测站处GNSS多路径误差效应反演及其应用研究

针对测站观测环境变化对数据质量影响难以有效评估并削弱的问题，研究了一种可通用于各类卫星导航系统的多路径误差半天球格网点建模方法（multi-point hemispherical grid model，MHGM）。该方法能够综合利用不同GNSS（global navigation satellite system）系统的不同时期观测数据进行整体建模，显著削弱GNSS信号所受多路径误差影响，并图像化反演测站周围的多路径效应，确定信号干扰源的方位。算例的测试结果表明，在模拟的强多路径环境下，模型改正后模糊度固定时段的载波相位观测值残差的均方根误差（root mean square error，RMSE）统计值由0.983 cm降为0.318 cm，改善率高达67.7%。此外，MHGM建模结果中改正量较大的异常区域与对应测站处所架设挡板的方位相一致，能够反演出测站周围不同方向观测信号所受多路径误差影响。国际GNSS服务组织的历史观测数据在利用MHGM模型改正后，合计18年测试算例的观测值残差RMSE平均改善率达到29.5%。这对于评估测站观测环境在不同时期的变化状况，提升现有各类增强服务产品的精度和可靠性具有一定的潜在应用价值。

Inversion of GNSS Multipath Effects Around the Stations and Its Applications

  Objectives  It is difficult to effectively evaluate and weaken the impact of observation environment change on data quality. To solve the problem, this paper studies a multi-point hemispherical grid mod?el which can be applied to various satellite navigation systems.  Methods  It integrates the observations of different global navigation satellite system (GNSS) satellite pairs in different observation periods to establish a global optimal multipath model. GNSS multipath error can be estimated effectively using multi-point hemispherical grid model (MHGM), image-based inverse of multipath effect and reflect the orientation of interference sources in the observation environment around stations.  Results  To a certain extent the observation environment around stations can be modelled. The test under deliberate high multipath environment reveals that using MHGM significantly improved the root mean square error (RMSE) of the double-differ?enced carrier phase observation residuals in the period of fixed ambiguity, reducing the mean RMSE from 0.983 cm to 0.318 cm, a 67.7% improvement. In addition, the abnormal areas with large value of correction in the MHGM results is consistent with the direction of the baffle mounted at the corresponding stations. This model indicates multipath effects on GNSS carrier phase observations in different directions from the station. The test with International GNSS Service historical observations shows MHGM can effectively reflect the influence of changing multipath interference around stations on carrier phase observations, with an average improvement of 29.5% in the RMSE of residuals over the past 18 years.  Conclusions  This mod?el can be used to evaluate the changes in observation environments surrounding stations over time. It has potential application value to improve the accuracy and reliability of augmentation system products.