Real Time PPP Solution Method Considering Tropospheric Anisotropy

Objectives: Tropospheric anisotropy is one of the important factors affecting the positioning accuracy of Global Navigation Satellite Systems (GNSS). The existing Real Time Precision Point Position (RT-PPP) technology usually combines empirical models, projection functions, and parameter estimation methods to eliminate the influence of tropospheric delay, but does not consider the impact of tropospheric anisotropy on positioning results. Solar radiation is an important factor causing tropospheric anisotropy. Therefore, this paper proposes an RT-PPP calculation method that takes into account the tropospheric anisotropy caused by solar radiation. Methods: This article calculates the solar altitude angle based on the station position and local time, characterizes the influence of solar radiation on GNSS signals, and improves the existing wet projection function and stochastic model to construct RT-PPP function model and stochastic model that consider the anisotropy of the troposphere. The method proposed in this paper is validated by selecting 7 days of multimodal global navigation satellite system (Multimodal Global Navigation Satellite System, Multi GNSS) observation data from 13 International GNSS Service (IGS) center stations distributed globally, with an annual area of 64-70 days. Results: The RT-PPP positioning method proposed in this article, which takes into account the anisotropy of the troposphere, outperforms traditional methods and improves positioning accuracy in the N, E, and U directions to some extent. In terms of convergence time, the improvement rates of convergence speed in the three directions are 1.45%, 0.93%, and 2.67%, respectively. Through analysis of stations at different latitudes, it was found that the method proposed in this paper has improved the positioning results and convergence speed of stations in different latitude intervals to a certain extent, indicating that the method proposed in this paper has a certain degree of robustness. Conclusions: The method proposed in this article considers the impact of solar radiation on satellite signals passing through the troposphere, filling the gap in the influence of tropospheric anisotropy on RT-PPP. It is of great significance for further improving the theory and methods of RT-PPP that take into account tropospheric anisotropy.