.
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Jerez, Gabriel Oliveira [UNESP]. "Análise da integração GPS/GLONASS para posicionamento sob efeito de cintilação ionosférica." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/150286.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Com o desenvolvimento dos sistemas globais de navegação por satélite as atividades que envolvem posicionamento passaram por uma revolução. Os pioneiros, GLONASS (GLObal NAvigation Satellite System) e GPS (Global Positioning System), são atualmente os principais sistemas, e únicos com constelação completa. A utilização combinada de dados GPS e GLONASS passou por uma perda de interesse no final da década de noventa devido à rápida degradação que o GLONASS sofreu. Porém, em 2001 teve início um plano de restabelecimento do sistema que em 2011 voltou a contar com constelação completa de 24 satélites e cobertura global. O GLONASS passa ainda por um processo de modernização, com novas gerações de satélites sendo desenvolvidas, refinamentos dos sistemas de tempo e referência e novas estações de controle sendo instaladas. Além do uso de dados combinados, outros fatores que influenciam a qualidade do posicionamento são os métodos empregados e os erros aos quais os sinais transmitidos estão sujeitos. Nas metodologias de integração devem constar as diferenças de estrutura dos sistemas, sendo as principais, para este caso, os sistemas de referência, sistemas de tempo e a tecnologia relacionada às frequências. Em relação aos erros, a ionosfera é uma importante fonte, principalmente para usuários de receptores de apenas uma frequência. Ela exige atenção especial, pois além de degradar a acurácia do posicionamento há uma grande dependência entre perdas do sinal e irregularidades ionosféricas, como a cintilação ionosférica. Na presente pesquisa buscou-se analisar as melhorias apresentadas no posicionamento utilizando dados combinados GPS/GLONASS sob efeito de cintilação ionosférica, avaliar a influência da cintilação nos sinais GLONASS e realizar um estudo da estrutura do sistema. Foram realizados três experimentos, relacionados à aplicação do PPP (Posicionamento por Ponto Preciso), do posicionamento relativo estático e do posicionamento em redes (especificamente no conceito de VRS – Virtual Reference Station). Para possibilitar o posicionamento em redes foi adaptada a ferramenta VRS-UNESP, para permitir a geração de bases virtuais com dados GLONASS ou GPS/GLONASS. Para as três metodologias foram selecionadas estações em três regiões do Brasil com comportamentos ionosféricos distintos visando possibilitar também a análise do efeito da cintilação. Para isso foram escolhidas regiões próximas ao equador geomagnético, próximas a área afetada pelo efeito fonte e ao sul do país, onde se tem menor influência da ionosfera. Para o PPP considerando-se todos os casos, independente da configuração, houve melhoria em 92,28% dos dias com o uso de dados GPS e GLONASS. Para o posicionamento relativo os resultados obtidos foram mais irregulares que para o PPP, sendo que a melhoria ocorreu em 69,18% dos casos. Os dados virtuais foram processados de maneira análoga ao experimento com PPP, obtendo melhoria em 100% os casos analisados ao se utilizar dados GPS e GLONASS.
With the development of the Global Navigation Satellite Systems (GNSS) the activities involving positioning passed by a great revolution. Currently, the pioneers, GLONASS (GLObal NAvigation Satellite System) and GPS (Global Positioning System), are the main systems with full constellation. The interest in the combined use of GPS and GLONASS data had a great fall in the late nineties due to the fast degradation of GLONASS. However, in 2001 a restoration plan of the system began and in 2011 GLONASS recovered the full constellation of 24 satellites with global coverage. Furthermore GLONASS is going through a modernization process, with the development of new satellite generations, time and reference systems refinements and new control stations. Besides the use of combined data, other factors that influence the positioning quality are the applied methods and the errors that can affect the transmitted signals. The integration methodologies must consider the differences in the systems structures, the main differences, for this case, are reference and time systems and the technology related to the frequencies. About the errors, the ionosphere is an important source, mainly for users of single frequency receivers. It requires special attention, because besides of degrading the positioning accuracy there is a great dependency between the loss of signal and ionospheric irregularities, as ionospheric scintillation. In this research it was intended to analyze the improvement of the combined use of GPS/GLONASS data at positioning under ionospheric scintillation effect, evaluate the influence of scintillation at GLONASS signals and perform a study about the structure of the system. Three experiments were performed, the first one is related to the application of PPP (Precise Point Positioning), the second one is about static relative positioning and the third one is about network based positioning (specifically in the Virtual Reference Station concept).To enable the network based positioning the software VRS-UNESP was adapted, in order to allow the generation of virtual stations with GLONASS or GPS/GLONASS data. In the three methodologies were selected three regions of Brazil with distinct ionospheric behavior, in order to evaluate the scintillation effect in the positioning. It was selected regions near to the geomagnetic equator, regions near the fountain effect and in the south of the country, where the ionosphere effect is less intense. For the PPP, considering all the configurations adopted, there was improvement with the use of GPS and GLONASS combined data in 92,28% of the days analyzed. For the relative positioning the results obtained were more irregulars than the ones from PPP. In such case it was achieved improvement in 69,18% of the cases with the use of combined data. The virtual data were processed in a procedure similar to the one used in the PPP experiment. It was achieved improvement in 100% of the cases that were used GPS and GLONASS data.
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Silva, Heloísa Alves da [UNESP]. "Avaliação de modelos estocásticos no posicionamento GNSS." Universidade Estadual Paulista (UNESP), 2009. http://hdl.handle.net/11449/86784.
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Atualmente, o GNSS, em especial o GPS, é uma das tecnologias mais utilizadas para realizar posicionamento. Os modelos funcionais relacionados com as observações GNSS são mais conhecidos do que os modelos estocásticos, visto que o desenvolvimento destes últimos é mais complexo. Normalmente, no posicionamento GNSS são utilizados modelos estocásticos numa forma simplificada, com um modelo padrão, o qual assume que todas as medidas das observações GNSS têm a mesma variância e são estatisticamente independentes. Porém, atualmente os modelos estocásticos relacionados ao GNSS vêm sendo pesquisados com maior profundidade, por exemplo, considerando efeitos de cintilação ionosférica. Este efeito pode ser considerado na modelagem estocástica já que atualmente receptores GNSS permitem a extração de parâmetros de cintilação ionosférica. Além dessa, outro tipo de modelagem estocástica pode ser realizada, no caso, trata-se da consideração da variação dos ângulos de elevação dos satélites durante o rastreio dos dados. Sendo assim, nessa pesquisa foram desenvolvidos e analisados esses dois casos de modelagem estocástica, tanto no posicionamento relativo, quanto no absoluto (por ponto). No posicionamento relativo, ao se considerar a modelagem estocástica em função da cintilação ionosférica, os resultados atingiram melhorias em torno de 93,0% em relação à modelagem padrão. No processamento e análise foram utilizados dados GPS coletados no Norte da Europa, os quais estão sob condições de cintilação ionosférica. No posicionamento relativo considerando a modelagem estocástica em função dos ângulos de elevação dos satélites, as melhorias foram em torno de 89,2%. No caso do posicionamento por ponto, as melhorias em relação a modelagem estocástica padrão atingiram valores de aproximadamente 45,1% e 42,1% considerando, respectivamente...
Nowadays, the GNSS, especially the GPS, is one of the most used techniques to accomplish positioning. The functional models related with the GNSS observables are more known than the stochastic models, considering that the development of the last ones is more complex. Usually, they are used in a simplified form, as the standard model, which assumes that all the GNSS observable have the same variance and are statistically independent. However, the stochastic models are being investigated with more property, for example, considering the ionospheric scintillation effects. This effect can be considered in the stochastic modelling since now receivers GNSS allow the extraction of ionospheric scintillation parameters. Besides that, others stochastic modelling can be accomplished, e.g. considering the variation of the satellites elevation angles during the data tracking. Thus, in this dissertation it was investigated the two cases of stochastic modelling cited above, either in the relative or in the absolute positioning... (Complete abstract click electronic access below)
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Vani, Bruno César [UNESP]. "Investigações sobre modelagem, mitigação e predição de cintilação ionosférica na região brasileira." Universidade Estadual Paulista (UNESP), 2018. http://hdl.handle.net/11449/153701.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Cintilações Ionosféricas são rápidas variações na amplitude e/ou fase de um sinal de rádio ao se propagar por irregularidades na densidade de elétrons na ionosfera. Este fenômeno degrada a performance do posicionamento pelo GNSS, uma vez que pode acarretar, dentre outros aspectos, a degradação na acurácia de observáveis e em perdas de sincronismo no receptor. No Brasil, verifica-se a maior suscetibilidade de ocorrência de cintilação algumas horas após o pôr-do-sol, nas épocas do ano compreendidas entre os equinócios de primavera e outono nos anos de alta atividade solar. Redes GNSS de monitoramento de cintilações estão implantadas no território brasileiro, incluindo a rede CIGALA/CALIBRA – a qual é mantida pela FCT/UNESP com o apoio de parceiros nos últimos sete anos. Os dados de monitoramento permitem a realização de diversas pesquisas sobre características e efeitos da cintilação, incluindo as investigações conduzidas neste projeto. Foram investigados aspectos sobre a modelagem da cintilação ionosférica no Brasil, com ênfase na mitigação dos seus efeitos no PPP e na predição de ocorrência de cintilação. No contexto da mitigação, abordagens existentes foram avaliadas e uma nova proposta foi desenvolvida. A abordagem proposta para mitigação consiste em um novo modelo funcional, novo modelo estocástico e uma estratégia para minimizar os efeitos de perdas de sincronismo. A abordagem proposta foi testada com o suporte do software científico RT-PPP e os resultados obtidos foram promissores, incluindo casos de recuperação da acurácia esperada do PPP, mesmo sob influência de cintilação forte. No contexto da predição, uma integração de bases de dados de monitoramento oriundos de três redes (CIGALA/CALIBRA, ICEA e LISN) permitiu o desenvolvimento de um modelo preditivo (guiado por dados) baseado em redes neurais artificiais. A rede neural é treinada para obter uma estimativa das localidades e horários onde a cintilação é esperada em uma determinada noite, com base em dados de monitoramento obtidos em noites anteriores. Dados de monitoramento de diferentes regiões coletados no começo da mesma noite (logo após o pôr-do-sol) também são utilizados com o objetivo de inferir padrões acerca do surgimento das irregularidades que causam as cintilações e sua relação com o nível de cintilação observado no restante da noite. O modelo permite obter mapas de cintilação preditos com antecedência de uma a quatro horas, os quais são acompanhados de estimativas de qualidade das predições. Em resumo, este projeto apresenta contribuições com potencial para trazer benefícios ao cenário científico-tecnológico nacional. Além disso, os dados de monitoramento da base de dados integrada foram disponibilizados pela internet à comunidade através do software científico ISMR Query Tool, proporcionando suporte à realização de pesquisas adicionais em diversas instituições do Brasil e do mundo.
Ionospheric scintillations are rapid variation in amplitude and/or phase of a radio signal as it propagates through irregularities on electron density in the ionosphere. Such phenomenon degrades the performance of GNSS positioning, because it may cause accuracy degradation on observables and losses of lock, among other aspects. In Brazil, there is more susceptibility to occurrence of scintillations after sunset time between the spring and autumn equinoxes of years with high solar activity. Monitoring networks based on GNSS receivers are deployed over the Brazilian territory such as the CIGALA/CALIBRA network, managed by FCT/UNESP (with support from partners) in the last seven years. Monitoring data allows to develop several research regarding the scintillation effects, as in this thesis. Aspects regarding the modeling of ionospheric scintillation effects in Brazil were investigated, with emphasis on the mitigation of these effects on PPP and predictions of scintillation occurence. In the field of mitigation, existing approaches were investigated and a new one was proposed. The new approach for mitigation relies in both new functional and stochastic models for PPP, as well as a strategy to model effects of losses of lock. The proposed approach was tested with the scientific software RT-PPP and the achieved results were promising, including cases in which the expected accuracy for the PPP was recovered. In the field of the predictions, a database integration was conducted with data from three different networks (CIGALA/CALIBRA, ICEA e LISN). The integration allowed the development of a data-driven predictive model based on artificial neural network. The neural network is trained with data from previous nights. Data from the same night (around the sunset time) is also used to detect patterns regarding the emerging of the irregularities driving scintillation occurrence on the whole night. The model allows to generate maps of predicted scintillation with antecedence from one to four hours. In summary, this thesis shows contributions with potential to create benefits on the scientific and technological scenarios in Brazil. Furthermore, monitoring data from the integrated database was made available to the scientific community via the software ISMR Query Tool, providing support to conduct new research in different institutions from Brazil and the world.
CAPES: 88881.134266/2016-01
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Peng, Yuxiang. "GNSS-based Spacecraft Formation Flying Simulation and Ionospheric Remote Sensing Applications." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/79594.
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The Global Navigation Satellite System (GNSS) is significantly advantageous to absolute and relative navigation for spacecraft formation flying. Ionospheric remote sensing, such as Total Electron Content (TEC) measurements or ionospheric irregularity studies are important potential Low Earth Orbit (LEO) applications. A GNSS-based Hardware-in-the-loop (HIL) simulation testbed for LEO spacecraft formation flying has been developed and evaluated. The testbed infrastructure is composed of GNSS simulators, multi-constellation GNSS receiver(s), the Navigation & Control system and the Systems Tool Kit (STK) visualization system. A reference scenario of two LEO spacecraft is simulated with the initial in-track separation of 1000-m and targeted leader-follower configuration of 100-m along-track offset. Therefore, the feasibility and performance of the testbed have been demonstrated by benchmarking the simulation results with past work.
For ionospheric remote sensing, multi-constellation multi-frequency GNSS receivers are used to develop the GNSS TEC measurement and model evaluation system. GPS, GLONASS, Galileo and Beidou constellations are considered in this work. Multi-constellation GNSS TEC measurements and the GNSS-based HIL simulation testbed were integrated and applied to design a LEO satellite formation flying mission for ionospheric remote sensing. A scenario of observing sporadic E is illustrated and adopted to demonstrate how to apply GNSS-based spacecraft formation flying to study the ionospheric irregularities using the HIL simulation testbed. The entire infrastructure of GNSS-based spacecraft formation flying simulation and ionospheric remote sensing developed at Virginia Tech is capable of supporting future ionospheric remote sensing mission design and validation.Master of Science
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Vermeulen, Annelie. "Identifying Ionospheric Scintillation in the South Atlantic Magnetic Anomaly using motion-affected GPS data from a ship-based receiver." Master's thesis, Faculty of Engineering and the Built Environment, 2019. http://hdl.handle.net/11427/31337.
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his dissertation serves to report on the novel use of a geodetic-grade, dual-frequency Global Positioning System (GPS) Ionospheric Scintillation and Total Electron Content Monitor (GISTM), in an attempt to identify instances of ionospheric scintillation over the South Atlantic Magnetic Anomaly (SAMA) while located aboard the moving polar research vessel SA Agulhas II. The SAMA is a region in the South Atlantic Ocean where the Earth’s magnetic field is weakest in relation to other regions at comparable latitudes, resulting in the precipitation of high-energy particles into the ionosphere during geomagnetic storms. Ionospheric scintillations are rapid fluctuations in the phase and amplitude of trans-ionospheric radio signals resulting from electron density variations along the ray path. As a result, spacebased navigation systems can encounter increased errors in position accuracy or complete loss of lock. These are risk factors for modern aircraft and ocean vessels which rely on access to accurate Position, Navigation and Timing (PNT) services to operate safely. In this research, only the radio signals from GPS satellites are specifically used to measure these fluctuations. Traditional scintillation measurements are done using dedicated dual-frequency GPS receivers at fixed terrestrial locations. Most of the SAMA lies beyond the reach of the land-based sensors. The South African National Space Agency (SANSA) operates several GISTM stations in Southern Africa, at Marion Island, Gough Island, and the SANAE-IV base in Antarctica. The NovAtel GSV4004B GPS Ionospheric Scintillation and Total Electron Content Monitor (GISTM) installed on board the SA Agulhas II in 2012 has enabled for the first time the terrestrial measurement of scintillation from within the SAMA region. In this project, the amplitude scintillation (S4) and phase scintillation (σφ) indices from 50 Hz L1 GPS signals recorded during the 2014 and 2015 voyages of the SA Agulhas II were analysed for the first time. The scintillation effects are characterised in terms of position and motion data, carrierto-noise-density ratio, number of satellites, and satellite lock time. The goal is to develop an understanding of the effect of motion on the quality of data recorded by the receiver. The roll angle thresholds for the SA Agulhas II are calculated and it is shown that multipath errors are unlikely to be experienced. Significant data challenges were identified stemming from the incorrect setup of the SA Agulhas II GISTM. Data from elevations below 10° were missing because of hard-coded limitations within the GISTM on-board software. The data underwent significant reprocessing before being used. Comparisons were done in-harbour and out at sea with data from the nearest stationary GISTM receivers. It was shown that the movement of the receiver induces significant noise in the data. The noise levels are proportional to the velocity of the ship. An attempt to filter out the noise was unsuccessful. The motion-induced noise in the ship data masked the presence of any potential scintillations. With the ability to detect scintillation compromised, it was decided that a comparison with a land-based receiver within the SAMA would be necessary. Only one identical GISTM receiver met these requirements, located on Gough Island, at 40°20’ 58.90" S, 9°52’ 49.35" W. Data was isolated from both the SA Agulhas II GISTM and Gough Island GISTM for a period where the separation between the two receiver locations was less than 100 km. The Symmetric-Horizontal disturbance index (SYM-H) was used to identify geomagnetic storm conditions. GPS visibility maps were used to identify any potential signal obstructions. No correlation could be seen between position error and the number of satellites locked due to the high number of GPS satellites available at all times. It was discovered that the high noise levels had no effect on the position accuracy of the moving receiver, but that rapid changes in the instantaneous velocity coincided with peaks in the position error. No scintillation events were identified using the SA Agulhas II GISTM as a result of masking by the noise, however, the Gough Island GISTM data showed that no scintillation events occurred during the period in question anyway. Wind was identified as a potential contributing factor to the motion noise effect. This study provided justification for the purchase and installation of a newly developed motion-compensated GISTM receiver on board the SA Agulhas II, running off the same antenna and thus the same received signals. These data sets can be used for a direct receiver comparison in future work.
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Silva, Heloísa Alves da. "Avaliação de modelos estocásticos no posicionamento GNSS /." Presidente Prudente : [s.n.], 2009. http://hdl.handle.net/11449/86784.
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Resumo: Atualmente, o GNSS, em especial o GPS, é uma das tecnologias mais utilizadas para realizar posicionamento. Os modelos funcionais relacionados com as observações GNSS são mais conhecidos do que os modelos estocásticos, visto que o desenvolvimento destes últimos é mais complexo. Normalmente, no posicionamento GNSS são utilizados modelos estocásticos numa forma simplificada, com um modelo padrão, o qual assume que todas as medidas das observações GNSS têm a mesma variância e são estatisticamente independentes. Porém, atualmente os modelos estocásticos relacionados ao GNSS vêm sendo pesquisados com maior profundidade, por exemplo, considerando efeitos de cintilação ionosférica. Este efeito pode ser considerado na modelagem estocástica já que atualmente receptores GNSS permitem a extração de parâmetros de cintilação ionosférica. Além dessa, outro tipo de modelagem estocástica pode ser realizada, no caso, trata-se da consideração da variação dos ângulos de elevação dos satélites durante o rastreio dos dados. Sendo assim, nessa pesquisa foram desenvolvidos e analisados esses dois casos de modelagem estocástica, tanto no posicionamento relativo, quanto no absoluto (por ponto). No posicionamento relativo, ao se considerar a modelagem estocástica em função da cintilação ionosférica, os resultados atingiram melhorias em torno de 93,0% em relação à modelagem padrão. No processamento e análise foram utilizados dados GPS coletados no Norte da Europa, os quais estão sob condições de cintilação ionosférica. No posicionamento relativo considerando a modelagem estocástica em função dos ângulos de elevação dos satélites, as melhorias foram em torno de 89,2%. No caso do posicionamento por ponto, as melhorias em relação a modelagem estocástica padrão atingiram valores de aproximadamente 45,1% e 42,1% considerando, respectivamente... (Resumo completo, clicar acesso eletrônico abaixo)Abstract: Nowadays, the GNSS, especially the GPS, is one of the most used techniques to accomplish positioning. The functional models related with the GNSS observables are more known than the stochastic models, considering that the development of the last ones is more complex. Usually, they are used in a simplified form, as the standard model, which assumes that all the GNSS observable have the same variance and are statistically independent. However, the stochastic models are being investigated with more property, for example, considering the ionospheric scintillation effects. This effect can be considered in the stochastic modelling since now receivers GNSS allow the extraction of ionospheric scintillation parameters. Besides that, others stochastic modelling can be accomplished, e.g. considering the variation of the satellites elevation angles during the data tracking. Thus, in this dissertation it was investigated the two cases of stochastic modelling cited above, either in the relative or in the absolute positioning... (Complete abstract click electronic access below)
Orientador: Paulo de Oliveira Camargo
Coorientador: João Francisco Galera Monico
Banca: Mauricio Alfredo Gende
Banca: Silvio Jacks dos Anjos Garnés
Mestre
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Caldeira, Mayara Cobacho Ortega [UNESP]. "Análise do impacto do efeito ionosférico e cintilação ionosférica no Posicionamento Baseado em Redes e Por Ponto." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/144291.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Visando usufruir do potencial dos sistemas de posicionamento global existentes, novos métodos de posicionamento têm surgido e outros vêm sendo aprimorados. Uma grande tendência nos últimos anos tem sido o uso de redes de estações GNSS de referência. Mas, tanto no uso de redes como nos demais métodos, um fator importante para melhorar a qualidade do posicionamento está relacionado com a modelagem atmosférica. Especial atenção deve ser dada aos erros que ocorrem devido à ionosfera, pois ela se tornou a principal fonte de erro no posicionamento GNSS, após desativação da técnica SA. Este erro é diretamente proporcional ao Conteúdo Total de Elétrons (TEC) e inversamente proporcional ao quadrado da frequência do sinal. O TEC e, consequentemente, o erro ionosférico variam no tempo e no espaço, e sofrem diversas influências, como: ciclo solar, época do ano, hora local, localização geográfica, atividade geomagnética, entre outros. Atualmente, o os erros proporcionados pela ionosfera podem ter seus efeitos minimizados a partir de arquivos IONEX ou por meio de modelagem ionosférica. Portanto, nesta pesquisa, foram utilizados dados das estações da RBMC em diferentes regiões do Brasil no período de baixa e alta densidade de elétrons do pico solar 24 para avaliar o desempenho dos mapas ionosféricos, no posicionamento baseado em redes, disponibilizados por diversos centros (CODE, ESA, JPL, UPC e IGS), bem como os fornecidos pelo projeto MIMOSA, e também os modelos de Grade (AGUIAR, 2010) e estimativa de TEC. Para tal fim, foi adotado um sistema computacional desenvolvido na FCT/UNESP, denominado VRS-Unesp, que emprega o conceito de Estação Virtual. De acordo com os resultados obtidos, nota-se que não há um único mapa fornecido pelos centros de análise do IGS que melhor se enquadra a realidade brasileira, além disso, o desempenho do mapa depende das condições ionosféricas e, principalmente, da localização da estação. Além disso, verificou-se que a acurácia obtida pelo IONEX do projeto MIMOSA, pelo modelo de grade e de Estimativa do TEC que utilizam dados regionais e possuem maior resolução espacial e temporal, foram os que apresentaram os melhores resultados. Por fim foi avaliada a correlação entre a acurácia do posicionamento por ponto e o índice de cintilação S4, já que a ionosfera pode não apenas degradar a acurácia do posicionamento GNSS como reduzir sua disponibilidade, pois existe uma alta dependência entre perdas do sinal e irregularidades ionosféricas. Como resultado, considerando a análise de espaço-frequência em relação ao tempo pelo método coerência wavelets para avaliação da correlação da série, nota-se uma correlação no périodo do equinócio superior a 70%.
In order to take advantage from global positioning systems, new positioning methods have emerged and others have been improved. An important tendency in recent years has been the use of GNSS reference stations networks. But, using networks or other positioning methods an important factor to improve the positioning quality is related to atmospheric modeling. Special attention should be given to errors that occur due to ionosphere, it became the largest error source in GNSS positioning after disabling SA technique. Ionosphere error depends on signal frequency and Total Electron Content (TEC) in the ionospheric layer. TEC and consequently the ionospheric error varies regularly in time and space and they are affected by different sources like: sunspot number (solar cycle), season, local time, geographic position, geomagnetic activity, and others. Currently, the errors provided by the ionosphere can be minimized using IONEX files or models. Therefore, in this research, the RBMC stations data were used in different regions of Brazil in the period of low and high electron density of the cycle solar 24 to evaluate the performance of the ionospheric maps, in network-based positioning, available from several centers, as CODE , ESA, JPL, UPC and IGS, as well as those provided by the MIMOSA project, and also the Grade Models (AGUIAR, 2010) and TEC Estimates. For this, a computer system developed in FCT / UNESP has been adopted, RSV-Unesp that uses the concept of Virtual Station. According to the results, we note that there is not single map of IGS analysis centers that best fits the Brazilian reality, moreover, the map performance depends on the ionospheric conditions and, primarily, the station location. Moreover, it was found that the accuracy obtained by IONEX the MIMOSA project, the Grade Model and TEC estimation using regional data and have higher spatial and temporal resolution, showed the best results. Finally we evaluated the correlation between the accuracy of point positioning and scintillation index S4, since the ionosphere can not only degrade the accuracy of GNSS positioning as well as reduce its availability, because there is a high dependency between signal loss and ionospheric irregularities. As result, considering the space-frequency analysis with respect to time by the wavelet coherence method for evaluation of the correlation of the series, there is a correlation in the period of higher equinox to 70%.
FAPESP: 2014/03858-9
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Galmiche, Aurélien. "Modélisation de la scintillation ionosphérique en zone équatoriale : application à l'inversion des signaux GNSS pour la caractérisation de la turbulence." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30053.
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L'ionosphère est un milieu ionisé dont les variations spatiales et temporelles de densité électronique perturbent la propagation des ondes électromagnétiques. En particulier, la nature turbulente du plasma ionosphérique conduit à des fluctuations rapides de l'amplitude et de la phase des signaux radioélectriques : c'est le phénomène de scintillation ionosphérique dont les effets sont particulièrement sensibles aux latitudes équatoriales sur les systèmes ayant un besoin accru de précision, de disponibilité et d'intégrité de la mesure, tel que les systèmes de localisation GNSS. L'objectif de cette thèse est justement d'exploiter de façon opportune les effets de la scintillation ionosphérique sur le signal pour proposer un sondage des caractéristiques de l'ionosphère turbulente par inversion des mesures GNSS. Dans un premier temps, les spécificités de la dynamique du plasma ionosphérique équatorial responsable des effets de scintillation sont rappelées. Ensuite, à partir d'une description spectrale des fluctuations turbulentes de densité électronique, une modélisation analytique puis numérique de la propagation transionosphérique sont proposées. Celles-ci sont complétées par la prise en compte du récepteur GNSS, finalisant la modélisation du problème direct. À ce stade, un algorithme d'inversion original des données GNSS est proposé. Son application intensive à la base de données SAGAIE collectée en Afrique équatoriale démontre alors la capacité de l'approche inverse à restituer divers paramètres descriptifs de la turbulence ionosphériqueThe ionosphere is an ionized medium, into which the spatio-temporal electronic density variations disrupt the electromagnetic waves propagation. The turbulent ionospheric plasma is in particular linked to rapid amplitude and phase fluctuations of the radio electric signals: this is the ionospheric scintillation phenomenon. Especially around the equatorial latitudes, systems needing great accuracy, availability and measurement integrity are particularly sensitive to its effects. This is the case of the positioning systems using the GNSS technology. The aim of this thesis is to exploit insightly the ionospheric scintillation effects on the signal in order to propose a turbulent ionosphere's characteristics sounding through GNSS measurements inversion. At first, the specificities of the ionosphere's plasma dynamics accounting for the scintillation effects are reminded. Then, from a spectral description of the electronic density's turbulent fluctuations, an analytic and a numeric model of the transionospheric propagation are introduced. They are completed by considering the GNSS receiver. This step finalizes the direct problem's modelization. A new GNSS data inversion algorithm is then come up with. Its intensive application to the SAGAIE database (collected in equatorial Africa) shows the invers approach's capacity to return various parameters describing the ionospheric turbulences
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Nguyen, Thai Chinh [Verfasser], Harald [Akademischer Betreuer] Schuh, Mahdi [Akademischer Betreuer] Alizadeh, Harald [Gutachter] Schuh, Mahdi [Gutachter] Alizadeh, and Lung-Chih [Gutachter] Tsai. "Use of the East Asia GPS receiving network to observe ionospheric VTEC variations, scintillation and EIA features during the Solar Cycle 24 / Thai Chinh Nguyen ; Gutachter: Harald Schuh, Mahdi Alizadeh, Lung-Chih Tsai ; Harald Schuh, Mahdi Alizadeh." Berlin : Technische Universität Berlin, 2021. http://d-nb.info/1231908394/34.
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Mohd, Ali Aiffah. "GNSS in aviation : ionospheric threats at low latitudes." Thesis, University of Bath, 2018. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.761026.
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Radio signals propagating through the ionised upper atmosphere (the ionosphere) in low latitude regions of the world can experience amplitude scintillation. This could threaten safety-critical applications of satellite navigation such as aviation. The research presented here studied the effects of amplitude scintillation on a Septentrio PolaRxS geodetic receiver and a Garmin 480 aviation receiver by means of a Spirent GNSS constellation simulator. Different types of fade profiles showed that an abrupt drop in signal strength caused a loss of lock on the signal more often than a profile with a slow, gradual fade. A performance comparison of the two receivers demonstrated that the aviation receiver was more vulnerable than the geodetic receiver. An unexpected loss of lock at a specific fade duration and depth was seen with the Garmin receiver and was not explained. A single fade with a long fade duration was more likely to cause a loss of signal lock compared to rapid multiple fades. Scintillation on signals from low elevation satellites can significantly degrade the precision and integrity of the navigation solution in an aviation receiver; especially if the satellites are within the best geometrical set. RAIM was observed to be no longer available during the critical landing approach phase of the scenario, in the case when all satellites in view were affected by the scintillation-induced signal perturbations. A technique was also developed to simulate L5 scintillation based on real scintillation events of L1, in the absence of real captured data for L5. This was done to enable future investigations on aviation receiver performance when both L1 and L5 frequencies experience scintillation. Analysis indicated that L5 signal can be more vulnerable to the scintillation compared to the L1 signal, which may have important implications for aviation safety.
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Ludwig, Barbosa Vinícius. "Effects of Small-Scale Ionospheric Irregularities on GNSS Radio Occultation Signals : Evaluations Using Multiple Phase Screen Simulator." Licentiate thesis, Blekinge Tekniska Högskola, Institutionen för matematik och naturvetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-18907.
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Radio Occultation (RO) is a remote sensing technique which uses Global Navigation Satellite System (GNSS) signals tracked by a Low-Earth Orbit (LEO) satellite to sound the earth's atmosphere both in low (troposphere, stratosphere) and high (ionosphere) altitudes. GNSS-RO provides global coverage and SI traceable measurements of atmospheric data with high-vertical resolution. Refractivity, dry temperature, pressure and water vapour profiles retrieved from RO measurements have a relevant contribution in Numerical Weather Prediction (NWP) systems and in climate-monitoring. Due to the partial propagation through the ionosphere, a systematic bias is added to the lower atmospheric data product. Most of this contribution is removed by a linear combination of data for two frequencies. In climatology studies, one can apply a second-order correction - so called κ-correction - which relies on a priori information on the conditions in the ionosphere. However, both approaches do not remove high-order terms in the error due to horizontal gradient and earth's geomagnetic fields. The remaining residual ionospheric error (RIE) and its systematic bias in RO atmospheric data is a well-known issue and its mitigation is an open research topic. In this licentiate dissertation, the residual ionospheric error after the standard correction is evaluated with computational simulations using a wave optics propagator (WOP). Multiple Phase Screen (MPS) method is used to simulate occultation events in different ionospheric scenarios, e.g. quiet and disturbed conditions. Electron density profiles (EDP) assumed in simulations are either defined by analytical equations or measurements. The disturbed cases are modelled as small-scale irregularities within F-region in two different ways: as sinusoidal fluctuations; and by using a more complex approach, where the irregularities follow a single-slope power-law that yields moderate to strong scintillation in the signal amplitude. Possible errors in MPS simulations assuming long segment of orbit and ionosphere are also evaluated. The results obtained with the sinusoidal disturbances show minor influence in the RIE after the standard correction, with the major part of the error due to the F-region peak. The implementation of the single-slope power-law is validated and the fluctuations obtained in simulation show good agreement to the ones observed in RO measurements. Finally, an alternative to overcome limitations in MPS simulations considering occultations with long segment of orbit and ionosphere is introduced and validated. The small-scale irregularities modelled in F-region with the power-law can be added in simulations of a large dataset subjected to κ-correction, in order to evaluate the RIE bending angle and the consequences in atmospheric parameters, e.g. temperature.NRPF-3, Rymdstyrelsen, 241/15
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Huang, Peng Rui, and 黃鵬瑞. "Study of ionospheric scintillation by the rytov approximation." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/06363324583318211719.
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Zhang, Ming Sheng, and 張明生. "Simulations of ionospheric scintillation with the phase screen method." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/52631548766461271681.
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Chiu, Ji-Heng, and 丘濟恆. "GPS Ionospheric Amplitude Scintillation Detection Using Support Vector Machine." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/224427.
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碩士國立臺灣海洋大學
通訊與導航工程學系
106
In this thesis, the problem for detecting ionospheric amplitude scintillation is investigated. We solve this problem using a machine-learning algorithm called Support Vector Machine(SVM). Four kinds of training data are tested, including moving average of ionospheric amplitude scintillation index, moving maximum of ionospheric amplitude scintillation index, power spectrum density of moving average of ionospheric amplitude scintillation index transforming with short-time Fourier transform, power spectrum density of signal intensity transforming with short-time Fourier transform. With the above training data in hand, it is shown in this thesis that the proposed method can effectively detect the ionospheric scintillation in the GPS signals. Comparing with conventional mathematical model, support vector machine is more efficient to identify the ionospheric scintillation feature. When applying the kernel trick appropriately, support vector machine has good results in most classification tasks for both linear and non-linear data.
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LIN, WEI-XIANG, and 林煒翔. "MITIGATING THE EFFECTS OF IONOSPHERIC SCINTILLATION ON GPS CARRIER TRACKING LOOP." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/24930146046796592957.
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碩士國立雲林科技大學
電機工程系
103
Global Positioning System (GPS) about Navigation section of daily life, provide assistance to people. Global Navigation Satellite System can be divided into receiver, the Front-end structure of antenna, this paper focuses on carrier phase tracking in the receiver, when the whole phase-locked loop design was bad, or can't to catch up with phase changes, carrier tracking loss of lock would result the required navigation message cannot be obtained. This article will introduce study of ionospheric scintillation effects. A library of empirical equatorial phase and amplitude scintillation phenomena has been compiled for use in the testbed. The proposed PLL are connected to the testbed by BP and RBF neural network and FUZZY adaptive PID control method, simulated using MATLAB software to get error changes of the phase locked loop discriminator output by use of different Scintillation severity and noise bandwidth, analysis statistical the phase standard deviation and error cumulative amount of the phase. Finally, through a comparison advantage of three data modulation PID method and the traditional phase-locked loop, Phase-locked to illustrate the impact of different scintillation index and noise bandwidth.
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wang, Teng-Yu, and 王騰嶽. "The investigation of ionospheric scintillation by using ROCAT-1 and GPS data." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/49570829435488657193.
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碩士國立中央大學
太空科學研究所
93
According the data taller from GPS (Global Positioning System) system around Tainan. We calculate the total electron content (TEC) from pseudo range of the GPS signals caused by the delay of ionosphere. According to the carrier to noise (C/N) ratio of the GPS signal, we could estimate the S4 index which represents the degree of the fluctuation of the plasma irregularity in the path of GPS signal with the help of S4 index and the information of the orbit of GPS satellites, we can position the location of the plasma irregularity in the course of the satellite. Once the plasma irregularities are positioned. The spatial distribution of the ionospheric scintillation can thus be realized. Therefore, if we can develop a method to estimate the drift speed and direction of the plasma irregularity from GPS signals, it will be possible to forecast the occurrence of the ionospheric scintillation which will be beneficial to the improvement of the quality of the satellite communication.
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Knight, Mark Frederick. "Ionospheric scintillation effects on global positioning system receivers / by Mark Frederick Knight." Thesis, 2000. http://hdl.handle.net/2440/19809.
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Bibliography: p. 297-304.xxix, 304 p. : ill., col. maps ; 30 cm.
Uses a widely accepted stochastic model of scintillation activity to investigate the effects of scintillations on GPS receivers and systems.
Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 2001?
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Hsueh, Brian Chang Chi. "Simulation and Compensation of Ionospheric Phase Phase Scintillation Noise in Spotlight SAR Data." Thesis, 2009. http://hdl.handle.net/1807/18323.
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This thesis addresses the problem of refocusing smeared SAR images caused by ionosphere phase scintillation noise. A SAR data is smeared when the received signal experiences phase irregularities due to platform orbit deviation, target movement, or, in this thesis, ionospheric scintillation noise due to trans-ionosphere propagation is analyzed. A SAR simulator is constructed to generate stripmap and spotlight data that satisfy theoretically
predicted performances under ideal conditions. The simulator is incorporated with ionospheric phase scintillation models to analyze the broadening effect on system’s PSF. Degraded simulation spotlight data are used to test the proposed compensation algorithm.
This thesis proposes a two-dimensional polynomial phase fitting algorithm to compensate scintillation noise. This work discusses some requirements of the scene in order to carry out the compensation and what is gained and lost in the process. A successful application of the proposed algorithm to TerraSAR-X data is also presented.
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Tsai, Her-Chan, and 蔡和展. "On the Relationship between Equatorial Electrojet and Ionospheric Scintillation measured by FORMOSAT-3/COSMIC." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/n5k36y.
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碩士國立中央大學
太空科學研究所
97
In the day time equatorial ionosphere, there has been often observed a strong eastward current which is called Equatorial Electro-Jet (EEJ). According to the Ampere’s law, the current can induce the magnetic variations in its surroundings. Therefore scientists use magnetic observatories to measure the changes of magnetic field caused by EEJ and study the morphology of Equatorial electrojet. This thesis used the magnetic observatories’ data of International Real-time Magnetic Observatory Network to study the variations of magnetic field caused by Equatorial electrojet. Then we compared the Equatorial electrojet with ionosphere scintillations (represented by S4 values) detected by the FORMOSAT-3 satellites. The main task of this thesis consists of two parts. The first part is to study the morphology of EEJ, while the second part deals with the comparisons between EEJ and ionospheric scintillations. The main purpose of this thesis is using 2007 data sets to study the relationship between EEJ and the magnetic field variations affected by the EEJ under the following conditions: during the days of equinox and solstice; during 10 quiet days near the spring equinox; quiet times during the spring season; and on the May 23 storm day. From analyses of the magnetic field variations affected by EEJ, we found that there existed a seasonal variation in the morphology of EEJ. The seasonal (2007 spring) average location of EEJ is during 9 to 14 LT and ranges from the magnetic latitude 2o N to 3.15o S, while the maximum induced ∆H was about 116 nT. From the statistical comparison between EEJ and scintillation we have the following results: on spring equinox day positive correlation was found between their intensities; 10 days’ and seasonal averages reveal that stronger scintillations occurred near the boundary of EEJ. Moreover, from the comparison of the observations on storm day and quiet days we have the following findings: on storm day the EEJ current has changed it’s direction from that of quiet day pattern; and the average S4 is generally increased in the storm time EEJ region. Both EEJ and ionosphere scintillation change coherently when they have magnitude variations.
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Wu, Meng-Ying, and 吳孟穎. "Phase Scintillation of GPS Signals due to Ionospheric Irregularities in the Equatorial and Polar Regions." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/75e9yv.
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碩士國立臺灣大學
電信工程學研究所
104
Phase scintillations of GPS signals caused by ionospheric irregularities in the equatorial and polar regions are simulated and analyzed. The electron density irregularities in the ionosphere are modeled with different spectra, and realized with a Monte-Carlo technique. A parabolic wave equation (PWE) technique is then applied to compute the field distribution of GPS signals as they propagate through the ionosphere. The simulated phase scintillation in high-latitude regions is much more obvious than that in the equatorial region.
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Yu-HsuanChen and 陳育暄. "Design and Implementation of Real-Time GNSS Software Receiver and its Applications in the Presence of Interference and Ionospheric Scintillation." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/73166070456940363045.
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