Abstract
As one significant component of space environmental weather, the ionosphere has to be monitored using Global Positioning System (GPS) receivers for the Ground-Based Augmentation System (GBAS). This is because an ionospheric anomaly can pose a potential threat for GBAS to support safety-critical services. The traditional code-carrier divergence (CCD) methods, which have been widely used to detect the variants of the ionospheric gradient for GBAS, adopt a linear time-invariant low-pass filter to suppress the effect of high frequency noise on the detection of the ionospheric anomaly. However, there is a counterbalance between response time and estimation accuracy due to the fixed time constants. In order to release the limitation, a two-step approach (TSA) is proposed by integrating the cascaded linear time-invariant low-pass filters with the adaptive Kalman filter to detect the ionospheric gradient anomaly. The performance of the proposed method is tested by using simulated and real-world data, respectively. The simulation results show that the TSA can detect ionospheric gradient anomalies quickly, even when the noise is severer. Compared to the traditional CCD methods, the experiments from real-world GPS data indicate that the average estimation accuracy of the ionospheric gradient improves by more than 31.3%, and the average response time to the ionospheric gradient at a rate of 0.018 m/s improves by more than 59.3%, which demonstrates the ability of TSA to detect a small ionospheric gradient more rapidly.
Highlights
As one significant component of space environmental weather, the ionosphere is one of the critical error sources for a diversity of applications using satellite navigation, e.g., farming, construction, exploration, surveying and civil aviation [1]
Compared to the traditional code-carrier divergence (CCD) methods, the experiments from real-world Global Positioning System (GPS) data indicate that the average estimation accuracy of the ionospheric gradient improves by more than 31.3%, and the average response time to the ionospheric gradient at a rate of 0.018 m/s improves by more than 59.3%, which demonstrates the ability of two-step approach (TSA) to detect a small ionospheric gradient more rapidly
To further assess the proposed ionospheric anomaly monitoring approach, which is superior to traditional CCD methods on both response time to ionospheric gradient anomaly and the estimation accuracy of ionospheric gradient, the real-world GPS data are collected at Beijing University of Civil
Summary
As one significant component of space environmental weather, the ionosphere is one of the critical error sources for a diversity of applications using satellite navigation, e.g., farming, construction, exploration, surveying and civil aviation [1]. Theintroduced positioning accuracy bypseudorange the single-frequency smootheddue pseudorange in normalaffects conditions, the ionospheric gradient, which is a dominant threat for GBAS while duringleading the ionosphere satellite signal propagation by lagging code measurements ionosphere storm events, namely will be introduced into the smoothed (CCD). In GBAS, order to ensure the integrity of code-based differential positioning technique in gradient and response time to the ionospheric gradient anomaly simultaneously, namely CCD. For the purpose of meeting the Minimal Operational Performance Standards (MOPS) requirements on the ionospheric gradient anomaly for LAAS [18,19], a geometric moving averaging (GMA) method of a linear time-invariant first-order low-pass filter (called CCD-1OF) is used to consider both the estimate accuracy of the ionospheric gradient and the response time to the ionospheric gradient anomaly, as the recommended integrity monitoring algorithm of LAAS [20].
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