## 3 Case Study
### Fake Ship License Plate Judgment
#### 3.3.2 Calculation and Reasoning of Fake Ship License Plate  
For \"Xinhong 998\" multiple areas of sea track, we obtained the center point of the ship track, taking the center point as the circle, 50 nautical miles (see more in Figure 15) as the radius, and searching the ship monitoring chokepoint within the range (query to the monitoring chokepoint of Lianjiang Maritime Office). We calculated the distance between the center point of the ship track and the monitoring chokepoint, combined with the average speed of the ship's property characteristics. To obtain the approximate time difference between the ship sailing from the monitoring chokepoint and the track area (roughly 2 h and 15 min by calculation), we subtracted the time difference from the multiple track time period of \"Xinhong 998\", and obtained the time range of the monitoring chokepoint as '20 March 2021 09:45:00' to '21 March 2021 01:01:14'. We obtained the ship information of the surveillance chokepoint in this time range, identifying \"Ning Shuangshun 5568\" as the active ship under the current surveillance chokepoint in the current time range, comparing the ship information with the ship behavior characteristics graph in the current  
Figure 14: Ship multiple trajectory abnormalities. area through circular association, and combining with the fake ship license plate rules. The ship \"Ning Shuangshun 5568\" is an inland river ship, and its AIS track cannot be found, which means the ship MMSI information does not match, the ship certificate has exceeded the validity period, the ship reporting information related to this ship cannot be found, and the ship belongs to the maritime key tracking ship. Thus, it meets many characteristics of the fake ship license violation, the matching degree is high, and it can be judged that the ship has the characteristics of the fake ship license plate violation. There is a high possibility that the ship set \"Xinhong 998\" is sailing at sea, and engaging in illegal activities. This study collected questionnaire feedback from experts, and after statistical calculation, obtained the weight allocation information of ship deck rules, as shown in Table 5.  
Based on the weighted of inland river-ship-licensed seagoing ships as shown in Table 6, the following algorithm is used to determine whether the ship is a licensed ship:  
1. Check if the ship is an inland waterway ship. If so, assign a weight of 0.1 to it; otherwise, no weight will be added;
2. Check if the ship information matches. If it does not match, assign a weight of 0.4 to it; otherwise, no weight will be added;
3. Check if the ship is using certificate information or if the certificate is invalid. If so, assign a weight of 0.1 to it; otherwise, no weight will be added;
4. Check if the ship has not reported port for a long time or if the port report is inconsistent with the trajectory. If so, assign a weight of 0.2 to it; otherwise, no weight will be added;  
Figure 15: Monitoring checkpoint search. \begin{table}
\begin{tabular}{c c} \hline \hline
**Feature** & **Weight** \\ \hline Inland waterway ship & 0.2 \\ Ship information matches & 0.4 \\ Certificate is invalid & 0.1 \\ \hline Not reported port for a long time & 0.2 \\ The port report is inconsistent with the trajectory & 0.1 \\ \hline Key monitoring ship & 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Weighted features of fake ship license plates. * Check whether the ship is a key monitoring ship. If so, assign a weight of 0.1 to it; otherwise, no weight will be added. Add all weighted weight values together to obtain the total weight W of the ship;
* If W is greater than a certain threshold t (such as 0.6), it is determined that the ship is a licensed ship; otherwise, it is determined that it is not a licensed ship.