Performance and Analysis of Ionospheric Enhanced PPP-RTK in Different Latitudes
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摘要: 收敛速度慢一直是限制精密单点定位（precise point positioning，PPP）发展的重要因素。研究表明，通过高精度电离层延迟改正，进而实现PPP-RTK （real-time kinematic），可显著提升PPP的收敛速度。目前区域PPP-RTK中电离层主要采用单星多项式电离层模型（satellite-based ionospheric model with POLYnomial function，SIM_POLY）与反距离内插模型（satellite-based ionospheric model with inverse distance weight function，SIM_IDW）进行建模。为了验证上述两种模型在不同纬度的建模精度，对广东、湖北及河北三地上空电离层延迟进行建模，并将其应用于单/双系统、浮点解及固定解中，分析其定位性能。实验结果表明，低纬地区，SIM_IDW模型表现略优于SIM_POLY，中高纬地区则并无显著差异。浮点解PPP中，与无电离层组合（ionosphere-free PPP，IFPPP）及CODG（centre for orbit determinationin europe global ionospheric map，CODE GIM）电离层产品改正下的非差非组合结果进行比较，河北地区与广东及湖北地区相比收敛速度最快，单GPS解算模式下定位精度相较于IFPPP分别提升了43.7％和43.0％。固定解PPP中，河北地区GPS+北斗解算模式下，SIM_IDW、SIM_POLY模型改正下的PPP-RTK首个历元模糊度固定成功率可达86.09%和89.13%，且水平方向首个历元收敛至5 cm，高程方向1.5 min内收敛至10 cm；定位精度方面，在引入北斗系统之后，双系统PPP-RTK相较于单GPS在定位性能方面有明显提升，河北地区GPS+北斗解算模式下，SIM_IDW、SIM_POLY模型改正下的PPP-RTK水平及三维定位精度为1.3cm及3.5 cm。通过SIM_IDW及SIM_POLY模型建立区域电离层模型进而实现PPP-RTK，可以显著缩短PPP收敛时间，提高定位精度。Abstract: Objectives: Slow convergence has always been an important factor of limiting the development of precise point positioning (PPP). Studies have shown that the convergence speed of PPP can be significantly improved with high-precision ionospheric delay correction, and then to achieve PPP-RTK. At present, the ionosphere in the regional PPP-RTK mainly adopts the satellite-based ionospheric model with polynomial function (SIM_POLY) and the satellite-based ionospheric model with inverse distance weight function (SIM_IDW) for construction. Methods: In order to verify the modeling accuracy of the above two models at different latitudes, this paper first used the observation data of Guangdong, Hubei and Hebei to establish ionospheric delay models over Guangdong, Hubei and Hebei regions. Then applied the above models to float and fixed PPP under single GPS and GPS+BDS. And finally compared the above results with IFPPP (ionosphere-free PPP) and CODG (centre for orbit determination in europe global ionospheric map) correction. Results: Experimental results show that in the low-latitude regions, SIM_IDW slightly outperformed SIM_POLY, but there was no significant difference in the middle and high latitude regions. Compared with IFPPP and CODG correction in the float PPP, Hebei achieved the fastest convergence speed compared with Guangdong and Hubei, and the positioning accuracy in single GPS solution is improved by 43.7% and 43.0% compared with IFPPP, respectively. In the fixed PPP, the success rate of first epoch to fix the ambiguity of PPP-RTK under the correction of SIM_IDW and SIM_POLY models in GPS+BDS solution could reach 86.09% and 89.13% in Hebei area. Besides, it could converge to 5 cm in the first epoch in horizontal, and converged to 10 cm within 1.5 minutes in vertical, and the accuracy of GPS+BDS PPP-RTK had a significant improvement in positioning compared with single GPS, which was 1.3 cm in horizontal and 3.5 cm in three-dimensional under the correction of SIM_IDW and SIM_POLY models, respectively. Conclusions: Establishing a regional ionospheric model through SIM_IDW and SIM_POLY models to realize PPP-RTK can significantly shorten the PPP convergence time and improve positioning accuracy.
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Key words:
- PPP /
- PPP-RTK /
- un-differenced and un-combined /
- Ionospheric model /
- multi-system PPP
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