北斗卫星伪距多路径系统偏差的修正方法及其对单频PPP的影响分析

北斗伪距观测值存在特有的多路径系统性偏差,偏差的数量级达到几个分米到米。该系统偏差可分为两类:一类是IGSO/MEO卫星随高度角变化的伪距系统性偏差;另一类是GEO卫星(高度角仅微小变化)明显的伪距系统性偏差。系统性的伪距偏差导致GEO卫星MP序列的标准偏差较大,本文针对GEO卫星伪距偏差问题提出了一种基于卡尔曼滤波的修正方法,修正后的GEO卫星MP序列的标准偏差下降了10%~16%。基于伪距相位组合的单频PPP技术的伪距权重较大,会受到北斗伪距偏差的影响,分析表明该系统性偏差将导致单频PPP定位结果高程方向产生约1m的偏差。对GEO伪距偏差采用提出的卡尔曼滤波修正方法进行修正,并应用Wanninger和Beer的高度角模型消除IGSO/MEO观测值伪距偏差,本文对修正后的单频精密单点定位精度进行了分析。4个multi-GNSS experiment(MGEX)站10d观测数据的分析结果表明:仅改正和卫星多路径误差,高程方向定位结果精度可改善65%左右;采用本文方法对GEO卫星的多路径修正后,该方向定位结果精度改善比例将进一步提高至75%左右。

Correction Model of BeiDou Code Systematic Multipath Errors and Its Impacts on Single-frequency PPP

There are systematic multipath errors on BeiDou code measurements, which are range from several decimeters to larger than 1 meter.They can be divided into two categories, which are systematic variances in IGSO/MEO code measurement and in GEO code measurement.In this contribution, a methodology of correcting BeiDou GEO code multipath is proposed base on Kalman filter algorithm.The standard deviation of GEO MP Series decreases about 10%~16% after correction.The weight of code in single-frequency PPP is great, therefore, code systematic multipath errors have impact on single-frequency PPP.Our analysis indicate that about 1 m bias will be caused by these systematic errors.Then, we evaluated the improvement of single-frequency PPP accuracy after code multipath correction.The systematic errors of GEO code measurements are corrected by applying our proposed Kalman filter method.The systematic errors of IGSO and MEO code measurements are corrected by applying elevation-dependent model proposed by Wanninger and Beer.Ten days observations of four MGEX (Multi-GNSS Experiment) stations are processed.The results indicate that the single-frequency PPP accuracy can be improved remarkably by applying code multipath correction.The accuracy in up direction can be improved by 65% after IGSO and MEO code multipath correction.By applying GEO code multipath correction, the accuracy in up direction can be further improved by 15%.