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Estimating Reception Coverage Characteristics of AIS

The Automatic Identification System (AIS) is now well established and widely used in commercial shipping. The system originated from a safety mandate but AIS messages have also been shown to be useful from a security situational awareness perspective. In terms of coastal security, AIS messages are often received by land-based receivers positioned along a nation's coastline. The operational range of the receivers is controlled by complex variable VHF propagation characteristics, power of the transmitter, etc. However, certain characteristics of the reception coverage area can be determined from the AIS message receptions themselves. This paper presents an algorithm to compute coverage characteristics using AIS messages. The algorithm is applied to synthetic data with known coverage characteristics, and also real AIS data obtained from the Maritime Safety and Security Information System. Results from the Norwegian, North and Baltic Seas show how the coverage estimate is influenced by the coverage edge, lack of vessel activity, and diversity in the source data.