# A Novel Method to Mitigate the Multipath Error for BDS-2 Dam Deformation Monitoring
## 5 Conclusions  
In this study, we analyzed and assessed the MHGM method for the mitigation of multipath error at stations based on a multi-point hemispherical grid model. The hemisphere centered on each station was divided into a grid, and the multipath error at the station was estimated with the parameterization of grid points. In the process of grid point parameter estimation, DD residuals corresponding to the fixed ambiguity solution of different satellite pairs and different time periods were used as the input information to obtain the MHGM of each station. The performance of the MHGM derived from the BDS-2 deformation monitoring of reservoir was analyzed and assessed, and the effectiveness of  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Strategy**} & \multicolumn{2}{c}{**Static**} & \multicolumn{2}{c}{**Kinematic**} \\ \cline{2-5}  & **Horizontal (mm)** & **Vertical (mm)** & **Horizontal (mm)** & **Vertical (mm)** \\ \hline NO & 2.3 & 3.7 & 4.3 & 9.4 \\ SF & 1.8 & 2.6 & 3.8 & 8.6 \\ MHGM & 1.7 & 2.4 & 3.6 & 8.1 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Mean RMS of static with a 2 h interval and kinematic positioning results from DOY 51 to 55.  
the MHGM with respect to the SF model was investigated. The feasibility and effect of BDS-2 data applied in dam deformation monitoring were also analyzed.  
The results show that the MHGM can truly reflect the multipath error distribution of the reservoir dam, especially large multipath error caused by water surface reflection. This characteristic of the MHGM can be used to orientate the sources of multipath error around the station, and provides guidance to physically eliminating the influence of error sources. Based on the previous day's data modeling multipath error, the correction effect of the MHGM is better than that of the SF method. Multi-day of observation data can make the description of the MHGM more detailed. Compared with the SF method, the RMS of DD residuals was improved to a certain extent in the MHGM method, especially in the GEO/IGSO+MEO mode, where the improvement was as high as 17.0%. The performances of the MHGM method are consistent and not affected by the different orbital repeat times, which solves the \"zero mean\" assumption problem of the SF method. The MHGM method has a more obvious effect in the positioning accuracy for static with a 2 h interval and kinematic mode, which can improve by about 26.1%, 16.3% and 35.1%, 13.8% with respect to the method without multipath correction in the horizontal and vertical direction.  
Conceptualization, X.Z. and Y.L.; methodology, X.Z.; software, X.Z.; validation, Z.L., Y.W. and C.D.; formal analysis, C.D.; investigation, Z.L.; writing--original draft preparation, X.Z.; writing--review and editing, X.Z. and Y.L.; visualization, J.C. and R.F.; supervision, W.T.; project administration, W.T.; funding acquisition, X.Z., W.T. and C.D. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Key Research and Development Program of China, grant number 2017 YFB0503702; the National Natural Science Foundation of China, grant number 41804028 and 41874037; the Wuhan science and technology project, grant number 2018010401011271, and the Joint fund of Ministry of Education of China for Equipment Pre-research, grant number 6141A02022372. The data presented in this study are available on request from the author. The authors would like to acknowledge the IGS for providing the broadcast ephemeris and precise products. The authors declare no conflict of interest.