Ionospheric Tomographic Technology And Applications

With more than10years of development, GPS-based ionospheric tomography has been an important means of ionospheric sounding which can conquer limitations of the traditional single-layer ionosphere model that can only reflect the horizontal structure of ionosphere but difficultly for vertical structure. And it will exhibit great scientific value and application advantages in monitoring and studying the three-dimensional internal structure, variation and disturbances of ionosphere. Although the theory and technology has been improving increasingly, but there are some defects and shortcomings need to be further researched in practical application. Consequently, an improved method of ionospheric tomography is proposed in this article based on a detailed analysis of some problems in the GPS-based ionospheric tomography. Based on the above method, we investigate the modeling and forecast of four-dimensional ionosphere by using neural network method. In addition, we study the temporal-spatial variations of ionospheric electron density under the condition of pre-seism by using GPS observations derived from IGS. Some interesting results are obtained from the reconstructed ionospheric images. In generally, the main work and results of this dissertation is summarized as follows:1. By detailedly introducing and analyzing the principle of GPS-based ionospheric tomography and inversion algorithm, we found that low accuracy of iteration initial value and limitation of spatial distribution of GPS rays will lead to the reconstructed image distortion of ionospheric electron density to some extent. To resolve the above problem, an improved method of ionospheric tomography is proposed. In this method, the single-layer ionosphere model and ionopheric tomography model are combined and we use sufficient TEC data interpolated by the single-layer ionosphere method to improve the overall quality of ionospheric tomography. Inverted results from actual GPS observations demonstrated its effectivity to the reconstruction of ionospheric electron density distribution. The new method improves the reconstructed image quality of ionospheric tomography manifestly, especially in the case of insufficient TEC data and space weather anomalies.2. By combing the GPS observations provided from Hong Kong CORS, we use the neural network method to model and forecast of the electron density derived from ionospheric tomography and validation and analysis is conducted to its results. The results show that the precision of the predicted electron density value within30minutes and60minutes can respectively arrive at0.45TECU and1.34TECU. Comparing with the ionospheric electron density derived from the IRI2007model, its precision has improved greatly. The method can also give the three-dimensional ionospheric electron density under the condition of equal accuracy with single-layer ionosphere model.3、 The temporal-spatial variations of the ionosphere over the epicenter region of Japan March11,2011earthquake are investigated by using the ionospheric tomography technology and the GPS dual-frequency data provided from IGS stations of Japan and adjacent area. By analyzing the reconstructed images of11days before the earthquake combined with the2times standard deviation detection method, we can conclude that the abnormal ionospheric electron density decreases appeared in February28UT14:00～16:00and the abnormal ionospheric electron density increases appeared in March2UT08:00～14:00, March3UT00:00～06:00and March4UT12:00～20:00are most likely related with Japan3.11earthquake.