Independent temporal and spatial variation analysis of ionospheric TEC over Asia-Pacific area based on BDS GEO satellites

Abstract

GPS has been widely used to monitor ionospheric total electron content (TEC) variations. However, GPS-derived TEC contains ionospheric horizontal gradient information due to the motion of GPS satellites. As a result, the temporal and spatial variation information is mixed. With the advent of the geostationary earth orbit (GEO) of the BeiDou navigation satellite system (BDS), observations from BDS GEO satellites provide a new opportunity for independent research on the temporal and spatial variations of the ionospheric TEC. Furthermore, the GEO satellite also enables continuous and long-term TEC monitoring. Due to its higher orbit, the BDS GEO-derived TEC also contains more plasmaspheric electron content. In this study, the temporal and spatial variation characteristics of the ionospheric TEC derived from the BDS GEO satellites over the Asia-Pacific area are investigated. The achievable TEC theoretical accuracy from the BDS GEO measurements is first deduced. The TEC time series at 26 BDS stations over the Asia-Pacific area is then analyzed. Results acquired from the vertical TEC (VTEC) observations in 2017 indicate obvious periodic variations and spatial variations with a semi-annual anomaly. Through an analysis of the VTEC series over a span of five years, it is revealed that the long-term TEC variations are quite dependent on the solar activity intensity in terms of the F10.7 index. Besides, the BDS GEO-derived VTEC variation trend is consistent with those acquired from the global ionospheric map (GIM) and the NeQuick model. However, significant biases exist at some stations due to uneven accuracy of the two global ionospheric models. The maximum RMS discrepancies reach 4.3 TECU and 9.9 TECU for the GIM and NeQuick, respectively.