# An RTK UAV-Based Method for Radial Velocity Validation of Weather Radar
## 5 Conclusions  
The accurate measurement of weather radar radial velocity is of paramount importance for quality control and applications of radar velocity data. Traditional methods for measuring radial velocity in weather radar often involve the use of high-precision instruments for internal and external static calibration. These calibrations focus on adjusting parameters such as amplitude and phase in the receive channels. There is no method to evaluate the measurement accuracy of the moving target velocity in the actual working condition of the radar system. To address this issue, we used an RTK UAV to simulate external reference targets, proposed a method to validate the weather radar radial velocity, and experimentally verified it using the X-band radar at the Changsha Meteorological Radar Calibration Center and the DJI M300 RTK UAV. Consistent with the application scenarios of the method, we introduced the evaluation parameter optimal absolute accuracy as a complementary parameter for assessing the validation of point targets. The experimental results indicate that the optimal absolute accuracy of the radar radial velocity validation is less than 0.05 m/s. Furthermore, the result is in close agreement with the velocity measurement results of the external instrument, confirming the effectiveness of this method in accurately reflecting the quality of the weather radar velocity. Compared with the conventional absolute validation accuracy, the proposed optimal absolute accuracy evaluation parameter in this method effectively reduces the validation errors caused by the instability of UAV attitudes. Moreover, the method can be effectively applied to the procedural handling of practical radial velocity validation. The effect of the instability of the UAV on the radar velocity validation needs further quantitative study due to the limitations of the RTK system performance. (1) Influenced by the RTK system positioning frequency, data transmission, storage, etc., the UAV velocity update frequency is lower than the radar radial velocity acquisition frequency. Currently, only short-term average velocity can be compared as the instantaneous reference, and actual velocity references corresponding to each radar radial are not yet available. (2) The UAV RTK system may not operate effectively under some environmental conditions, such as harsh weather or complex terrain. This may limit the comprehensive assessment of radar validation. As RTK technology continues to improve and signal processing algorithms are optimized, future research will focus on aspects such as velocity comparisons based on high positioning frequency and the impact of sampling points and signal processing \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Validation Content**} & **Indicator** & **Result** & **Comment** \\ \hline Radial velocity measurement validation & Maximum deviation in a single frequency & Horizontal velocity measurement & \(\pm\)1.0 & \(\begin{matrix}0.04\\ -0.04\end{matrix}\) & \begin{matrix} External \\ External \\ Internal \\ \end{matrix} \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Measurements of radial velocities of instruments in and out of the radar (unit: m/s). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Velocity**} & \multicolumn{1}{c}{**Indicator**} & \multicolumn{1}{c}{**The Maximum Deviation**} & \multicolumn{1}{c}{**Difference**} & \multicolumn{1}{c}{**The Minimum Deviation**} & \multicolumn{1}{c}{**Difference**} \\ \hline +7 & 0.04 & 0 & 0.02 & \(-\)0.02 \\ \(-\)10 & 0.48 & 0.44 & 0.02 & \(-\)0.02 \\ +8 & 0.22 & 0.18 & 0.04 & 0 \\ \(-\)10 & 0.42 & 0.38 & 0.05 & 0.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Comparison of the UAV validation and instrumentation measurements (unit: m/s). algorithms on radial velocity validation. The aim is to improve the accuracy of the RTK UAV in the validation of the weather radar radial velocity. Conceptualization, Y.C. and L.L. ; methodology, Y.C., L.L., and J.Z. ; experiment, B.K. and M.Z. ; process, L.L.