INTERDEPENDENCIES BETWEEN EVALUATION OF COLLISION RISKS AND PERFORMANCE OF SHIPBORNE PNT DATA PROVISION

BANYŚ, Paweł; ENGLER, Evelin; HEYMANN, Frank · 2017 · Crossref

DOI: 10.20858/tp.2016.11.4.14

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Summary

This paper investigates the critical interdependency between the accuracy of shipborne Position, Navigation, and Timing (PNT) data and the reliability of collision risk evaluation. While the concept of "ship domain" defines the safety zone around a vessel that must remain clear of obstacles, existing literature often overlooks how inaccuracies in PNT data compromise the integrity of this domain. The authors aim to quantify the tolerable margins of error for PNT sensors to ensure that Decision Support Systems (DSS) can correctly identify collision risks, thereby supporting the International Maritime Organization’s strategy for resilient navigation. The study employs a two-phase methodology. First, the authors analyze Automatic Identification System (AIS) data from August 2014 in the Southern Baltic Sea, specifically the Strait of Fehmarn-Belt (open waters) and the Kiel Canal (constrained waters). They reconstructed ship domains using Fujii’s elliptical model and identified instances where vessels violated these domains, confirming that such close encounters occur frequently in maritime practice. Second, the authors developed a Monte Carlo simulation system to assess how PNT inaccuracies affect collision detection. The simulation modeled vessel encounters within a "ship arena" using circular domains, varying parameters such as Speed Over Ground (SOG), Course Over Ground (COG), and position. Gaussian error distributions were applied to simulate sensor inaccuracies, with 10^9 simulations conducted to determine the frequency of three scenarios: correct risk identification, shifted risk identification, and undetected collision risk. The results demonstrate that undetected PNT inaccuracies pose a non-negligible risk of failing to detect collisions. To maintain the probability of an undetected collision (Scenario C) below 1%, the study establishes specific accuracy thresholds: position error standard deviation must be less than 27 meters, SOG error less than 0.09 knots, and COG error less than 0.25 degrees. However, the simulations revealed that when position errors are combined with non-zero SOG and COG errors, it becomes impossible to keep the undetected collision risk below the 1% threshold. This indicates that error propagation and overlapping inaccuracies significantly degrade system performance beyond what individual sensor specifications might suggest. The significance of this work lies in its derivation of specific PNT data requirements for collision avoidance DSS. The findings challenge the adequacy of current IMO standards, which allow for larger position errors (e.g., 100 meters) suitable for open ocean navigation but insufficient for precise collision risk assessment. The paper concludes that defining PNT requirements must account for the combined effect of all error sources rather than treating them in isolation. This provides a foundational basis for developing guidelines for onboard PNT data processing units, ensuring that navigation systems provide the integrity necessary for safe ship domain management.

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