Abstract
The paper deals with a problem of automatic identification system (AIS) data analysis, especially eliminating the impact of AIS packet collision and detecting existing outliers in AIS data. To solve this problem, a clustering-based approach is proposed. AIS is a system that supports the exchange of information between vessels about their trajectories, e.g. position, speed or course. However, SAT-AIS, which enables the system to work on a global scale, struggles against packet collisions due to the fact that the satellite, which receives AIS data from ships, has a field of view that covers multiple areas that are not synchronized among themselves. As a result, the received data is difficult to process by AIS receivers, because most of the messages have a character of noise. In this paper, results of a computational experiment using k-means algorithm for packet recovery and for dealing with noise have been presented. The outcome proves that a clustering-based approach could be used as an initial step in AIS packet reconstruction, when the original data is incorrect.
Highlights
An automatic identification system (AIS) is an automatic tracking system that has been developed according to the International Maritime Organisation (IMO) regulations
This paper focuses on packet collision and recovery in the AIS system
The proposed approach is based on an unsupervised machine learning technique called clustering
Summary
An automatic identification system (AIS) is an automatic tracking system that has been developed according to the International Maritime Organisation (IMO) regulations. Due to the Earth’s curvature, the horizontal range of terrestrial AIS’ visibility is about 74 km (40 nautical miles) from shore (European Space Agency 2019) This indicates that the original AIS is a system working on a local scale, i.e. on a ship-to-ship basis or around coastal zones only. Messages sent by ships are recorded by a satellite (which has a broader range of view due to its altitude) and transmitted to ground stations for further processing and distribution (Wawrzaszek et al 2019) It seems to solve many of terrestrial AIS’ restrictions, SAT-AIS struggles against its own limitations. When multiple vessels start or stop transmitting ( assigning slots) in a communication cell, other devices may receive information from various cells (e.g. from both terrestrial AIS base station and SAT-AIS satellite), which are not organized within themselves — that is why slot (and packet) collisions appear (exactEarth 2015). The last section contains conclusions and suggestions for future research
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