Abstract
Ionospheric delay is a crucial error source and determines the source of single-frequency precise point positioning (SF-PPP) accuracy. To meet the demands of real-time SF-PPP (RT-SF-PPP), several international global navigation satellite systems (GNSS) service (IGS) analysis centers provide real-time global ionospheric vertical total electron content (VTEC) products. However, the accuracy distribution of VTEC products is nonuniform. Proposing a refinement method is a convenient means to obtain a more accuracy and consistent VTEC product. In this study, we proposed a refinement method of a real-time ionospheric VTEC model for China and carried out experiments to validate the model effectiveness. First, based on the refinement method and the Centre National d’Études Spatiales (CNES) VTEC products, three refined real-time global ionospheric models (RRTGIMs) with one, three, and six stations in China were built via GNSS observations. Second, the slant total electron content (STEC) and Jason-3 VTEC were used as references to evaluate VTEC accuracy. Third, RT-SF-PPP was used to evaluate the accuracy in the positioning domain. Results showed that even if using only one station to refine the global ionospheric model, the refined model achieved a better performance than CNES and the Center for Orbit Determination in Europe (CODE). The refinement model with six stations was found to be the best of the three refinement models.
Highlights
In recent years, the use of global navigation satellite systems (GNSS) has gradually increased in geodesy, deformation monitoring, precision agriculture, hazard monitoring, and vehicle navigation fields [1,2,3,4]
We proposed a regional refinement method based on Centre National d’Études Spatiales (CNES) ionospheric vertical total electron content (VTEC) products for China, and evaluated the performance of primary results
Lik,j = ρij + c τi − τj + λ bik,j + Nki,j − Ionik,j + Tropij + εiL,k,j where superscript i and subscripts k and j denote specific satellites, frequencies, and receivers; Pik,j and Lik,j are the code and phase observations; ρij is the geometric distance from the satellite to the receiver; c denotes the speed of light; τi is the satellite clock error; τj is the receiver clock error; Ionik,j and Tropij are ionospheric delay and tropospheric delay; dik and dk,j are satellite and receiver code biases; bik,j is the phase biases; Nki,j is the ambiguity of the carrier phase; and εiL,k,j and εiP,k,j are the residuals of phase and code in GNSS measurements
Summary
The use of GNSS has gradually increased in geodesy, deformation monitoring, precision agriculture, hazard monitoring, and vehicle navigation fields [1,2,3,4]. Differential positioning can eliminate orbit error, clock error, receiver clock error, and weaken ionosphere and troposphere errors, becoming a widely used technology in the application of high-precision positioning [5,6]. Differential positioning is inconvenient and high-cost because it relays simultaneous observations at the reference station [3,7]. It derives centimeter to decimeter level positioning accuracy using a single receiver in support of precision orbit and clock products [3,8,9]. Consumer requirements of high precision positioning has gradually increased [4]. Real-time single-frequency PPP (RT-SF-PPP) has become a desired consumer positioning approach because it has more advantages like low-cost, low bandwidth, and no base station required when compared to real-time differential (RTD) positioning [10]
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