Research On Analying And Simulation For Effect Of Ionosphere To The Orientqtion Of Radar Signal & Navigation Satellite

Based on the spatial-temporal characteristics and physical models of the ionosphere, the aim in the thesis is to analyze and simulate the effects of the ionosphere on the radar and navigation satellites. A series of theoretical and technical issues of the ionospheric effects are systematically studied. This thesis focuses on the ionospheric effects on the space-borne synthetic aperture radar (SAR), techniques and methods of ionospheric delay correction for navigation satellites. The main topics and results of the study are as follows.1. Visualization of spatial-temporal characteristics and analysis of ionosphere. First, several different physical modals of the ionosphere are introduced, then the calculation of ionospheric models, as well as the spatial and temporal coordinate systems are comprehensively summarized. And time transformation is thoroughly expatiated, calculation of the ionospheric models showed by 2D graphs and 3D visualization expressions is used for analyzing the spatial-temporal characteristics of the ionosphere. After that the storage and expression of electron density are realized based on ochre. The analysis of visualization indicated that the ionosphere which distributes along with altitude and latitude possesses obvious features. Compared the error of data calculated by physical modals of the ionosphere with practical observed, the result showed that 80% of the differences between calculated data and practical observed date are less than 10 TECU. It shows it is a better method which researched ionosphere with ionosphere model calculating data.2. The analysis and simulation of the ionospheric effect on the radar. Theoretical formulas of the ionospheric effects on ground-based radar for measuring distance , angel , speed and height are thoroughly derivate, then the working principle of space-borne SAR is expatiated and ionospheric effects on uncompressed azimuth resolution and analysis of the ionospheric effects on compressed azimuth and range resolution of space-borne SAR are derivate. Based on derivate theoretical formulas, numerical simulation of the effects of ionopheric dispersion broadening on range resolutions of different kind of band of space-borne SAR is completed. The results of simulation present that the ionospheric effects on X, C-band of space-borne SAR are negligible, on P-band and the followings must be taken into account. In addition, a method of scaling analyzing the ionospheric effects on radar image data is proposed and the COSMO radar data and optical images under different weather conditions are used for analyzing the effects of a background ionosphere and ionospheric perturbations on radar imaging. The results show that theoretical analysis and experimental results are in good agreement. It shows the theoretical analysis and simulation is veritable and credible.3. A trajectory design method of SAR satellite considering ionospheric effects. First, basic theory and general methods of trajectory design are briefly introduced. Based on previous conclusions and results of relevant literature, a trajectory design method of SAR satellite considering and weaken the ionospheric effects on P-band and the followings by reasonable trajectory design and prediction is proposed. Then the geometric relationship between space-borne SAR and ground points including distance, elevation angle, azimuth angle and their rate of changing is deduced. J2/J4 and MSGP trajectory recursive and predicting solver are introduced, simulation of space-borne SAR is also realized by use of MSGP trajectory recursion and two-line orbit elements published by NORAD. 4. Based on the analysis and derivation of ionospheric effects on the navigation system and correction methods, a interpolation algorithm of VETC associated with space-time is proposed, the effect of several typical ionospheric anomalies on GPS measurements is analyzed. The present in-orbit Satellite Navigation and Positioning Systems are also introduced, as well as the time and coordinate systems, signal frequency of GPS,GLONASS and Galileo. Then visualization of the present in-orbit satellites navigation and positioning constellation are realized, higher-order theoretical formula for correcting three-frequency ionospheric refractive error, theoretical first-order formula for correcting two-frequency ionospheric refractive error in GPS and Galileo are both derivate. Several commonly used models of monolayer ionospheric delay correction models are summarized and a method using the combination correlation coefficient and wavelet analysis to predict sunspots or solar radio flux is proposed in the course of confirming the parameters of ionospheric delay correction models. And then the better wavelet basises are chose by analyzing the experimental results of using each wavelet basis, based on the observations of ionospheric delay correction, the accuracies of several VTEC data provided by IGS Web site are analyzed and compared, the results of comparison show that accuracy of the intraday and fast processing VTEC data provided by IGS Web site can meet the requirement for single-frequency ionospheric delay correction and other purpose. In order to increase the grid's space and time resolution, a VTEC interpolation algorithm based on temporal-spatial correlations is deduced and we can find this algorithm achieves a good result by comparing the interpolation data and 15 minutes of data on the Web site. After that, effects of ionospheric delay correction on the accuracy pf dual-frequency GPS observation data are analyzed. Finally the effects of ionospheric perturbations on GPS observations are analyzed by using the data provided by IGS which are gotten before and after solar storms in 4 August 2010 and when earthquake happened in Japan in March 11, 2011.