Network-based real-time kinematic ionospheric residual modelling and integrity monitoring system

Abstract

The Earth’s ionosphere, which is among the major error contributor in Global Positioning System (GPS), is sensitive to level of solar activities. During this study, the concern is on the peak of upcoming Solar Cycle 24 expected in May 2013, which will induce severe disturbance to the ionosphere. This phenomenon raises the question of how will this affect the equatorial ionosphere and real-time GPS positioning. This research helps to understand the geomorphology and climatology of equatorial ionosphere in the Malaysian sector. A combination of local and global GPS network with abundant data has been employed to map the Total Electron Content (TEC) of equatorial ionosphere over Malaysia. The results show that dynamic morphological characteristics of ionosphere induce spatially- and temporally-correlated errors to GPS positioning. A significant amount of these effects can be mitigated with Network-based Real-Time Kinematic (NRTK) technique by generating network correction. This network correction can be tuned to output dispersive correction in order to better model the ionospheric residuals. Dispersive correction approach has been implemented in ISKANDARnet NRTK system for NRTK service enhancement. Extensive tests conducted within ISKANDARnet coverage under undisturbed ionosphere condition found that dispersive correction approach outperformed conventional lump correction with: (i) mean improvement of 20% in ambiguity resolution success rate, (ii) positioning accuracy was two-fold better with all error components lay within ±10 cm, and (iii) 21% improvement in mean ambiguity resolution validation ratio was achieved. However, imperfect ionospheric modelling due to rapid ionospheric irregularities leads to the need of establishing a near real-time ionospheric outburst monitoring system. Thus, the ISKANDARnet Ionospheric Outburst MOnitoring and Alert System (IOMOS) is developed to effectively quantify ionospheric disturbances, translate into indices and disseminate nowcast alert to users in near real-time. The IOMOS mainly serves as NRTK integrity monitoring system to ensure reliable NRTK solutions are delivered to users. It also functions as a near real-time space weather monitoring system to probe ionospheric perturbations. Overall, this research will ultimately benefit the GPS positioning and space weather communities.