BeiDou Global Ionospheric delay correction Model (BDGIM): performance analysis during different levels of solar conditions

摘要

The BeiDou-3 system uses the BeiDou Global broadcast Ionospheric delay correction Model (BDGIM) to describe global vertical total electron content (VTEC) distributions and provide ionospheric delay mitigations in single-frequency positioning. The transmission of BDGIM correction parameters in the navigation message of BeiDou-3 started in mid-2015. The limited coverage of BeiDou-3 transmitted BDGIM parameters inhibits the evaluation of model performance during different levels of solar conditions. As such, we present a method to re-estimate BDGIM correction parameters and generate model parameters during the period 2010-2017 using a small global network of 20 global navigation satellite system (GNSS) stations. Tests covering the eight years demonstrate that BDGIM can reduce the ionospheric error to less than 25% for 98% of the examined samples when compared to global ionospheric maps (GIMs) provided by the International GNSS Service (IGS), and for 90% when compared to the observed VTECs from Jason-2/3 altimetry missions. Overall, BDGIM reduces residual ionospheric delays by 10-20% compared to the ionospheric correction algorithm (ICA) of the global positioning system (GPS), the empirical International Reference Ionosphere (IRI) 2016, and our fitted NeQuick-C model. The root-mean-square (RMS) error of BDGIM increases by 32 and 21% in comparison with GIM-derived and Jason-2 observed VTECs during the geomagnetic storm in March 2015, indicating the significant degradation of model performance during the disturbed geomagnetic period.