A New4-Dementional Ionosphere Tomography Algorithm And Its Application

The single-layer ionosphere model cannot present the space distribution characteristics of the ionosphere electron density, while the vertical structure of the ionosphere aresignificant to the ionospheric physics study and the monitoring of space environmental change. The Computerized Ionospheric Tomography (CIT) provides a way to study the ionosphere vertical structure, as the ionosphere are divided into several layers with CIT, weakening the error from the single hypothesis and projection function symmetry. The CIT not only has great advantage in monitoring the space environment change, but also in providing the ionosphere delay correction for the single frequency positioning users. Currently, the CIT research has been greatly developed from algorithm study to the theory application.Due to the impact of station distribution and poor observation condition, the some key problems as the reliable CIT algorithmremain to be further perfected and improvedA new ionosphere tomography algorithm with two-grids’constraints and3D velocity images is proposed in this paper. Besides, as the DORIS VTEC has higher accuracy than the GPS TEC for the high ratio of the two frequency observations, a new algorithm to get absolute DORIS TEC combining the GIM TEC and DORIS ATEC are presented. Then the GNSS TEC, DORIS TEC and Altimeter TEC are simultaneously used to set up the four-dimensional ionosphere model. The effectiveness and advantages of the model are validated and discussed in space positioning application and the space environment change monitoring. Some conclusions are given in the paper.The main work of this dissertation is summarized as follows,(1) The ionosphere variation velocity is estimated using the DORIS carrier observations,and the accuracy assessment index is proposed to ensure the reliability of the velocity parameter.. After that, a new cycle slip detection algorithm are presented for DORIS data preprocess. The new algorithm is tested by using the HY2A DORIS data. To take advantage of the high accuracy of DORIS TEC, Firstly the parameter initial estimation is conducted based on GIM TEC. By taking the initial estimations and the accuracy information as the virtual observations, we modify the initial estimations epoch by epoch using the DORIS ΔTEC data. Finally, the2D regional ionosphere model is established in a new satellite-station way and its application in HY2A data process around the Mediterranean region is presented.(2) The CIT is typical ill-posed problem. Using the ionospherepriori information as the constraints to improve the state of normal equation is an effective approach to solve this problem. In this paper, we impose priori constraints by increasing the virtual observationsbetween the two-grids which greatly improve the state of normal equation. Based on this, to obtain the real time velocity information of ionosphere electron density, the grid electron density velocity parameters are introduced, which can be estimated with electron density parameters simultaneously. Three groups of experiments are designed to verify the basic principle of the new algorithm with simulated date. Further, the4D images of the ionosphere electron density variation are inverted around Europe on08/15/2003with quite geomagnetic condition. The results are compared with the variation time series of electron densityobserved by ionosonde among different layers in the paper.(3) Multidimensional ionospheric model can weaken the impact from the single hypothesis and projection function symmetry. Here in this paper the ionosphere delay corrections are calculated based on the four-dimensional ionosphere model, and then are provided to the single frequency positioning users. The two groups of experiments are designed todiscuss the advantage of multidimensional ionospheric model in spatial positioning application, while the two experiments’areasare chosen in Australia and Europerespectively. With the introduction of the independent and external check stations, the TEC from the4D model are compared with the double-frequency TEC, GIM TEC and IRI TEC. It is found that the4D model TECs have more accuracy when the elevation angles are low than the GIM TEC and IRI TEC. Under the severe geomagnetic condition, the position accuracy can be improved by25%on horizontaldirection, and20%on vertical direction. The multidimensional ionospheric model shows a good application prospect under extreme ionosphere condition.(4) The GNSS TEC, DORIS TEC and Altimeter TEC are combined to inverse the four-dimensional electron densitydistribution around the Tohoku earthquake time, and also the ionosonde and World-Wide Lightning Location Network data. Comparing with the images on Feb.18-Feb.20with quite geomagnetic condition, even the Kp index and Dst index is relatively low on Mar.8, the ionosphere abnormal are obviously detected on that day. Especially on layer300km-500km around the epicenter, there is a cycle wave shape abnormal propagating to the vertical and horizontal directions,and the propagation distance and amplitude of the abnormal on vertical direction is larger than the horizontal direction. Meanwhile the waveform center is not right above the epicenter, but shifting to the longitude144(?) surface. There is apparent velocity increase on layer100km-200km around the epicenter, even to compare the Mar.8’images with Mar.7’images, the grid velocities show greatly enhancement at this area. Those regional ionosphere abnormal is likely related to birth and occurrence of2011Tohoku earthquake.