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Abstract:
For the purposes of routinely providing reliable and low-latency Global Ionosphere Maps (GIMs), a method of estimating hourly updated near real-time GIM with a time latency of about 1 – 2 hours based on a 24-hour data sliding window of Global Navigation Satellite System (GNSS) near real-time observations and real-time data streams was presented. On the basis of the implementation of near real-time GIM estimation, an hourly updated GIM nowcasting method was further proposed to improve the accurate of short-term vertical total electron content (VTEC) prediction. On the other hand, as the inhomogeneous distribution of GNSS stations results in inaccurate VTECs in GIMs over areas with few or none GNSS stations, and complex and time-varying systematic biases between multi-source ionospheric observations bring difficulties for fusion modeling, an automated assimilation strategy of GNSS and IRI-2016 VTECs was proposed for GIM routine estimation. The reliability of GIMs in areas with lack of stations is enhanced by attaching Virtual Observation Stations (VOSs) based on IRI-2016 model and VOS bias parameters. The near real-time GIM behaves fairly consistent with the rapid GIMs, with a discrepancy of less than 1 TEC unit (TECu) overall. The 1-hour nowcasting is approximately 1 – 2 TECu more reliable than 1-day predicted GIM in eventful ionospheric electron density activity regions. The hourly updated near real-time and nowcasting GIMs have relatively high reliability and low time latency, and thus can better serve the (near) real-time users and offer accurate TEC background information in real-time GIM estimation.
