A Study Of Time-Dependent 3-D Ionospheric Tomography With Ground-Based GPS Network And Occultation Observations

The Earth's ionosphere is one of the main regions in the solar-terrestrial system. The ionosphere not only protects creatures on the Earth from direct actions of solar UV (EUV) radiation and cosmic energetic particles, but also influences radio propagation through it by reflection, scattering, absorption and refraction. The ionosphere is strongly coupled with the other regions in the solar-terrestrial system, including the sun, the interplanetary medium, the magnetosphere, the thermosphere, and the mesosphere. Because of various disturbances of the Earth's space environment induced by solar activities and plasma instability processes, various irregular structures with widely different spatial scales exist in the ionosphere and the ionosphere is often in disturbed conditions, which influences seriously shortwave communication, satellite communication, navigation and positioning precision of GPS and so on. It's one of the main topics in space weather research to monitor and investigate ionospheric phenomena, reveal physical mechanism of ionospheric phenomena, and analyze the influences of the ionosphere on living environment, which is very important for the development of economy.Computerized Ionospheric Tomography (CIT) is the application of computerized tomography to ionospheric sounding and is suitable for monitoring large-scale spatial structures and disturbances of ionospheric electron density. Time-dependent 3-D CIT with ground-based GPS network observations and GPS occupation measurements is a new technique just at beginning research in recent years, which is of high value to monitor and investigate ionospheric morphology and perturbations. Simulations and inversions based on observations for time-dependent 3-D CIT with ground-based GPS network and occultation observations have been performed in recent years. However, due to the complicated nature of time-dependent 3-D CIT, there still remains lots of questions needed to be studied further, such as the reconstruction formula of time-dependent 3-D CIT with ground-based GPS network and occultation observations should be established, inversion algorithm and computer program of time-dependent 3-D CIT with ground-based GPS network and occultation observations should be developed and so on.The research work discussed in this dissertation aims to image time-dependent 3-D distribution of ionospheric electron density, Ne, in the region to be recovered from the combination of ground-based GPS network measurements and GPS beacon observations obtained by a receiver on board of Low Earth Orbit (LEO) satellite when the GPS satellite is occulted by the surface of the Earth as seen by the receiver. After discussing theoretically the mathematical foundation oftime-dependent 3-D CIT and deducing its reconstruction formula with ground-based GPS network and occultation observations, a new reconstruction method is proposed to perform time-dependent 3-D CIT with relative Total Electron Content (TEC) data. Observations have been processed with the above reconstruction method and some results with important geophysical implications have been obtained. The main research work in this dissertation is the first attempt in China, and also a topic just at beginning research all over the world in recent years. The studies in this dissertation demonstrate that time-dependent 3-D CIT with ground-based GPS network and occultation observations is rather effective to monitor the spatio-temporal evolution of large-scale ionospheric structures. The main results of this dissertation are summarized as follows.1. According to the Fourier transform theory, the projection theorem of ground-based parallel-beam rays and the projection theorem of occultation parallel-beam rays are deduced respectively. Based on the two projection theorems, the reconstruction formula of time-dependent 3-D CIT with ground-based GPS network and occultation observations is established. This research result is innovative and provides the theoretical basis to investigate time-dependent 3-D CIT further.? On the b...