## 2 Materials and Methods
### Review of VTS Operation
Internally, the VTS is a human-machine system between the operator and the system, and the VTSO is primarily limited to the operations and maintenance of equipment related to the operation of the VTS. However, externally, mutual cooperation and communication are the primary tasks of a human-to-human system between the adjacent VTS and the target vessel. The work characteristics of the VTSO are defined as follows in the VTS task study using cognitive work analysis (CWA) [15]. * Simultaneous events: The situation changes every moment owing to the nature of shipbuilding, and the intention of the shipbuilder must be understood. Several ships may be simultaneously placed in the same situation, in different places, or under different circumstances. * Time pressure: Decisions must be made within a limited time and prompt processing of work is required. * Processing of large amounts of information: Information on the current situation in the VTS area and related historical information are required. * Accurate processing of information: An error in the information received or transmitted from a vessel is directly linked to the risk of a marine accident. * Pressure to solve a problem: There is constant psychological pressure to solve a particular situation. * Pressure to make a decision: In addition to the decision making for the vessel, other decisions such as verification and support should be made. VTS is significantly affected by geographical and environmental factors unique to the region, such as navigation density, marine accident records, port and route complexity, traffic interference, and hydrological, hydrological, and meteorological influences. These marine traffic environmental factors are the primary reasons for the establishment of the VTS, and the \"Guidelines for Vessel Traffic Services (IMO Resolution A.857 (20))\" specify the sea area where the VTS must be installed as follows [13]:  
* High traffic density
* Traffic carrying hazardous cargoes
* Conflicting and complex navigation patterns
* Difficult hydrographical, hydrological, and meteorological elements
* Shifting shoals and other local hazards
* Environmental considerations
* Interference by vessel traffic with other marine-based activities
* A record of maritime casualties
* Existing or planned vessel traffic services in adjacent waters and the need for cooperation between neighboring states if appropriate
* Narrow channels, port configuration, bridges, and similar areas where vessel progress may be restricted
* Existing or foreseeable changes in traffic patterns resulting from port or offshore terminal development or offshore exploration and exploitation in the area. CPA refers to the minimum distance between the two vessels when the own and target ships maintain the current course and speed, and gradually approach and sail. Further, TCPA refers to the time required for two vessels to reach the CPA and the minimum distance between them. VTSO utilizes CPA and TCPA as major indicators to select priorities among vessel relationship pairs in the process of vessel traffic management. CPA and TCPA can be obtained using the principle shown in Figure 1 [16; 17; 18]. If the position (longitude and latitude), course, and speed of the own ship are expressed as \(x_{o},\ y_{o},\ \theta_{o},\ v_{o}\), the position (longitude, latitude), course, and speed of the target ship are  
Figure 1: CPA and TCPA. expressed as \(x_{t},\ y_{t},\ \theta_{t},\ v_{t}\), then the CPA and TCPA of the two vessels are expressed as Equations (1)-(5).