On GPS-based Ionospheric Tomography Algorithm And Its Application

Ionospheric electron density is defined as the number of free electrons per unit volume, which is one of the important physical parameter for ionosphere. Its disturbance not only affects radio wave propagation in the ionosphere, but also is a strong indirect reflection of crustal movement. Therefore, study of ionospheric electron density perturbations-have important practical significance to seismic monitoring and early warning. With the rapid development of global navigation satellite system and ionosphere sounding technology, GNSS-based three-dimensional reconstruction of the ionospheric electron density technology: ionospheric tomography technology, become an efficient and reliable method for ionospheric sounding.Due to its high precision, low cost and real-time detection, it is suitable for monitoring three-dimensional distribution of ionospheric electron density and its perturbations. Based on the theory of computerized tomography, this dissertation systematically explains basic principles and methods of computerized ionospheric tomography, and puts emphasis on several key aspects of the ionospheric electron density inversion and code implement. The main contentsare as follows:(1) Intensive study on the GPS data pre-processing, selecting discretization basis function, judging of effective ray and establishing coefficient matrix for the reconstruction process of computerized ionospheric tomography;(2)Detailedstudy on the reconstruction algorithm of computerized ionospheric tomography. And the selection method of the optimal relaxation factor for multiplication algebraic reconstruction algorithm has been improved to optimize the algorithm;(3) Developing programs for ionospheric tomography based on the ground GPS data using IDL language;(4) Using the above software, based on more than 150 GPS stations continuous operation observation data in Japan region, reconstructed the ioonospheric electron density distribution on March 8,2011(3 days before 3·11 Tohoku earthquake) and March 11,2011 (co-seismic day), and analyzed the results carefully.