Real-Time Monitoring of Ionosphere VTEC Using Multi-GNSS Carrier-Phase Observations and B-Splines

Abstract

Monitoring the Vertical Total Electron Content (VTEC) of the ionosphere is important for applications ranging from navigation to detection of space weather events. Therefore, emerging efforts have been made by several analysis centers to estimate the VTEC using different approaches in real-time. Global Navigation Satellite Systems (GNSS) is a crucial technology for ionosphere modeling due to its worldwide distributed receivers, high temporal resolution, and low latency data dissemination capability. The selection of a convenient approach to extract ionosphere information from GNSS and the representation of VTEC by an appropriate mathematical model are essential factors for providing fast and accurate ionosphere products. Contrarily to the widespread phase-leveling method, which uses noisy and erroneous code measurements, the modeling concept in this paper utilizes pure carrier-phase measurements. Measurements acquired through the International GNSS Service (IGS) real-time service in Radio Technical Commission for Maritime Services format are from GPS, GLONASS, and GALILEO. The measurement biases, including the ambiguity of carrier-phase measurements, are simultaneously estimated along with VTEC model parameters. In our approach, VTEC is represented by B-spline expansions embedded into a Kalman filter. Due to their localizing feature, B-splines form a highly sparse structure in the filter measurement model. Thus, matrix operations for large-scale problems can be performed fast using sparse matrix operations, as is done in this study. The differential slant total electron content (dSTEC) analysis and the comparison with Jason-3 altimetry VTEC were performed for validation within selected periods in 2019. The dSTEC analysis shows that the quality of the generated real-time VTEC maps slightly outperforms those provided by the other IGS analysis centers.