非差非组合PPP的广域星间单差天顶电离层模型及其验证

Wide-Area Between-Satellite Single-Difference VTEC Ionospheric Model and Its Assessment for Undifferenced and Uncombined PPP

    摘要
  • 摘要: 高精度电离层修正是非差非组合精密单点定位（precise point positioning, PPP）加速收敛的重要前提。首先基于参考站网台站观测数据, 以非差非组合精密单点定位提取的电离层延迟作为建模数据源，提出一种基于多项式模型的估计天顶电离层延迟参数以及卫星硬件延迟的单差电离层模型。然后开发了服务端和用户端相应软件系统，服务端提取电离层延迟和进行单差建模，并将模型参数播发给用户端作为电离层约束进行非差非组合精密单点定位。最后在欧洲地区通过PPP提取电离层进行拟合实验，结果表明，广域地区GPS和俄罗斯GLONASS（global navigation satellite system）单系统电离层模型内外符合精度分别为1 TECu（total electron content unit）和3 TECu。采用电离层约束的非差非组合动态精密单点定位，统计136个1 h时段的定位结果，发现在附加电离层约束PPP实验中，78个时段（57.35%）收敛时间在5 min内，97个时段（71.32%）在10 min内，122个时段（89.7%）在15 min内，132个时段（97.06%）在25 min内；在无约束PPP实验中，上述收敛时间内结果分别为15个（11.03%）、64个（47.06%）、91个（66.91%）、110个（80.88%）。

     

    Abstract:
      Objectives  High-precision ionospheric correction is an important prerequisite for undifferenced and uncombined precise point positioning (PPP) with fast convergence capability. Different from the traditional use of pseudoranges to extract ionospheric information, the ionospheric accuracy obtained by PPP with fixed ambiguity is higher.
      Methods  A wide-area vertical total electron content(VTEC) ionospheric model is developed based on a reference network, where the VTEC of each station is extracted from the undifferenced and uncombined PPP approach. The proposed VTEC model is expressed in the between-satellite single-differenced polynomial function of the sites' latitude and solar hour angle. A data processing procedure and software system are developed for both processing server and user PPP client. In the server part, the VTEC ionospheric delay of the whole network is estimated, the VTEC polynomial function is established and the model parameters are broadcasted to the PPP clients. In the user PPP client, real-time positioning using the broadcasted wide-area VTEC parameters are performed.
      Results  Experiments using the GNSS network in the European region are performed, and results show that the internal RMSE(root mean squared error)and external RMSE of the derived VTEC model is around 3 TECus and 1 TECu for the GLONASS(global navigation satellite system) and GPS, respectively. User kinematic PPP test results using the new VTEC ionospheric model show that, 78 of the whole 136 (57.35%) kinematic undifferenced and uncombined PPP hourly samples converge in 5 minutes, where for 97 samples (71.32%) converge in 10 minutes, 122 samples(89.7%)converge in 15 minutes and 132 samples(97.06%)converge without 25 minutes. In the unconstrained PPP experiment, the results in the above convergence time are 15 (11.03%), 64 (47.06%), 91 (66.91%), and 110 (80.88%), respectively.
      Conclusions  Experiments show that single-difference VTEC ionospheric model has a huge improvement in the accuracy of extracting the ionosphere and shortening the real-time PPP convergence time in a wide-area.

     

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