Retrieving Vertical Electron Density (VED) Profile with Combined Tomography and Abel Inversion Techniques

When electrical magnetic wave passes through the ionosphere, it is reflected and disturbed. This feature will bring: 1) beneficial results i.e. as a media for radio signal long distance propagation; and 2) disadvantage results i.e. causing Global Positioning System (GPS) inaccuracy. Therefore it is necessary to build up an accurate ionospheric model for use in various applications. Because electron density is the most important parameter of the ionosphere, the researchers have put a great effort to investigate the temporal and spatial distributions of the electron density. Although many progresses have been made, exact vertical electron density (VED) profile retrieve is still a challenging issue because of the ionospheric instability and the lack of efficient instruments and mathematical models. Nowadays, Abel inversion and tomographic technology are two effective methods to retrieve VED. Each of them has its advantage. The Abel inversion uses less observed data but the result is not accurate. The tomographic technology is more accurate but a large number of initial data and observed data need to be used. In this paper, the Abel inversion and tomography ART (Algebraic Reconstruction Technique) algorithms are combined together to generate the local VED profile. This proposed method has higher accuracy although it is achieved only by small amount of observed data. Moreover, a wide area VED profile also can be generated through combining the retrieved local VED profiles. Therefore, the proposed method can well utilize the advantages of the Abel inversion and the tomographic technology. This proposed modeling process includes three steps: 1) the prior data, such as the tomography ART model initial values, firstly are generated. Such prior data are a VED profile which is generated by the RO (radio occultation) data using the Abel inversion algorithm. The retrieved VED is only the function of the altitude; 2) a set of the VED profiles, which are the function of altitude and zenith angle, are retrieved based on the ground based GPS observation data. These VED profiles is generated based on the ART algorithm and using the prior data from step one as the initial input data; 3) combining all the retrieved VED profiles from step two, a local area VED profile with altitude and zenith angle parameters is then generated by the splint interpolation algorithm. In the final part of the paper, the validation of this technique is also discussed based on the data comparison among the propose model, the ionosonde, the Abel inversion model and the NeQuick model.