# Experimental Study of Accuracy of High-Rate GNSS in Context of Structural Health Monitoring
## 4 Conclusions  
We have systematically assessed the performance of high-rate GNSS position observations computed with PPP, PPP-AR, and RTK techniques in monitoring structural deformation and dynamics based on a set of controlled experiments carried out in Hong Kong. When high-rate positioning was carried out, the RTK technique with observations from all the available GNSS offered the best accuracy among the tested positioning techniques and different combinations of satellite systems, followed by PPP-AR, which could potentially be an alternative approach to the commonly used RTK technique for millimeter-level SHM applications. The standard deviations of the 100 Hz GNSS displace  
Figure 14: Comparison between 100-Hz, 10-Hz, and 1-Hz GNSS time series (red dots) and laser displacement transducer (yellow dots) for the third sinusoidal motion. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sampling Rate** & **PPP** & **PPP-AR** & **RTK** \\ \hline
1-Hz & 16.34 & 6.06 & 4.66 \\
10-Hz & 17.18 (5.1\%) & 6.58 (8.6\%) & 4.79 (2.8\%) \\
100-Hz & 17.96 (9.9\%) & 7.01 (15.6\%) & 4.91 (5.4\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: RMSE of 100-, 10-, and 1-Hz displacement time series derived with PPP, PPP-AR, and RTK techniques (in mm). The values in the brackets are the percentage increases compared to the 1-Hz standard deviations. ment solutions derived from PPP, PPP-AR, and RTK techniques were 5.5 mm, 3.6 mm, and 0.8 mm, respectively, when the antenna was in quasi-static motion, and were about 9.2 mm, 6.2 mm, and 3.5 mm, respectively, when the antenna was in vibration (up to about 0.7 Hz), under typical urban observational conditions in Hong Kong. We have also shown that the higher a sampling rate was, the lower the accuracy of a measured displacement series was. On average, the 10 Hz and 100 Hz results were 5.5% and 10.3% noisier than the 1 Hz results, respectively. However, since the high-rate data series offered more detailed displacement information, it is still critical to deploy the high-rate systems to monitor highly dynamic civil infrastructures despite the lower accuracy. Conceptualization, X.Q. and B.S. : data curation, X.Q., B.S. and Y.L. : formal analysis, X.Q., B.S. and X.D. : funding acquisition, X.D. and L.W. : investigation, X.Q. and Y.L. : methodology, X.Q. and B.S. : project administration, X.D. and L.W. : resources, Y.L. ; software, B.S. : supervision, X.D. and L.W. : validation, X.D., G.L. and L.W. : visualization, Y.L. ; writing - original draft, X.Q. : writing--review and editing, B.S. and X.D. All authors have read and agreed to the published version of the manuscript. The research was jointly supported by the National Key R&D Program of China (2021 YFC3000501) and the National Natural Science Foundation of China (42004024; 41877289) and the Research Grants Council (RGC) of the Hong Kong Special Administrative Region (PolyU 152164/18E and PolyU 152233/19E). The phase-bias products can be obtained from [[ftp://igs.gnsswhu.cn/pub/whu/phasebias](ftp://igs.gnsswhu.cn/pub/whu/phasebias)]([ftp://igs.gnsswhu.cn/pub/whu/phasebias](ftp://igs.gnsswhu.cn/pub/whu/phasebias)). The precise products of GFZ can be obtained from [[ftp://ftp.gfz-potsdam.de](ftp://ftp.gfz-potsdam.de)]([ftp://ftp.gfz-potsdam.de](ftp://ftp.gfz-potsdam.de)). The first author is grateful to the Chinese National Rail Transit Electrification and Automation Engineering Technology Research Centre (Hong Kong Branch) for the PhD studentship provided. The authors thank the Wuhan University and IGS centers for providing the precise GNSS products for this study. We would also like to thank [PERSON] of the Shanghai Observatory of the Chinese Academy of Sciences, author of the Net_Diff software, for making the Net_Diff software available. The authors declare no conflict of interest. Figure A2: Satellite number (top) and Position Dilution of Precision (PDOP, bottom) during the experiment.