İyonkürede Elektromanyetik Dalga Yayılım Modeli ve Benzetimi

Abstract

High frequency (HF) electromagnetic wave propagation is important for long distance communication. In HF, the medium for wave propagation is the ionosphere layer of the atmosphere. Ionosphere, which is composed of ionized gasses, is a time varying, inhomogeneous and anisotropic medium. In ionosphere, it is challenging to solve wave equation problems. Existing analytical and numerical methods are insufficient which are applied to solve wave equation in anisotropic an inhomogeneous ionosphere. These methods can be applied only when some physical properties of ionosphere are ignored or some approximations on the wave equation are made. The results obtained with such heavy processing load and long run time methods can not reflect the physical structure of the ionosphere. In some cases run time gets longer than the time that the structure of the ionosphere changes, so that the result can not be valid for the ionosphere which is desired to be modeled. The performance of long distance communication technology increases, when the models of ionosphere and wave propagation are close to the reality. So there is a demand for a new approach arises to model wave propagation through the ionosphere and represent the physical properties of the ionosphere in iv this model. In this thesis, a novel and unique HF wave propagation model is developed. This model is composed of ray tracing representation of wave and 3 Dimensional (3D) spherical voxel model of ionosphere. Ray tracing is applied as a geometrical optics approach. Snell’s law is used as a ray tracing technique. The well known Appleton-Hartree formula is used for calculation of refractive index, which is a critical parameter of ray tracing with Snells law. Appleton-Hartree formula represents physical parameters of ionosphere and in the developed model, all components of the formula are covered. Wave incident to the ionosphere splits into two waves, which are ordinary and extraordinary waves, as a result of anisotropic structure of the ionosphere. In the wave propagation model developed in this thesis, ray tracing is applied for each of ordinary and extraordinary waves through 3D spherical voxel model of the ionosphere. 3D spherical voxel structure of represents the inhomogeneous structure of the ionosphere. Parameters of the ionosphere are calculated for each voxel for each given time. So that time dependency of ionosphere is also fulfilled by the model. The parameters of the ionosphere is calculated using IRI-Plas software tool. IRI-Plas can be assimilated with data to represent the state of ionosphere better. IONOLAB-RAY provides Total Electron Content data automatically and using IRI-Plas, gives the opportunity to assimilate date to the ionosphere model. IONOLAB-RAY algorithm is developed to implement wave propagation and ionosphere models generated in this study and to apply on engineering applications. IONOLAB-RAY is composed of preprocess and mainprocess phases. For the region of interest and time defined by the user, calculations which need relatively longer time and proper to do previously are done in preprocess phase. In mainprocess desired scenarios can be run in the given region of interest and time. All of the parameters needed in calculation of wave prov pagation in the ionosphere are calculated automatically by the modules of the IONOLAB-RAY. Multiple runs can be applied for sets of values of input parameters with one command and all combinations of the scenarios can be run. The format of outputs is available for engineering studies and analysis. IONOLAB-RAY includes modules to calculate wave parameters such as, attenuation, time delay, phase velocity, group velocity and Faraday rotation. These parameters can also be inputs of channel models of long distance communication. Data assimilation to the IONOLAB-RAY based on statistical models is available. This property enables to examine the statistical variation of wave propagation paths and arrival positions on Earth. Wave paths with respect to different locations on Earth, days in year and times in day are generated using IONOLAB-RAY, which is developed in the scope of this thesis study. Results depending on the variations in the input parameters are obtained. The effects of data assimilation into the ionosphere model is observed. All of the results are examined. IONOLAB-RAY algorithm is compared with other limited studies in the literature, which have the same purposes with IONOLAB-RAY, and compatible results are obtained under the limitations of major differences of the models. Ionograms are produced using IONOLAB-RAY algorithm and compared with measured ionograms. So that IONOLAB-RAY is validated over the comparisons both with simulations and measurements.