Analysis Of Ionospheric Effects And Study Of Ionospheric Tomography Based On ALOS PALSAR Data

Low frequency synthetic aperture radar(SAR)has the ability to image a large area of scene in high spatial-temporal resolution.Meanwhile,it can also provide information about the vertical structure of the medium when penetrating forests and glaciers,so it plays an important role in monitoring forests and glaciers around the world.But at the same time,at a lower frequency,because of the existence of ionosphere,the measurement of spaceborne SAR signal is easily affected by the ionosphere,such as dispersion,small and medium-sized irregular bodies and polarization shift.In the remote sensing of the earth by L band SAR,the main factor that causes obvious propagation effect is the ionosphere.As the basis of the research work,after a general introduction of the ionosphere,this thesis introduces the theory of electromagnetic wave propagation,mainly including the characteristics of electromagnetic wave propagation in the background ionosphere and the influence analysis of irregular bodies,deduces the refractive index of the ionosphere,summarizes the models that can be used to simulate these effects,and briefly introduces the polarization principle.Then reviews the SAR imaging theory,based on one-point target,two-point targets and the real scene data obtained from the phased array L-band synthetic aperture radar(PALSAR)carried by the advanced land observation satellite(ALOS)are imaged.Next,the scintillation effect and Faraday rotation(FR)effect are studied respectively: the influence of ionospheric scintillation on SAR signal and imaging quality is systematically analyzed by means of modeling and simulation,and based on point target imaging and actual monopolarized ALOS.The correctness of theoretical analysis and modeling simulation is verified by the imaging scene of PALSAR.The formula of Faraday rotation angle(FRA)in FR effect is derived,and the estimation of FRA from the scattering matrix is studied.Next,the influence correction process of the above two effects is studied.Aiming at the scintillation effect,this thesis studies the algorithm process of---PGA and introduces the improved PGA.The simulation results show that the improved FRA is better.For the FR effect,the vertical total electron content(VTEC)is estimated by scattering matrix,based on the full polarization alos pallsar data,the simulation process is carried out and a higher accuracy VTEC map is obtained.Finally,the spatial electron density distribution information is reconstructed by using the tomographic technique.Compared with the real distribution of electron density generated by IRI software,the results show that the real distribution of electron density can be described more accurately.