Study And Application Of Ionospheric Tomography Algorithms With Smoothing Constraints

High-accurate three-dimensional structure of ionospheric electron density has vital scientific significance and application value for calculating reliable ionospheric delay parameter,researching spatial-temporal variability of ionosphere and anomalous characteristics,as well as providing effective data reference for the forcast and warning of space-weather and geoscience disastrous events.Due to such advantages as long detecting time,wide range and low cost,computerized ionospheric tomography(CIT)using GNSS observations become a important method to monitor and model ionosphere.Because of limited observation angle of view and uneven distribution of observation stations,in the process of the construction of ionospheric electron density inversion,the ill-posed problem,that the resolution of non-uniqueness or instability,would be caused.Taking these problems into consideration,the research work mainly focused on the following several aspects:(1)The paper takes Fitting Method by Selection of the Parameter Weights into ionospheric electron density inversion.In this method,choosing proper constraint conditions to construct parameter weights matrix is equal to add the observation information via normal equations.The result shows that using this method,the ill-posed problem of ionospheric tomography system is efficiently resolved.And the feasibility and superiority of the algorithm are validated by numerical simulation and factual observations.(2)The FMSPW is direct algorithm.When improving the spatial resolution,large matrix need to be manipulated in this algorithm to decrease computational deficiency and increase the condition number of normal equation set.On the basis of Adaptive Simultaneous Algebraic Reconstruction Technique,Gaussian-like weight according to distance is introduced to smooth neighbor voxels.This paper pretent a new algorithm,named Constraint Adaptive Simultaneous Algebraic Reconstruction Technique by Gaussian-like weight,which overcome the defect that voxels without rays depend on initialized value,and whose precision is improved efficiently.At last,numerical simulation and factual observations validate the feasibility and superiority of the algorithm.(3)Considered that the constraints of above algorithms are based on partial smooth assumption to reflect ionospheric physical state in quiet geomagnetic condition,ionospheric TEC using GNSS and geomagnetic data observed by geomagnetic observatory in China and the surrounding have been used to analyze the morphological response of TEC and its physical origin during super geomagnetic storm in October and August 2003.And the result shows the correspondence between the change rate of TEC and horizontal component of the geomagnetic field in the south and north of China.In addition,according to the above results,preliminary analysis on the physical mechanism has made for the establishment of ionospheric tomography algorithm in magnetic storm conditions.