Study Of Ionospheric 4-D Multi-scale Tomography Based On GNSS Data

Ionospheric tomography based on Global Navigation Satellite System(GNSS)data is a kind of all-weather,large-scale technique,which has many advantages,such as low cost,simple operation,wide detection range and so on.Especially with the rapid development of GNSS including GPS,GALILEO,GLONASS,and BDS satellite system,a lot of data sources become available for ionospheric tomography.There are more satellite signals passing through the ionosphere,providing technical assurance for accessing to more accurate input data.Thus the temporal and spatial distribution of ionospheric electron density can be obtained by means of ionospheric tomography.At present,however,ionospheric tomography is only suitable for the reconstruction of large scale ionospheric structures and monitoring disturbances.Because of the uneven distribution of ground stations and incomplete projection limitations of the medium,middle to small scale ionospheric structures are very difficult to be reconstructed effectively.In order to detect the ionospheric electron density distribution at various scales,a multi resolution inversion(‘multi' in short)algorithm is developed in this study.The input data to the algorithm is selected from observations of ground stations located at the west coast of the United States and in Europe.First of all,taking the ionosphere of west coast of the United States as an example,the influence of time-window length and Empirical Orthogonal Function(EOF)selection on the multi inversion results is analyzed and the best algorithm settings for ionospheric tomography are selected.Comparing the multi inversion tomography results with the no-multi tomography results,the characteristics and advantages of multi inversion algorithm are discussed.Secondly,the impact of ground distribution on multi inversion tomography results is studied according to the comparison between tomographic results of different ground station groups in peak density and those from ionosondes in Pt Arguello and Rome respectively.Finally,the temporal and spatial variation of the ionosphere over the North American and European region during storm periods is discussed with the multi inversion method,as well as the difference between tomographic results based onGNSS data and that based on GPS data.It is observed that in the inversion region,ionospheric four-dimensional multi-scale tomographic images can be achieved with the ‘multi' algorithm,and the multi-pass inversion approach offers an improvement in accuracy.The multi algorithm can be used to construct the ionosphere model in the future,so as to detect continuous temporal and spatial variation of the ionosphere,especially imaging the ionospheic structures at middle to small scales,and provide the required performance assurance for the application of satellite navigation systems.