## 4 Results
### OSU Tidal Model Data Evaluation  
Both the SSC obtained by GOCI inversion and that obtained from field measurements include periodic tidal currents and mean currents (residual currents), but the OSU tidal model can only give tidal currents. Note that tidal currents are an important part of dynamic processes in the East China Sea. Some previous studies have also shown that wind-driven velocities play a very limited role in the total SSCs in the Chinese seas, where tidal currents significantly dominate [32,41]. Therefore, we conjecture that tidal currents are the main factor driving changes in SSC during consecutive hours. Figure 10a compares continuously measured data and OSU mode data; the two have good consistency in the rotation direction. Figure 10b compares the measured current field and its corresponding OSU model current field during the active GOCI period; these are distributed at four different locations in the study area. In a few consecutive hours, the direction of each time period and the rotation direction of the OSU current vector were basically consistent with the measured current vector. In order to further verify and analyze the calculation results of OSU tidal model, the measured buoy data are selected to compare the calculated tidal currents value with the measured data. Table 2 shows the comparison between the measured results and the OSU model results. The measured average current speed is 0.39 m/s, which is close to the average current speed obtained by the OSU model of 0.38 m/s; and the average angle deviation is 43.96\({}^{\circ}\). The current speeds of the two data samples were statistically tested, and the \(p\) value was less than 0.05, indicating that the two groups of data come from different distributions, and there are significant differences between them, which is consistent with the fact that they belong to the measured data and the OSU model data, respectively. In summary, considering the measurement error, we can confirm our conjecture that in a few consecutive hours, the tidal current is the main factor driving the change in SSC. The tidal current results derived from the OSU model can be used to determine the rotation direction of the sea surface current and the direction of current in each period for several consecutive hours in the GOCI period.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \multirow{2}{*}{**Area**} & \multirow{2}{*}{**Time**} & \multicolumn{2}{c}{**Original Data**} & \multicolumn{2}{c}{**Angular Limitation Filter**} & \multicolumn{2}{c}{**Multi-Correlation Coefficient Optimization**} \\ \cline{3-8}  & & **AME** & **AAE (\({}^{\circ}\))** & **AME** & **AAE (\({}^{\circ}\))** & **AME** & **AAE (\({}^{\circ}\))** \\ \hline \multirow{3}{*}{ECS} & 10 August & 0.27 & 18.83 & 0.26 & 13.35 & 0.23 & 13.43 \\  & 11 August & 0.34 & 55.01 & 0.25 & 49.42 & 0.26 & 49.84 \\  & 13 August & 0.78 & 33.16 & 0.86 & 19.42 & 0.75 & 18.92 \\ \hline \multirow{3}{*}{SYS} & 27 June & 0.34 & 40.46 & 0.37 & 40.08 & 0.33 & 38.14 \\  & 11 July & 0.61 & 34.89 & 0.62 & 26.93 & 0.61 & 25.84 \\  & 16 July & 1.61 & 42.87 & 1.50 & 46.99 & 1.45 & 30.39 \\ \hline \multirow{3}{*}{NYS} & 5 August & 0.40 & 16.66 & 0.40 & 11.26 & 0.41 & 14.08 \\  & 6 August & 0.47 & 66.88 & 0.47 & 72.31 & 0.52 & 54.83 \\  & 7 August & 0.35 & 31.59 & 0.40 & 31.25 & 0.38 & 27.06 \\ \hline \multicolumn{3}{c}{Average} & 0.57 & 37.82 & 0.57 & 34.56 & 0.55 & 30.28 \\ \hline \end{tabular} Note: AAE: average angular error; AME: average relative magnitude error; ECS: East China Sea; SYS: southern Yellow Sea; NYS: northern Yellow Sea.  
\end{table}
Table 1: Results of different methods and original data for AAE and AME at different times.