## 5 Discussion
### Drift Prediction Analysis
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Date**} & \multicolumn{2}{c}{**Before Simplification**} & \multicolumn{2}{c}{**After Simplification**} \\ \cline{2-5}  & **Number of** & **Time Required** & **Number of** & **Time Required** \\  & **Vertices** & **Vertices** & **Time Required** \\ \hline
17 May 2021 & 34,704 & 12 m and 56 s & 218 & 1 m and 8 s \\
6 June 2021 & 58,830 & 20 m and 18 s & 391 & 1 m and 51 s \\
9 July 2021 & 101,881 & 29 m and 45 s & 602 & 2 m and 24 s \\
5 August 2021 & 35,510 & 12 m and 12 s & 225 & 1 m and 10 s \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Drift prediction times for green tide distribution envelope before and after simplification. image results on decision-making plans, this paper analyzes the monitoring results using quasi-synchronous HY-1C/D images with a resolution of 50 m and HJ-2A/B images with a resolution of 16 m (see Table 1). During the occurrence of green tide on 10 May, there were significant differences in the monitoring results of different resolution images. The 16 m resolution detected more green tide information than the 50 m resolution. This is because, during the occurrence stage, the green tide consists of small patches or thin, elongated strips along tidal channels, which the 50 m resolution images cannot detect [23]. On 6 June, during the outbreak stage of the green tide, the green tide had undergone sufficient growth, with larger patches and a wider range. The differences in the distribution area of the green tide were relatively small, with discrepancies mainly at the edge portions (see Figure 14). The figure shows two regions of difference, where it can be seen that the green tide signals in the discrepant regions are weak, and the colors are relatively light, making effective detection by the 50 m resolution HY-1 images difficult. This is because the northern green tide had undergone removal operations, with the residual green tide being relatively sparse and at the end of its growth cycle, resulting in low chlorophyll content and lighter color. Overall, there are differences in the detection results of satellite images with different resolutions. High-resolution images provide more detailed monitoring, offering more comprehensive information and forming a larger distribution range. The monitoring differences vary with the date, especially during the early stage of the green tide when monitoring smaller patches shifts the outer edge line of the distribution envelope northward. When formulating emergency decision-making plans, harvesting areas based on the higher-resolution HJ-2 monitoring results will be biased towards the north, achieving the effect of early detection and early management. Therefore, it is recommended to formulate plans based on the monitoring results of higher-resolution satellite images during the early stage. During the outbreak stage, when the green tide has undergone sufficient growth and aggregation, the differences in green tide monitoring results between different resolutions are relatively small, and the impact on emergency decision-making for the green tide is also relatively minor. Figure 14: Comparison of distribution envelopes from satellite images with different spatial resolutions: The left image shows a comparison of distribution envelopes from the HY-1 satellite with a resolution of 50 m and the HJ-2 satellite with a resolution of 16 m on 10 May, while the right image shows a comparison of distribution envelopes on 6 June.