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

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Modeling of the ionosphere has been a highly interesting subject within the scientific community due to its effects on the propagation of electromagnetic waves. The development of the Global Positioning System (GPS) and creation of extensive ground-based GPS networks started a new period in observation of the ionosphere, which resulted in several studies on GPS-based modeling of the ionosphere. However, software studies on the subject that are open to the scientific community have not progressed in a similar manner and the options for the research community to reach ionospheric modeling results are still limited. Being aware of this need, a new MATLAB&reg / based ionosphere modeling software, i.e. TECmapper is developed within the study. The software uses three different algorithms for the modeling of the Vertical Total Electron Content (VTEC) of the ionosphere, namely, 2D B-spline, 3D B-spline and spherical harmonic models. The study includes modifications for the original forms of the B-spline and the spherical harmonic approaches. In order to decrease the effect of outliers in the data a robust regression algorithm is utilized as an alternative to the least squares estimation. Besides, two regularization methods are employed to stabilize the ill-conditioned problems in parameter estimation stage. The software and models are tested on a real data set from ground-based GPS receivers over Turkey. Results indicate that the B-spline models are more successful for the local or regional modeling of the VTEC. However, spherical harmonics should be preferred for global applications since the B-spline approach is based on Euclidean theory.