TY - JOUR A1 - Erdogan, Eren A1 - Schmidt, Michael A1 - Goss, Andreas A1 - Görres, Barbara A1 - Seitz, Florian T1 - Real‐Time Monitoring of Ionosphere VTEC Using Multi‐GNSS Carrier‐Phase Observations and B‐Splines Y1 - 2021-10-11 VL - 19 IS - 10 JF - Space Weather DO - 10.1029/2021SW002858 PB - N2 - 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. N2 - Plain Language Summary: As part of the Earth's upper atmosphere, the ionosphere is coupled to the Sun and the Earth's lower atmosphere by complex electromagnetic and dynamic interactions of charged particles (electrons and ions) and neutral species. Spatio‐temporal variations of the ionosphere electron content are of particular importance for technologies utilizing electromagnetic signals such as navigation and telecommunication since the electromagnetic waves are refracted/reflected while traveling through the ionosphere. There has been an increasing demand for real‐time ionosphere products to compute interactions between electromagnetic waves and the ionosphere in real‐time. In this context, the IGS and its several analysis centers have been developing models to provide global Vertical Electron Content (VTEC) products using different approaches based on Global Navigation Satellite Systems (GNSS) observations. By considering the crucial impact of the ionosphere and its constituents on our life, in this study, we model the ionosphere VTEC represented by B‐splines embedded into a Kalman filter in real‐time using carrier‐phase observations from geodetic GNSS receivers. N2 - Key Points: A new real‐time approach estimating simultaneously coefficients of the B‐spline representation and biases of carrier‐phases was introduced. Carrier‐phase observations from GPS, GLONASS, and GALILEO were incorporated into an adaptive Kalman filter. Global Navigation Satellite Systems (GNSS) observations were obtained in Radio Technical Commission for Maritime Services format via the International GNSS Service real‐time service. UR - http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/9881 ER -