Dai Wujiao, Shi Qiang, Cai Changsheng
Department of Surveying and Geo-informatics, Central South University, Changsha 410083, China.
Sensors (Basel). 2017 Apr 7;17(4):796. doi: 10.3390/s17040796.
The carrier phase multipath effect is one of the most significant error sources in the precise positioning of BeiDou Navigation Satellite System (BDS). We analyzed the characteristics of BDS multipath, and found the multipath errors of geostationary earth orbit (GEO) satellite signals are systematic, whereas those of inclined geosynchronous orbit (IGSO) or medium earth orbit (MEO) satellites are both systematic and random. The modified multipath mitigation methods, including sidereal filtering algorithm and multipath hemispherical map (MHM) model, were used to improve BDS dynamic deformation monitoring. The results indicate that the sidereal filtering methods can reduce the root mean square (RMS) of positioning errors in the east, north and vertical coordinate directions by 15%, 37%, 25% and 18%, 51%, 27% in the coordinate and observation domains, respectively. By contrast, the MHM method can reduce the RMS by 22%, 52% and 27% on average. In addition, the BDS multipath errors in static baseline solutions are a few centimeters in multipath-rich environments, which is different from that of Global Positioning System (GPS) multipath. Therefore, we add a parameter representing the GEO multipath error in observation equation to the adjustment model to improve the precision of BDS static baseline solutions. And the results show that the modified model can achieve an average precision improvement of 82%, 54% and 68% in the east, north and up coordinate directions, respectively.
载波相位多径效应是北斗导航卫星系统（BDS）精密定位中最重要的误差源之一。我们分析了北斗多径的特性，发现地球静止轨道（GEO）卫星信号的多径误差是系统性的，而倾斜地球同步轨道（IGSO）或中地球轨道（MEO）卫星的多径误差既有系统性的也有随机性的。采用改进的多径抑制方法，包括恒星滤波算法和多径半球图（MHM）模型，来改进北斗动态变形监测。结果表明，恒星滤波方法在坐标域和观测域中，分别可将东、北和垂直坐标方向定位误差的均方根（RMS）降低15%、37%、25%以及18%、51%、27%。相比之下，MHM方法平均可将RMS降低22%、52%和27%。此外，在多径丰富的环境中，静态基线解算中的北斗多径误差为几厘米，这与全球定位系统（GPS）多径不同。因此，我们在平差模型的观测方程中增加一个表示GEO多径误差的参数，以提高北斗静态基线解算的精度。结果表明，改进后的模型在东、北和垂直坐标方向上分别可实现平均精度提高82%、54%和68%。
