AIS reception characterisation for AIS on/off anomaly detection

The Automatic Identification System (AIS) is a ship reporting system based on messages broadcast by vessels carrying an AIS transponder. The recent increase of terrestrial networks and satellite constellations of receivers is making AIS data one of the main sources of information for Maritime Situational Awareness activities. Nevertheless, AIS is subject to reliability and manipulation issues; indeed, the received reports can be unintentionally incorrect, jammed or deliberately spoofed. Moreover, the system can be switched off to cover illicit operations, causing the interruption of AIS reception. This paper addresses the problem of detecting whether a shortage of AIS messages represents an alerting situation or not, by exploiting the Received Signal Strength Information available at the AIS Base Stations (BS). The building of such an anomaly detector cannot overlook the characterisation of the electromagnetic propagation phenomena coming into play between ship AIS transponders and BS. This work is thus focused on the experimental investigation and characterisation of coverage patterns extracted from the real historical AIS data.