## 4 Conclusions  
With the continuous enrichment of spaceborne SAR data in the future, the trajectory-crossing method to measure the two-dimensional current field on the sea surface will be widely used. However, at present, it is difficult to comprehensively analyze the influence of system and environmental parameters on the current measurement effect from the real SAR data. In this paper, a simulation method of two-dimensional sea-surface-current field for trajectory crossing spaceborne SAR is proposed, which can realize two-dimensional current field simulation under the given spaceborne SAR system and environmental pa  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Location Point**} & \multirow{2}{*}{**Coordinate**} & \multicolumn{2}{c}{**Simulated Data**} & \multicolumn{2}{c}{**Measured Data**} \\ \cline{3-6}  & & **Velocity** & **Direction** & **Velocity** & **Direction** \\ \hline
1 & (42.32\(-\)18.04) & 0.260 m/s & \(-9.66^{\circ}\) & 0.250 m/s & \(-16.74^{\circ}\) \\
2 & (42.32\(-\)18.12) & 0.293 m/s & \(-12.68^{\circ}\) & 0.261 m/s & \(-17.59^{\circ}\) \\
3 & (42.32\(-\)18.20) & 0.322 m/s & \(-19.78^{\circ}\) & 0.299 m/s & \(-24.05^{\circ}\) \\
4 & (42.32\(-\)18.28) & 0.312 m/s & \(-33.06^{\circ}\) & 0.275 m/s & \(-37.45^{\circ}\) \\
5 & (42.32\(-\)18.36) & 0.317 m/s & \(-42.84^{\circ}\) & 0.294 m/s & \(-47.56^{\circ}\) \\
6 & (42.24\(-\)18.36) & 0.295 m/s & \(-55.31^{\circ}\) & 0.263 m/s & \(-58.59^{\circ}\) \\
7 & (42.40\(-\)18.36) & 0.285 m/s & \(-47.69^{\circ}\) & 0.256 m/s & \(-59.21^{\circ}\) \\
8 & (42.40\(-\)18.44) & 0.297 m/s & \(-72.36^{\circ}\) & 0.268 m/s & \(-80.77^{\circ}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison between the simulated and measured current data.  
Figure 10: Statistical comparison between the simulated current field and SAR data measured current field. (**a**) Velocity and (**b**) direction.  
rameters. In the simulation process, the wave-current interaction and the influence of sea-surface backscattering on the SAR Doppler centroid frequency are considered, and the influence of the wave motion on the current measurement results is removed.  
The simulation experiment selected the real spaceborne SAR system and sea-surface environment parameters, and the results are in good agreement with the SAR data processing results, which shows the effectiveness of the simulation method in this paper. Therefore, the proposed method is conducive to the parameter analysis process of the trajectory-crossing method in the application of current measurement. However, because the influence of the wave-breaking scattering mechanism under high wind speed and sea conditions was not considered, the simulation method in this paper is not suitable for two-dimensional current field simulation in extreme marine environments. In future work, more scattering mechanisms will be considered to improve the scope of application and promote the development of application research for two-dimensional sea-surface-current field measurements.  
Conceptualization, Y.L. and J.C.; Methodology, Y.L.; Software, Y.L. and Z.L.; Validation, Y.L. and Z.L.; Formal analysis, Y.L., J.C. and Z.L.; Investigation, Y.L.; Writing--original draft preparation, Y.L.; Writing--review and editing, J.C. and Y.L.; Supervision, J.C. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.