摘要:
对流层各向异性是影响全球导航卫星系统（ Global Navigation SatelliteSystem，GNSS）定位精度的重要因素之一，现有的实时精密单点定位（Real TimePrecise Point Position，RT-PPP）技术通常联合经验模型、投影函数和参数估计法消除对流层延迟影响，但并未考虑对流层各向异性对定位结果的影响。太阳辐射是导致对流层各向异性的重要因素，因此，本文提出一种顾及太阳辐射导致对流层各向异性的RT-PPP解算方法，该方法基于测站位置和地方时计算太阳高度角，表征太阳辐射对GNSS信号的影响，并对现有湿投影函数及随机模型改进，构建顾及对流层各向异性的RT-PPP函数模型和随机模型。选取全球分布的13个国际GNSS服务（International GNSS Service，IGS）中心站年积日64-70共7天的多模式全球导航卫星系统（Multimodal Global Navigation Satellite System，multiGNSS）观测数据对本文提出的方法进行验证，实验结果表明，本文提出的顾及对流层各向异性的RT-PPP定位方法优于传统方法，在N、E、U三个方向上定位精度均有一定的改善。在收敛时间方面，三个方向上收敛速度的改善率分别为1.45%、0.93%和2.67%。对不同纬度测站进行分析，发现本文提出方法在不同纬度区间内测站的定位结果和收敛速度均有一定程度的改善，说明本文提出方法具有一定的鲁棒性，对进一步完善顾及对流层各向异性的RT-PPP理论与方法具有重要意义。
Abstract:
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.
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