Ionospheric Effects On Satellite Radio Signal Propagation And Its Performance

On the basis of theoretical study on electromagnetic wave propagation in random media, ionospheric effects on radio propagation and the performance of satellite-based radio systems, such as synthetic aperture radar (SAR), have been studied in this dissertation. A thorough search of the relevant literature reveals that the effects of a deterministic ionosphere on satellite radio signal propagation are well known. However, there are many difficulties and issues unsolved in wave propagation in random media. Consequently, this dissertation focuses on stochastic waves and the related ionospheric effects on satellite radio signal propagation. Partly because of the development of satellite-based SAR, this field has become one of hot topics in both ionospheric radio propagation and radar techniques, and is in urgent need of further study. For background purpose a brief review is given on the characteristics of the ionosphere and the theory of satellite radio propagation firstly. The main topics and results of the study are as follows:First, the statistical temporal behavior of satellite signals propagating through the turbulent ionosphere with the slab of irregularities is investigated using the temporal moment and a two-frequency mutual coherence function (MCF), which was obtained by iteration of an integral function. The temporal characteristics include mean arrival time, pulse broadening, skewness and kurtosis. The results show that: 1) the mean arrival time is dominated by the term propagating at group velocity, and small corrections arise from the higher-order dispersion of the background ionosphere and random scattering of irregularities, but the correction from dispersion of irregularities is negligible. 2) Contributions to broadening of trans-ionospheric pulse are mainly from the dispersion of the background ionosphere and scattering of irregularities, while that of dispersion of irregularities is negligible. 3) The temporal skewness of trans-ionospheric pulse is negative, which means its energy is shifted to the leading edge. The contributions from scattering and dispersion of irregularities dominate over those of background. 4) The kurtosis of trans-ionospheric Gaussian pulse is negative and flattened.Second, the second-order statistical characteristics of satellite signals propagating through the turbulent ionosphere and properties of the ionospheric channel are also studied. 1) The property of two-frequency and two-position MCF for a plane wave is numerically studied. 2) Afterwards, the coherence distance and coherence bandwidth of trans-ionospheric pulse have been studied theoretically and numerically. It is found that they increase with both outer and inner scale, more quickly with the former, while theydecrease quickly with increasing of fluctuations of the electron density. 3) In addition, the power impulse response, power spectra and delay-Doppler scattering function of the random ionospheric channel are also derived and discussed by using generalized two-frequency, two-position and two-time MCF.Third, a general scheme and method for solving the symmetrical higher-order moment equation of wave propagation in random media is developed in this dissertation. The available theory for wave propagation in strong fluctuation cases is not satisfied, where the key issue is in solving the moment equation. By adding a non-Gaussian correction to the Gaussian solution to the n+nih order moment equation under complete saturation case, an analytical solution has been obtained for general strong scattering regime. The Gaussian term is the sum of products of the second order moment, while the equation for the non-Gaussian part can be treated by two methods proposed: Green function method and Rytov approximation. As comparison with the Gaussian term, the non-Gaussian term is so small that it can be reasonably treated by the Rytov approximation. The equation for higher-order moment has been treated without restrictions on both the scattering regimes and incident wave sources, thus the analytical solution is general.Fourth, an analytical solution to the fourth-order moment in general strong scattering regime is obtained, and the ionospheric scintillation and correlation of trans-ionospheric radio signals are treated. The solution is general for it is derived in general strong scattering regime and with arbitrary incident wave. Afterwards, the solution for plane wave is obtained and used to treat ionospheric scintillation and correlation of satellite radio signal with verification by experimental data. It is beneficial to solving fourth-order moment and ionospheric scintillation.Finally, ionospheric effects on signal propagation and the performance of imagery of satellite-based SAR are investigated. By using available model for analyzing ionospheric effects on SAR imaging and some results obtained in this dissertation, and the image point spread function, the ionospheric effects on the resolutions of satellite-based SAR are studied. These effects include image shift, geometric distortion, and degradations of resolutions in azimuth and range direction. In addition, the Faraday rotation effect is also discussed.