单站区域电离层TEC建模及精度分析

Regional Ionospheric TEC Modeling and Accuracy Analysis Based on Observations from a Station

为了分析单站区域电离层总电子含量(total electron content, TEC)模型的适用范围和精度,基于2~15阶次球谐函数,分别建立了欧洲区域16个单站区域电离层TEC模型,生成了区域格网TEC,并与欧洲定轨中心(Center for Orbit Determination in Europe,CODE)、国际全球导航卫星系统服务组织(International Global Navigation Satellite System Service, IGS)和全球GNSS监测评估系统(International GNSS Monitoring and Assessment System, iGMAS)等全球电离层产品比较分析。结果表明,基于低阶(2×2阶或3×3阶)球谐函数建立的单站区域电离层TEC模型,以单站为中心,在经纬度10°×10°范围以内(半径小于600 km),电离层TEC精度与CODE、iGMAS和IGS等全球电离层产品的TEC精度相当,约为1.0 TECU,实现了在一定区域内(半径小于600 km)利用单站建立电离层TEC模型替代全球电离层TEC模型,高效地为区域内单频用户提供高精度的电离层延迟改正。

Objectives:Establishing a regional ionospheric total electron content(TEC) model from a single station is much more efficient than developing a global multistation model because of its small amount of data. However, the single-station regional ionospheric TEC model has a scope of application. Therefore, the study of the scope and accuracy of a single-station regional ionospheric TEC model can effectively provide high-precision ionospheric delay correction for single-frequency users in the region. Methods:With 2-to15-order spherical harmonic functions, single-station regional ionospheric TEC models are established using global navigation satellite systems(GNSS) observations from 16 stations in the European region during day of year(DOY) 357—363 in 2017, a period of calm solar activity and without a magnetic storm. The average ionospheric TEC values and average root mean square(RMS) values at all grid points in the longitude–latitude ranges of 0°×0°, 10°×5°, 10°×10°, 10°×15°, 20°×15°, and 20°×20° are compared with those of global ionospheric products such as Center for Orbit Determination in Europe(CODE), International GNSS Monitoring and Assessment System(iGMAS), and International GNSS Service(IGS) for the determination of the scope of application and accuracy of the single-station regional ionospheric TEC models.Results:(1) The 16 single-station regional ionospheric TEC models based on 2-to-15-order spherical harmonic functions have the average TEC values within the value range of CODE, iGMAS, and IGS in different regions. In other words, within the latitude-longitude range of 20°×20°, the TEC values of the single-station regional ionospheric models established by the proposed method are comparable to those of CODE, iGMAS, and IGS.(2) The RMS values of regional ionospheric TEC models established with the data of 16 single stations and 2-to-15-order spherical harmonic functions are different from those of IGS beyond the latitude-longitude range of 10°×10°. The lower order of spherical harmonic functions in the latitude-longitude range of 10°×10° corresponds to smaller RMS values of the models. The accuracy of the single-station regional ionospheric TEC models based on low-order(2×2 or 3×3) spherical harmonic functions is similar to that of IGS in the 10°×10° range centered on a single station, namely that the applicable radius of the single-station regional ionospheric TEC models is about 600 km and the accuracy is about 1 TECU.(3)The single-station regional ionospheric TEC models are highly consistent with the IGS global ionospheric TEC model, which indicates that the accuracy of the single-station regional ionospheric TEC models based on low-order(2×2 or 3×3) spherical harmonic functions is comparable to that of the IGS global ionospheric TEC model.Conclusions:The results show that the single-station regional ionospheric TEC models based on low-order(2×2 or 3×3) spherical harmonic functions has the comparable accuracy to that of global ionospheric products such as CODE, iGMAS, and IGS, which is about 1.0 TECU, within the latitude-longitude range of 10°×10°(radius < 600 km) centered on a single station. Thus, the global ionospheric TEC model can be replaced by the ionospheric TEC model established with data of a single station in a certain region(radius less than 600 km), with which the high-precision ionospheric delay correction can be efficiently provided for single-frequency users in the region.