# The Ocean-Going Autonomous Ship--Challenges and Threats
## 3 Overview of the Potential Solutions to Navigational Threats  
Each problem causes a need for a development of countermeasure technologies. In the case of the collision avoidance systems for unmanned vessels, extensive research has been conducted to take the human operator out of the loop. While none of the existing unmanned vessels operated all over the world is now able to avoid collisions fully autonomously, there is a lot of interesting approaches to how this task can be solved in future. The fundamental works included the concept of ship domain. This idea is presented in [32] and has been utilized in later research, for example [33] as the basis of collision-avoidance maneuvering risk assessment, oriented to the particular ship's characteristics. There are extensive works on the automation of the collision avoidance systems to be implemented on the unmanned vessels. For example, [PERSON] et al. in [34] propose LiDAR (Light Detection and Ranging) and camera detection fusion in a real-time industrial multi-sensor collision avoidance system. They propose special beacon which can be readily detect by LiDAR, but suffers from false signals due to other reflective surfaces. An extra camera image merged with Lidar signals via a deep learning method has been proposed to solve this issue. However, such a solution can be useable on relatively short distances, for land mobile robots. A similar approach, together with the detailed description of the path-finding algorithm and the results of experiments, is presented in [35]. The authors tested their assumption using the 4-m long twin hull research platform, operating with no crew. The ideal flow theory in fluid mechanics has been incorporated into the automatic collision avoidance and route generating algorithm, as an artificial potential field for guiding marine vehicles in [36]. This is the example of a non-standard approach to the idea, how to automatically determine the optimal--outside the realm of human decisions--vessel behavior in the potential collision situation. While a lot of effort is put into the sensing of the situation in the area where the vessel is operating, to be able to apply the existing COLREGs rules, the authors of [37] and [38] propose different approach, which may by more adequate to the future autonomous vessels. The authors propose an algorithm to alter the course or speed of the vessel in advance, based on the automatic information exchange between vessels, earlier than a crossing situation even occurs. One must be aware that while some of the developments focus on the adaptation of unmanned platforms to the'man-led' traffic, others look forward to the situation where the maritime traffic might be dominated by unmanned units and traffic rules might be revised. The differences in those two ways of understanding this situation are highlighted in [39]. Automatic Identification System (AIS) system modifications can be considered, to provide the function of signaling the intentions of participants in a crossing situation, similarly to the solutions used in the aviation. Unfortunately, the conditions at sea do not allow for a simple rule that one of the participants of such a situation could maneuver left and right, and the other right and up. However, if participants could communicate their intentions to each other early in automatic mode, then communication between a manned and unmanned vessels could be sufficiently effective from the point of view of avoiding collisions. Various design aspects of the autonomous and unmanned vessels have been reviewed in [40] with the collision-avoidance aspects highlighted in the context of future development. The authors mentioned an intelligent obstacle detection and avoidance system, minimizing the risk of ships exploitation. They also presented a choice of approaches to the issue of automated path planning and guidance, applied in the modern USV prototypes.