## 3 Fuzzy Set Theory-Based Risk Assessment System for Navigational Obstacles
### Collision Risk Assessment Model  
#### 3.3.1 Selection of Simulation Waters and Analysis of Ship Traffic  
The process of analyzing the vessel traffic in the target waters involved the following steps: data preprocessing, defining the grid size and data structure, analyzing the grid-space traffic patterns, and interpreting the results of the grid-space traffic pattern analysis. Data preprocessing was performed as follows: AIS data for the target waters (lat_min = 33.8, lat_max = 34.7, lon_min = 125.0, lon_max = 126.0) for the 30 day period from 1 June to 30 June 2023, were filtered by removing duplicates and outliers and excluding vessels that were stopped or anchored from the analysis. As illustrated in Figure 3, the target waters, located off the southwestern and southern coasts of South Korea, were divided into three areas for simulation purposes: (a) all waters, (b) simulation 1 waters, and (c) simulation 2 waters. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Number**} & **Risk Factor for** & **Collision Risk** & **Pollution Risk** \\  & **Navigational Obstacles** & **Assessment Factor** & **Assessment Factor** \\ \hline
1 & Size, shape, and structure & Obstacle size and quantity &
\begin{tabular}{c} Navigational obstacle \\ type and size \\ \end{tabular} \\ \hline
2 & Condition and type of damage & Not applicable & Risk of navigational obstacles \\ \hline
3 & Type and quantity of oil & Not applicable & Residual hazardous materials \\ \hline
4 &
\begin{tabular}{c} State of submersion \\ (for sunken ships) \\ \end{tabular} & Not applicable & Spill probability and risk \\ \hline
5 & Water depth and seafloor topography & Not applicable & Under-level clearance \\ \hline
6 & Tidal range, currents, and weather conditions & Current direction and force & Current \\ \hline
7 & Proximity to nearby marine facilities & Not applicable &
\begin{tabular}{c} Marine environmental sensitivity \\ (Port and navigation areas, \\ Aquaculture zones) \\ \end{tabular} \\ \hline
8 & Proximity to navigation zones and routes & \
\begin{tabular}{c} Weighting based on proximity to or \\ presence within a traffic scheme or \\ grid \\ \end{tabular} &
\begin{tabular}{c} Maritime traffic environment \\ (Port entry/exit routes, Vicinity of port boundaries, General navigation \\ routes) \\ \end{tabular} \\ \hline
9 & Ship traffic density and frequency & Number of navigating ships & Not applicable \\ \hline
10 & Ship navigation methods &
\begin{tabular}{c} Weighting based on presence of \\ specific traffic patterns \\ within a grid \\ \end{tabular} & Not applicable \\ \hline
11 & Safety of port facilities & Not applicable &
\begin{tabular}{c} Maritime traffic environment \\ (Anchorage, berthing facilities, Port entry/exit routes, Vicinity of port boundaries, Exclusion of general navigation routes) \\ \end{tabular} \\ \hline
12 & Particularly sensitive sea area (PSSA) & Not applicable &
\begin{tabular}{c} Marine environmental sensitivity \\ (Marine protected areas, Protected \\ waters, Wetlands, beaches, National \\ parks) \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Risk factors and definitions for navigational obstacles. The grid size and data structure are defined as follows. The grid structure was set up using four grid steps (approximately 2.3 \(\times\) 2.8 km) [32], as proposed by the Ministry of Oceans and Fisheries. The data structure was defined based on the Maritime Mobile Service Identity (MMSI), latitude, longitude, time, Course Over Ground (COG), and Speed Over Ground (SOG) for simulations 1 and 2 to properly allocate the data. The MMSIs of ships sailing within each grid space were then extracted, and the ship traffic was analyzed and visualized in the form of a heat map. Figure 4 shows a visualization of the areas occupied by ships in the four-level grid for each simulation.