Investigation of ionospheric TEC over China based on GNSS data

In this paper, the ionospheric total electron content (TEC) is derived from 250 Global Navigation Satellite Systems (GNSS) receivers over China. The GNSS TEC data are utilized to study the diurnal and day-to-day variability of ionosphere, ionospheric east west differences and to construct regional ionospheric map. The GNSS TEC curves clearly show sunrise and sunset enhancements in the diurnal variation. The peak value of TEC is lower in January 2015 than in May 2014. There is 2 h difference in the occurrence time of TEC maximum/minimum between May and January. Compared with the observations of Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS), the measurements from the Geostationary Earth Orbit (GEO) satellites of BeiDou Navigation Satellite System (BDS) clearly present the ionospheric day-to-day variability and east west differences in a region with small longitude differences (3.52-11.31 degrees). The east west differences in TEC are more obvious in larger longitude differences at 11:30 local time on 23 January 2015. The maximum east west difference in TEC is about 7 total electron content unit (TECU, 1 TECU =10(16) el m(-2)) in longitude difference of 11.31 degrees. Our analysis shows that the TEC for east west small longitude differences may be associated with the east west gradient of geomagnetic declination. Based on 250 GNSS stations, a regional TEC map constructed by Kriging method can well capture the main spatial structure of ionosphere in China. A comparison between TEC maps obtained by Kriging method and provided by Jet Propulsion Laboratory displays that there are large deviations in the North of China, which is mainly caused by the difference in the number of used GNSS stations. In addition, comprehensive investigation presents that GNSS has more advantages over GPS and GLONASS in the ionosphere research over China. (C) 2016 COSPAR. Published by Elsevier Ltd. All rights reserved.

本文利用中国上空250个全球导航卫星系统（GNSS）接收机获取电离层总电子含量（TEC）。利用GNSS TEC数据研究电离层的日变化和逐日变化、电离层东西差异并构建区域电离层图。GNSS TEC曲线清晰地显示出日变化中的日出和日落增强现象。2015年1月的TEC峰值低于2014年5月。5月和1月TEC最大/最小值出现的时间相差2小时。与全球定位系统（GPS）和全球导航卫星系统（GLONASS）的观测结果相比，北斗导航卫星系统（BDS）地球静止轨道（GEO）卫星的测量结果清晰地呈现出在经度差异较小（3.52 - 11.31度）区域内电离层的逐日变化和东西差异。2015年1月23日当地时间11:30，在经度差异较大时TEC的东西差异更为明显。在经度差异为11.31度时，TEC的最大东西差异约为7个总电子含量单位（TECU，1 TECU = 10¹⁶ 电子/平方米）。我们的分析表明，东西经度差异较小的TEC可能与地磁偏角的东西梯度有关。基于250个GNSS站，用克里金方法构建的区域TEC图能够很好地捕捉中国电离层的主要空间结构。克里金方法得到的TEC图与喷气推进实验室提供的TEC图对比显示，在中国北方存在较大偏差，这主要是由于所使用的GNSS站数量不同造成的。此外，综合研究表明，在中国电离层研究方面，GNSS相对于GPS和GLONASS具有更多优势。（C）2016国际空间研究委员会。由爱思唯尔有限公司出版。保留所有权利。