Research On Ionospheric Effects And Error Calibration For Spaceborne Interferometric Synthetic Aperture Radar

Spaceborne interferometric synthetic aperture radar(InSAR)is the synthesis of conventional SAR techniques and interferometry,in which the interferometric phase of SAR image pairs is used as an original information source to obtain three-dimensional topography information via a series of InSAR processing.It can work to obtain high-precision,fine resolution digital elevation model(DEM)in a wide scene in nearly all weather conditions day and night.Spaceborne InSAR has been widely used in many applications,such as the global high-precision DEM mapping,monitoring the crustal deformation and so on.Today,spaceborne InSAR systems are developing in the direction of low-frequency,fine-resolution,high-precision.However,the ionosphere severely affects SAR signal at microwave band.The effects include dispersion,group delay,scintillation,Faraday rotation.These will restrict the development of to-be spaceborne InSAR systems.This paper focuses on the effects of the ionosphere on spaceborne InSAR systems.Two relevant problems,i.e.analyzing and correcting the ionospheric effects,are investigated systematically.The major work of this paper is listed as followsIntroduction is presented in Chapter 1.It sets forth the background and significance of this dissertation,and then summarizes the status of spaceborne InSAR systems,and research situation of analysis and calibration of the effects of the ionosphere on spaceborne InSAR systems.Finally the arrangement of this paper is presented.The basic theory of the ionosphere and the wave propagation theory in the ionosphere are introduced in Chapter 2.Firstly,the basic theory of the ionosphere and its medium characteristic is presented,indicating that the ionosphere can be studied in two parts: background ionosphere and the ionospheric irregularities.Secondly,the wave propagation theory in background ionosphere and irregularities is expatiated on.The effects of the ionosphere on spaceborne InSAR systems are studied in Chapter 3.Firstly,the principle of repeat-pass spaceborne InSAR is introduced.Secondly,several effects of the ionosphere on InSAR are gradually studied,such as the effects of the ionosphere on SAR image signal-noise-ratio(SNR),interferometric phase and coherence.And the height error of Spaceborne InSAR systems caused by the ionosphere is modelled.Finally,the effect of the ionosphere on the accuracy of relative height measurement is investigated based on typical parameters of P-band and L-band InSAR systems.The correction of the effects of the ionosphere on spaceborne InSAR systems is studied in Chapter 4.Firstly,to estimate the temporal difference of the ionospheric TEC(total electron content)between two passes,two methods in the literature,namely spectrum-split method and group-phase delay difference method,are expatiated on from two aspects about basic principle and realization procedure.Against the deficiency of the existing spectrum-split method,the improved spectrum-split method based on control point is proposed,and the simulation demonstrates the validity of the improved method.The main work and innovation in this dissertation is summarized in Chapter 5.Meanwhile,the futuristic work on the effects of the ionosphere on spaceborne InSAR systems is indicated.