So-called ‘phantom ships’ thought to be sailing in wide circles near San Francisco were actually thousands of miles away, according to expert analysis.
Bjorn Bergman, who had been examining tracking data for commercial ships, spotted the strange patterns throughout 2019.
“The fact that individual vessels in many different locations have been affected is puzzling and it’s unknown if any of these examples reflect actual disruptions of the GPS system,” he wrote in a blog post last month.
Mr Bergman noticed that nine ships were making circular movements around Point Reyes, northwest of San Francisco, at the same time.
That was according to the ships’ own GPS signals, otherwise known as automatic identification systems (AISs), which are mandated under international law to avoid collisions and monitor sea traffic.
According to Mr Bergman, who monitors shipping vessels across the world’s oceans with the environmental watchdog Global Fishing Watch, the ships were providing “fractured” signals.
He found that the vessels broadcasting circular GPS signals near the US were actually in waters near Norway, Libya, Malaysia, and Russia.
Whilst some ships were in locations where boats are known to have disrupted or scrambled GPS signals, such as the Suez Canal, other vessels were not.
Mr Bergman believes that are some possible explanations behind the strange shipping data, including GPS malfunctioning and deliberate manipulation.
There is, however, no clear answer as to what’s causing the strange phenomenon.
“It has a long history in maritime navigation,” Mr Bergman told the magazine. “There must be some connection”
“One thing that could be plausible is that it’s acting as a zero location because of the importance of this spot in developing maritime navigation systems. So if [a ship’s] reception is blocked for whatever reason they’re appearing there.”
Another reason, according to Texas university professor Todd Humphreys, is that devices were tricking the international AIS system.
He told Newsweek that the circular patterns seen in Mr Bergman’s study were similar to those seen with “off-the-shelf spoofing devices’ that are used to trick GPS systems.
“We know it’s GPS spoofing because we also see it in the data from exercise apps,” Mr Humphreys told Newsweek.
“Usually the false location is near the true one, but in other cases it’s half a world away, like Point Reyes for a ship off the coast of Africa.”