Ionosphere And Its Effects On Radio Wave Propagation

On the basis of theoretical study of electromagnetic wave propagation and scatteringin random media, the background ionosphere and the electron density irregularities thatlocate in the ionosphere which effect on the radio wave propagation have been studiedin this dissertation. From the status of current research and the open questions in thisarea we can see that there are still many uncertain factors and the outstanding issues inthis area due to the complexity of the ionospheric random medium itself, and which hasseriously influence on the normal operation of the radio wave system and its workefficiency improving. Therefore, the thesis will focus primarily on researching somecharacteristics of the ionosphere itself and its various effects on radio wave propagation.The research contents include: the temporal and spatial distribution characteristics of theionospheric conductivity, the drift characteristics of the ionospheric electron densityirregularities, the ion velocity distribution function and its characteristics of theincoherent scattering, the ionospheric scintillation, as well as the characteristics of thetime delay and the frequency shift for the radio wave propagation, which are all thecurrent hot issues in this field. The main topics in the dissertation are as follows:Firstly, the changes of the Pedersen and Hall conductivity for four different solaractivity phase in the high latitude ionosphere is discussed, and the winter abnormaldistributon of the conductivity in the F2layer is also analyzed. In addition, therelationship between the ionospheric conductivity and the ionizing consumption whichtakes place in the F layer and the electronic Joule heating which appears in the E-layerat the storm time are all studied.Secondly, the drift velocity of the ionospheric irregularities for the calm and the stormtime is inversed. Meanwhile, based on the space receiver technology and the“multi-station one satellite” method, the drift velocity of the ionospheric irregularitieshas been estimated successfully, and the estimated results were compared with theresults that obtained from the time power spectra method finally.Thirdly, with the relative larger electric field strength, the torus velocity distributionfunction for ions is obtained at the high latitude ionosphere, and the characteristic of thetorus velocity distribution function is also simulated and analyzed. Meanwhile, takinginto account the ion temperature anisotropy, the collision with other ions and itsvariation with the ionospheric electric field, the incoherent scattering power spectrum ofion in different direction is simulated and discussed.Fourthly, the ionospheric scintillation data of GPS L-band in mid-latitude of HainanChina for the period of July1991to July1993during the lower solar activity isstatistically analyzed. Meanwhile, takes the year of the lower solar activity as a timenode, the high-latitude ionospheric scintillation data which comes from the INGV (Istituto Nazionale di Geofisica e vulcanologia) scintillation monitoring networks ofItalian as well as from the Zhongshan Station of China for a period of one year are alsostatistically analyzed and discussed. At the same time, the scintillation characteristics atthe mid-latitude ionosphere are compared with it at the high latitude region at the GPS Lfrequency band is given.Finally, assuming that the ionosphere is a homogeneous, isotropic, stratified media, theDoppler shift formula of the echo signals of the radio wave is derived. And with theassumption of the Rayleigh fading, the probability density distribution of the multi-pathtime delay and the Doppler shift of the ionospheric radio signal are also derived,moreover, the probability density distribution of the time delay, the average power ofthe received signal, and the received signal variance changes with the time delay spreadare discussed in detail. Moreover, based on the theory of the multiple phase screen(MPS), the echo field expression that the radio wave propagates through the ionosphereup and down (i.e. double path propagation) are obtained. The research shows thatcomparing with the geometrical optical approximation (GO), the method of the multiplephase screen no only takes into account the changes of the amplitude of the radio wave,but also considering the variation of the phase, and its advantages is obvious.