Abstract
Collision avoidance is one of the main tasks on board ships to ensure safety at sea. To comply with this requirement, the direct ship environment, which is often modelled as the ship’s domain, has to be kept free of other vessels and objects. This paper addresses the question to which extent inaccuracies in position (P), navigation (N), and timing (T) data impact the reliability of collision avoidance. Employing a simplified model of the ship domain, the determined error bounds are used to derive requirements for ship-side PNT data provision. For this purpose, vessel traffic data obtained in the western Baltic Sea based on the automatic identification system (AIS) is analysed to extract all close encounters between ships considered as real-world traffic situations with a potential risk of collision. This study assumes that in these situations, erroneous data can lead to an incorrect assessment of the situation with regard to existing collision risks. The size of the error determines whether collisions are detected, spatially incorrectly assigned, or not detected. Therefore, the non-recognition of collision risks ultimately determines the limits of tolerable errors in the PNT data. The results indicate that under certain conditions, the probability of non-recognition of existing collision risks can reach non-negligible values, e.g., more than 1%, even though position accuracies are better than 10 m.
Highlights
The automatic identification system (AIS) data originating from vessels crossing the area of investigation were searched for situations when a pair of vessels reached their closest point of approach (CPA) at a given moment of their voyage
A critical misinterpretation of the current situation occurs when an existing collision risk cannot be detected. This case occurs if DCPA never becomes smaller than the specified diameter L of an assumed circular ship domain
Information about the exact position in relation to the planned track as well as to dangerous depth lines contributes to grounding avoidance as well
Summary
The knowledge of current position (P), navigation (N) and time (T) data of the own ship and ships operating in the same traffic area is one of the key factors for successful collision avoidance [1,2,3,4,5,6,7] This is reflected by the e-navigation strategy of the International Maritime Organization, which considers the reliable provision of PNT data onboard ships as a major challenge for the further improvement in bridge systems [8,9]. A remaining challenge is the comprehensive and homogeneous specification of the requirements for the provision of PNT data onboard ships (e.g., accuracy, integrity, continuity, availability and reliability) in the application context, i.e., with regard to the variety of nautical tasks, navigation applications, and related decision processes, considering the different traffic situations.
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