International Telemetering Conference Proceedings / October 26-29, 1992 / Town and Country Hotel and Convention Center, San Diego, California / The ionosphere is a critical link in the earth's environment for space-based navigation, communications and surveillance systems. Signals sent down by the GPS satellites can provide an excellent means of studying the complex physical and chemical processes that take place there. GPS uses two frequencies to ascertain signal delays passing through the ionosphere. These are measured as errors and used to correct position solutions. Since this process is a means of measuring columns of Total Electron Content (TEC), multiple top-soundings from the GPS constellation could provide significant detail of the ionospheric pattern and possibly lead to enhancement of predictions for selectable areas and sites. This paper addresses transforming the GPS propagation delays (errors) into TEC and providing TEC contours on a PC-style workstation in real and integrated time and discusses a worldwide ionospheric network monitoring system.

京都大学 / 0048 / 新制・課程博士 / 博士(情報学) / 甲第19133号 / 情博第579号 / 新制||情||101(附属図書館) / 32084 / 京都大学大学院情報学研究科通信情報システム専攻 / (主査)教授 山本 衛, 教授 津田 敏隆, 教授 佐藤 亨 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DGAM

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

GPS integrated Total Electron Content measurements received at the ground or in space are used for tomographic reconstruction of the ionospheric electron density distribution. The IRI/GCPM model is used as initialisation of the tomographic MART algorithm. During the procedure GPS TEC data are iteratively assimilated to the model. To test the potential of the reconstruction, electron density profiles from IRI/GCPM and the assimilation are compared with ionosonde measurements and CHAMP radio occultation profiles for dates during the HIRAC campaign in April 2001. All profiling methods show electron density values of similar magnitude. It is shown that including TEC GPS data corrects the model towards the ionosonde measurements. / Integrale Messungen der Elektronendichte aus GPS-Boden- sowie Radio-Okkultations-Messungen bilden die Datenbasis der hier vorgestellten 3-dimensionalen Tomographie der ionosphärischen Elektronendichteverteilung. Zur Initialisierung des verwendeten iterativen MART Algorithmus wird das IRI/GCPM Modell verwendet, wobei das Modell während der Iteration sukzessiv an die Messdaten angepasst wird. Um das Potential des Verfahrens abzuschätzen, werden Elektronendichteprofile des IRI/GCPM Modells und der Rekonstruktion mit Ionosondenmessungen und CHAMP Okkultationsprofilen verglichen. Dafür wurden Messungen während der HIRAC Kampagne im April 2001 genutzt. Alle hier gezeigten Profilableitungen geben Elektronendichtewerte der selben Größe wieder. Eine Annäherung des IRI/GCPM Modells an die Messwerte der Ionosonde durch die Assimilation der TEC GPS Daten wird gezeigt.

Am DLR Neustrelitz wird kontinuierlich die totale Ionosation der Atmosphäre bestimmt und globale Karten der vertikal integrierten Elektronendichte erstellt. Es werden dazu die Signale der Navigationssatelliten-Systeme GPS und GLONASS verwendet. In dieser Arbeit wird die Verteilung des totalen Elektronengehalt (TEC) oberhalb der mittleren Breiten während der Übergangssaison September bis November 2004 auf langperiodische Variationen im Bereich von mehreren Tagen sowie zonalen Wellenzahlen bis zu 5 untersucht. Die Ergebnisse werden mit einer Analyse von planetaren Wellen aus assimilierten Stratosphärendaten, Radardaten für Temperatur vom Collm Observatorium (51.3◦N, 13.0◦O) und Beobachtungen der kritischen Plasmafrequenz der F2-Schicht (f0F2) mit der Ionosonde in Juliusruh (54.6◦N, 13.4◦O) verglichen, um den meteorologischen Einfluss auf die Variation der Ionosphäre zu studieren. / The DLR Neustrelitz regularly produces maps of the total total electron content (TEC) on a global scale using the navigation satellite systems GPS and GLONASS to forecast space weather. In this study we turn our attention to the higher middle latitudes TEC variations during September to November 2004 in a long-period range of several days with a zonal wavenumber up to 5. The results are compared with a planetary wave analysis using assimilated stratospheric data, mesosphere/lower thermosphere radar temperature data at Collm observatory (51.3◦N, 13.0◦E) and the ionosonde observed critical plasma frequency of the F2-layer (f0F2) at Juliusruh (54.6◦N, 13.4◦E) to investigate the meteorological influences on ionospheric variability.

Após a desativação da disponibilidade seletiva, ocorrida em maio de 2000, a maior fonte de erro presente no sistema GPS passou a ser a refração ionosférica. Os seus efeitos provocam um avanço na fase de batimento da portadora e um atraso no código. Na região equatorial onde o Brasil está inserido, a refração ionosférica apresenta variações que decorrem de diversos fatores tais como: o ciclo solar, o movimento aparente do Sol, as estações do ano, o campo geomagnético, entre outras. Desta forma, a refração ionosférica é um fator limitante pois, degrada a determinação de posições, principalmente, se o usuário estiver utilizando um receptor de apenas uma freqüência. Para avaliar o efeito da refração ionosférica no Brasil, no período compreendido entre janeiro de 1997 a dezembro de 2001, foram utilizados dados coletados com receptores providos de duas freqüências e que integram a Rede Brasileira de Monitoramento Contínuo do Sistema GPS. Todos os dados foram preparados e inseridos em um programa científico de processamento das observáveis do sistema GPS. Devido à grande massa de dados foi necessário o desenvolvimento de um programa para verificar a integridade dos mesmos, converter as efemérides precisas e os dados para o formato de entrada do programa científico e preparar os arquivos de lote. Além das características apresentadas, este programa foi desenvolvido para automatizar o processo de cálculo do conteúdo total de elétrons. Ao final do processamento o programa exibe os parâmetros que representam a refração ionosférica ou seja, os valores calculados para o Conteúdo Total de Elétrons. Tais valores permitiram a criação de uma série histórica do comportamento da refração ionosférica abrangendo um intervalo de tempo que contempla um período em que o ciclo solar apresentava atividade mínima e um outro período em que o ciclo solar alcançou a máxima atividade. Estes dados indicam o comportamento da ionosfera para um período de cinco anos em uma das regiões do planeta que apresenta as maiores variações, comportamento este, que permitirá um melhor conhecimento da ionosfera e a melhoria ou desenvolvimento de modelos mais adequados. Foram gerados ainda, mapas da ionosfera que poderão auxiliar na melhoria da acurácia posicional. / Since the US president decided to turn off the selective availability (SA) one of the biggest error in the GPS system has been the ionosphere refraction. The refraction effect on GPS signals are: delay for the code and an advance for the phase. In the equatorial region, where Brazil is, the refraction presents the biggest variations that are caused by the solar cycle, the time of the day, the season, the geomagnetic field and many others phenomena. In this case, the ionosphere refraction is a limitation because it increases the degradation of the position, specially if the user is using a single frequency receiver. To evaluate the ionospheric effects in Brazil, between January 1997 and December 2001, data from the Brazilian Continuous GPS Monitoring Network were used, provided by double frequency GPS receivers. All data were prepared and used by a scientific software to process the GPS observations. The volume of data was so big that it was necessary to write a software to manage the data integrity, to transform the precise ephemeris and the observations to scientific program format and to create batch files. Also, the program was used to process the data and to compute the total electron content automatically. At the end of the process, the software shows the TEC parameters. These parameters were used to create a historical series of the ionosphere refraction in Brazil. This series represents a period of minimal solar cycle, 1997, and a maximum period of the solar cycle, 2000 / 2001 in one of the most active regions of the planet. This series will improve the knowledge on the ionosphere and will allow to improve models or create new ones. Ionospheric maps that can be used to improve the positional accuracy, were also generated.

Certain modern radio systems that rely on trans-ionospheric propagation require knowledge of changes in total electron content (TEC). Understanding rapidly changing, small amplitude perturbations in the ionosphere is important in order to quantify the accuracy of those systems. The main aim of this thesis is to collect statistical information on the perturbations and wave structures present in the ionosphere, for use in radio astronomy calibrations and future communication systems planning. To gain this information, TEC calculated from instruments measuring Faraday rotation on signals from geostationary satellites were used. These measurements were collected in Italy over the period of 19751982 and 1989-1991 at one minute intervals. An important class of TEC fluctuations is travelling ionospheric disturbances (TIDs). Here, temporal variations of mid-latitude slant TEC measurements during two solar cycle phases, i.e solar minimum in 1975-1976 and solar maximum in 1989-1990, were studied. Direct inspection of Savitzky-Golay filtered TEC data was used to extract the amplitudes of TIDs. Fourier analysis was used to extract the most dominant periods of the TIDs. Discrete Meyer wavelet together with the ANOVA method to determine TID variation changes in different parts of the day. Another class of TEC fluctuations presented in this thesis is diurnal double maxima (DDM) structures. These structures were observed during mid-day in our TEC measurements between 1975 and 1991. Verification of the DDM observations was sought by using foF2 and hmF2 measurements from an ionosonde in RomeA combination of ionospheric 3-D tomographic imaging and ray propagation theory has been used for the first time to demonstrate a method that can show how the new European radio array LOFAR will be affected by the ionosphere. This was achieved from a case study of a geomagnetic quiet day ionosphere by simulating how ray propagations, at different elevations and frequencies, will behave as they traverse the ionosphere. The important result from this study was that continuous monitoring of the telescope will be important during operation of the array if the errors introduced by the ionosphere are to be accurately corrected for. The study of TEC changes over different short time windows demonstrated that the ionosphere vastly varies over short time scales, thus making the monitory non trivial. Statistical analysis of the TEC changes will also be useful to the new European GPS augmentation system EGNOS as an indicator on whether the ionospheric measurements from the system are realistic.

The Global Positioning System (GPS) has been used for more than a decade for the accurate determination of position on the earth's surface, as well as navigation. The system consists of approximately thirty satellites, managed by the US Department of Defense, orbiting at an altitude of 20 200 kilometres, as well as thousands of stationary ground-based and mobile receivers. It has become apparent from numerous studies that the delay of GPS signals in the atmosphere can also be used to study the amosphere, particularly to determine the precipitable water vapour (PWV) content of the troposphere and the total electron content (TEC) of the ionosphere. This dissertation gives an overview of the mechanisms that contribute to the delay of radio signals between satellites and receivers. The dissertation then focuses on software developed at the Hartebeesthoek Radio Astronomy Observatory's (HartRAO's) Space Geodesy Programme to estimate tropospheric delays (from which PWV is calculated) in near real-time. In addition an application of this technique, namely the improvement of tropospheric delay models used to process satellite laser ranging (SLR) data, is investigated. The dissertation concludes with a discussion of opportunities for future work. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2004.

The Global Positioning System (GPS) has been used for more than a decade for the accurate determination of position on the earth's surface, as well as navigation. The system consists of approximately thirty satellites, managed by the US Department of Defense, orbiting at an altitude of 20 200 kilometres, as well as thousands of stationary ground-based and mobile receivers. It has become apparent from numerous studies that the delay of GPS signals in the atmosphere can also be used to study the amosphere, particularly to determine the precipitable water vapour (PWV) content of the troposphere and the total electron content (TEC) of the ionosphere. This dissertation gives an overview of the mechanisms that contribute to the delay of radio signals between satellites and receivers. The dissertation then focuses on software developed at the Hartebeesthoek Radio Astronomy Observatory's (HartRAO's) Space Geodesy Programme to estimate tropospheric delays (from which PWV is calculated) in near real-time. In addition an application of this technique, namely the improvement of tropospheric delay models used to process satellite laser ranging (SLR) data, is investigated. The dissertation concludes with a discussion of opportunities for future work. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2004.

Após a desativação da disponibilidade seletiva, ocorrida em maio de 2000, a maior fonte de erro presente no sistema GPS passou a ser a refração ionosférica. Os seus efeitos provocam um avanço na fase de batimento da portadora e um atraso no código. Na região equatorial onde o Brasil está inserido, a refração ionosférica apresenta variações que decorrem de diversos fatores tais como: o ciclo solar, o movimento aparente do Sol, as estações do ano, o campo geomagnético, entre outras. Desta forma, a refração ionosférica é um fator limitante pois, degrada a determinação de posições, principalmente, se o usuário estiver utilizando um receptor de apenas uma freqüência. Para avaliar o efeito da refração ionosférica no Brasil, no período compreendido entre janeiro de 1997 a dezembro de 2001, foram utilizados dados coletados com receptores providos de duas freqüências e que integram a Rede Brasileira de Monitoramento Contínuo do Sistema GPS. Todos os dados foram preparados e inseridos em um programa científico de processamento das observáveis do sistema GPS. Devido à grande massa de dados foi necessário o desenvolvimento de um programa para verificar a integridade dos mesmos, converter as efemérides precisas e os dados para o formato de entrada do programa científico e preparar os arquivos de lote. Além das características apresentadas, este programa foi desenvolvido para automatizar o processo de cálculo do conteúdo total de elétrons. Ao final do processamento o programa exibe os parâmetros que representam a refração ionosférica ou seja, os valores calculados para o Conteúdo Total de Elétrons. Tais valores permitiram a criação de uma série histórica do comportamento da refração ionosférica abrangendo um intervalo de tempo que contempla um período em que o ciclo solar apresentava atividade mínima e um outro período em que o ciclo solar alcançou a máxima atividade. Estes dados indicam o comportamento da ionosfera para um período de cinco anos em uma das regiões do planeta que apresenta as maiores variações, comportamento este, que permitirá um melhor conhecimento da ionosfera e a melhoria ou desenvolvimento de modelos mais adequados. Foram gerados ainda, mapas da ionosfera que poderão auxiliar na melhoria da acurácia posicional. / Since the US president decided to turn off the selective availability (SA) one of the biggest error in the GPS system has been the ionosphere refraction. The refraction effect on GPS signals are: delay for the code and an advance for the phase. In the equatorial region, where Brazil is, the refraction presents the biggest variations that are caused by the solar cycle, the time of the day, the season, the geomagnetic field and many others phenomena. In this case, the ionosphere refraction is a limitation because it increases the degradation of the position, specially if the user is using a single frequency receiver. To evaluate the ionospheric effects in Brazil, between January 1997 and December 2001, data from the Brazilian Continuous GPS Monitoring Network were used, provided by double frequency GPS receivers. All data were prepared and used by a scientific software to process the GPS observations. The volume of data was so big that it was necessary to write a software to manage the data integrity, to transform the precise ephemeris and the observations to scientific program format and to create batch files. Also, the program was used to process the data and to compute the total electron content automatically. At the end of the process, the software shows the TEC parameters. These parameters were used to create a historical series of the ionosphere refraction in Brazil. This series represents a period of minimal solar cycle, 1997, and a maximum period of the solar cycle, 2000 / 2001 in one of the most active regions of the planet. This series will improve the knowledge on the ionosphere and will allow to improve models or create new ones. Ionospheric maps that can be used to improve the positional accuracy, were also generated.