# Joint Use of Spaceborne Microwave Sensor Data and CYGNSS Data to Observe Tropical Cyclones
## 4 Results
### Maximum Wind Speed Measurement  
According to the processing method described in Section 3, we estimated the maximum wind speeds of Hurricane Florence from Figures 9 and 10. A comparison between the estimated maximum wind speeds of Hurricane Florence and the best track peak winds estimated by the NHC [33] is shown in Figure 12. Here, a time interpolation method was applied to the estimated maximum wind speeds to ensure that the estimated and NHC wind speeds used for the comparison were obtained at the same time.  
It can be clearly seen from Figure 12 that the maximum wind speeds of Hurricane Florence can be measured at more frequent intervals by fusing the SMAP radiometer and CYGNSS data than in the case of only fusing the CYGNSS data. Furthermore, the measured maximum wind speeds are in better agreement with the NHC best track peak wind speeds than those obtained by only fusing the CYGNSS data. A more detailed comparison between the estimated and NHC maximum wind speeds of Hurricane Florence is given in Table 2. The other nine hurricanes were analyzed in the same way as Hurricane Florence, and the results of this analysis are also listed in Table 2. Here, the root-mean-square difference (RMSD), the MAE, the correlation coefficient, and the bias were adopted to analyze the difference between the estimated and NHC maximum wind speeds of each hurricane. Note that the NHC best track peak wind speeds of all observed hurricanes can be accessed at [[https://www.nhc.noaa.gov/data/tcr/](https://www.nhc.noaa.gov/data/tcr/)]([https://www.nhc.noaa.gov/data/tcr/](https://www.nhc.noaa.gov/data/tcr/)).  
As shown in Table 2, when we compared the maximum wind speeds obtained by fusing the SMAP radiometer and CYGNSS data with the best track peak winds estimated by the NHC, we found that the MAE values ranged between 7.7 and 15.7 m/s, the RMSD values varied between 8.6 and 18 m/s, the correlation coefficients ranged between 0.1782 and 0.9877, the bias values varied between -8.5 and 4.5 m/s, and all of these were smaller than those obtained by only fusing the CYGNSS data, except for Hurricanes Dorian and Michael. This is due to the fact that Hurricanes Dorian and Michael made multiple landfalls during the observation period, and the SMAP radiometer can only measure the ocean surface wind speed, which results in a large difference between the estimated and NHC maximum wind speeds.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Hurricane** & **Observation Period** & **Observation Data** & **MAE (km)** & **SD (km)** & **Number of Samples** \\ \hline Lane & 20 to 23 August 2018 & SMAP + CYGNSS & 18.4 & 11.6 & 11 \\ \cline{2-5}  & & CYGNSS & 47.9 & 22.0 & 8 \\ \hline Rosa & 27 to 30 September 2018 & SMAP + CYGNSS & 40.5 & 18.9 & 11 \\ \cline{2-5}  & & CYGNSS & 49.2 & 27.1 & 8 \\ \hline Humberto & 16 to 19 September 2019 & SMAP + CYGNSS & 36.7 & 23.3 & 10 \\ \cline{2-5}  & & CYGNSS & 40.0 & 24.4 & 8 \\ \hline Lorenzo & 27 to 29 September 2019 & SMAP + CYGNSS & 38.5 & 20.0 & 10 \\ \cline{2-5}  & & CYGNSS & 48.7 & 25.9 & 7 \\ \hline \hline \end{tabular}
\end{table}
Table 1: _Cont._