# Study on the Elimination Method of Wind Field Influence in Retrieving a Sea Surface Current Field
## 6 Results and Analysis
### Accuracy Analysis  
The retrieval current of images (c) and (d) in Figure 7 was compared with the HFSWR data, because SAR and HFSWR have the same coverage area, as shown in Figure 1. The results are given in Table 4.  
The regression coefficients were 0.3931 and 0.5861, respectively, indicating that the retrieved current had a linear relationship with the HFSWR data. It should be noted that the HFSWR is an average result for a sampling interval of 20 min, while SAR is a transient result. Therefore, there are some differences between them, and the correlation is not so strong. In contrast, the current field obtained using wind field correction based on SAR  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Result** & **Image (b)** & **Image (c)** \\ \hline Correlation Coefficient & 0.4412 & 0.0129 \\ Mean Difference & 0.0480 & 0.0307 \\ RMSE & 0.2768 & 0.1495 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Measured currents processed with the retrieved wind field, and a comparison with GF\(-\)3 and HFSWR.  
Figure 11: Results of retrieving the ocean surface currents. (**a-e**) are retrieving the ocean surface currents from the five scenes in the Figure 1.  
retrieval is closer to the result obtained by the shore-based radar than that obtained using ECMWF correction.  
As Table 4 shows, for image (b) and image (c), the correlation coefficients between the retrieved current data and the retrieved wind field and the HFSWR data are 0.4412 and 0.0129, respectively. In Table 5, for image (b) and image (c), the correlation coefficients between the retrieved current data with the ECWMF wind field and the HFSWR data are 0.4593 and 0.0191, respectively. The mean difference between the retrieved current and the HFSWR-derived current is 0.048 m/s and 0.0307 m/s, while the RMSE is 0.2768 m/s and 0.1495 m/s, respectively. In contrast to Table 4, the mean difference between the retrieving current and the HFSWR-derived currents is 0.3047 m/s and 0.3855 m/s, while the RMSE is 0.4161 m/s and 0.4141 m/s in Table 5. Through comparison of the above results, it can be seen that for the same image, the RMSE in Table 4 is smaller, so the corresponding result is better.  
In addition, the consistency of the two results was also investigated. Figure 12 shows the statistical results of the retrieved current, with the retrieved wind field versus the HFSWR data; Figure 13 shows the statistical results of the retrieved current with the ECMWF field versus the HFSWR data. Obviously, there is a good general agreement between the retrieved current and the retrieved wind field and the HFSWR data.  
Additionally, for the ECMWF wind field, the CDOP model was used to correct the interference term in the ATI Doppler velocity, and the ocean surface current field was obtained. Scatter diagrams and the statistical results are shown in Figure 13. Compared with Figure 13, the result of currents processed with the retrieved wind field was better than that obtained using the ECMWF reanalysis wind field.  
Figure 12: Scatter diagrams of the GF\(-\)3 ATI currents processed with the retrieved wind field versus the HFSWR data for the two scenes: (**a**) represents scene b; (**b**) represents scene c.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Result** & **Image (b)** & **Image (c)** \\ \hline Correlation Coefficient & 0.4593 & 0.0191 \\ Mean Difference & 0.3047 & 0.3855 \\ RMSE & 0.4161 & 0.4141 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Measured currents processed with the ECWMF wind field, and a comparison with GF\(-\)3 and HFSWR.