When we searched for more information on the identities of these vessels we found that they were featured on a website running simulated sailing races. Since a typical range for a terrestrial antenna is at most about 60 miles, we knew something was wrong with these positions. We first noticed these false AIS tracks in groups of sailboats which appeared hundreds of miles out in the Atlantic Ocean even though shore-based AIS antennas appeared to receive their positions. Simulated sailboat races: First large-scale case of falsification This new type of simulated AIS tracks represents a significant threat to data integrity and underlines the need for vigilance when interpreting AIS data. Unlike some obviously false tracks appearing on land, these tracks appear extremely plausible - at first glance indistinguishable from real AIS positions. In these new examples, however, AIS tracks were present where vessels appear not to have been actually broadcasting AIS at all. In past cases, we observed vessels on the water that were broadcasting positions that corresponded to an area other than the true location of the vessel. Recently, we came across a new category of false AIS ship positions. In most cases, we are also able to identify the true position of the vessel. We have learned how to interpret anomalies in AIS data and, even when the ship coordinates were wrong, we never had reason to doubt that these vessels were on the water broadcasting AIS. AIS is the international system of vessel radio broadcasts used to identify vessel locations and help prevent collisions at sea. Over the years, data analysts working with Global Fishing Watch and SkyTruth noticed a number of ship tracks coming up in impossible locations-in transit over Antarctica, circling in the Utah desert and elsewhere-and we have questioned whether these false positions resulted from faulty automatic identification system (AIS) transmitters, deliberate misuse of those transmitters, or from intentional third party interference. This false information could compromise vessel safety, decrease confidence in a crucial collision avoidance system and potentially spark international conflict. Analysis of tracking data from automatic identification system broadcasts reveals vessel locations have been simulated for a number of ships, including military vessels.

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