You can watch the final movements of the Stena Impero, the British-flagged tanker Iran intercepted on Friday, play out in real time. The Impero appears as a small red arrow among a bustling group of vessels passing through the Strait of Hormuz, before making a sudden u-turn and veering towards Iran’s Qeshm Island.
How was the vessel tracked so accurately? That is thanks to a technology called AIS, or Automatic Identification System. “All commercial vessels, at least, those displacing 300 DWT [deadweight tonnage] or more, continuously broadcast their position, and other details, as part of a mandated transmission,” explains Georgios Hatzimanolis, media strategist at MarineTraffic, which owns the world's largest network of coastal receiving stations and broadcasts the movements of ships.
AIS uses a very high-frequency transmission – with a range of around 72 kilometers and broadcasts every minute – to share this positional information, along with other variables like identity, speed, and course. Combined with data collected by satellite-receiving stations, this allows MarineTraffic to provide a near-real-time view of shipping activity. “We translate the information broadcast by the vessels onto the map on our platform, providing visibility on a global or local level at any given time,” Hatzimanolis explains.
On the day of the incident, which took place Friday, July 19, Marine Traffic’s online traffic spiked massively says Hatzimanolis: 1.7 million unique visitors came to the site in 24 hours; 368,595 people, checked out the vessel details page for the Stena Impero. On a normal day, a vessel would receive around 2,000. This was the highest spike the site has ever received.
So what happened in the case of the Impero? The incident occurred as the vessel was passing through the Strait of Hormuz, a passage of water just 21 miles across at its narrowest point, that connects the Persian Gulf and the Gulf of Oman. The body of water, as is the case with all narrow stretches, is governed by the 1982 United Nations Convention on the Law of the Sea (PDF). It provides the only sea passage from the Persian Gulf to the open ocean, the shipping lane is of enormous global economic and political significance.
“Roughly 20 per cent of the world’s oil passes through the Strait of Hormuz and it’s estimated that more than 75 per cent of it ends up in Asian markets,” says Christian Emery, a lecturer in International Relations at the University of Plymouth. This makes it a hotbed for disruption. “In addition, about 25 per cent of the world’s Liquid Natural Gas (LNG) transits through the Strait. Whilst the Saudis and Abu Dhabi have built pipelines to try and bypass the Strait... it remains the single most important choke point in the world’s oil transportation system.” In the 24 hours surrounding Iran's capture of the vessel, 441 distinct ships passed through the Strait, says Hatzimanolis.
Samir Madani, who runs the TankerTrackers.com, an independent online service that monitors and reports shipments and storage of crude oil, relies on MarineTraffic’s data. He explains that the Impero, which was empty of oil at the time, was sailing towards Saudi Arabia when it was approached by The Islamic Revolutionary Guard Corps (IRGC). “They tried to evade by making a U-turn onto eastbound lanes [of the strait]”, he says “And at that point, when they entered Iranian waters, they approached the Qesham islands, their AIS transponder was switched off.”
A video available online shows IRGC commandos rappelling from helicopters to seize the tanker. Madani says it is likely the boarders who turned-off the AIS transmissions.
Switching off the AIS data is typical of Iran’s vessel operators. “It's the rule rather than the exception – they switch it off when they're visiting Iran, and they switch it [AIS transpoder] off during transit,” Madani says. There are just two passages where Iranian vessels has to switch its AIS on, he explains.
One is the Suez Canal, when deliveries are made to Syria. After Iranian vessels traverse the canal, they switch it back off again, so the actual delivery to Syria cannot be tracked. The second is the busy Singapore Strait, where traffic is so high no vessel is allowed in without the AIS switched on. While AIS data acts similarly to live GPS data – flights are tracked in real time with their own receivers – the system can be abused. Non-profit Global Fishing Watch has documented ships in protected waters going dark to hide potential illegal fishing from authorities.
Disabling AIS isn't fool-proof though. Despite Iran’s actions, TankerTrackers was able to keep track of the Stena Impero via the second prong of their data collection strategy: satellite imagery. They purchase this data from Planet Labs, who own the world's largest network of satellites and photograph daily.
“They are live scanning the planet from above, helping us fill in all the gaps that we run into, in the maritime AIS data”, says Madani. “What we do is build up a database of multiple images of every vessel in order to build out a recognition system so that we can immediately identify the vessel when AIS transponders are switched off for days, weeks or months.”
This data allowed TankerTrackers to locate the Impero. “The day after we were looking for satellite imagery, and it wasn't perfectly clear, because the weather was quite hazy,” he explains. Planet Labs offered him several cleaned-up images that might have contained the Impero. “I examined this and I compared it with the past imagery, different locations, different times,” he says. “And I looked-compared it with the AIS data as well, to see what was offline what wasn't offline. And I was able to very quickly to say: ‘Yes – this is the vessel’.” These images were posted to TankerTrackers' Twitter account, showing that the Impero was located outside a navy port in Bandar Abbas.
There's no straightforward conclusion for the Impero, though. The ship's capture has intensified political tensions between the west and Iran. The Impero became involved after the seizure of the Iranian Tanker Grace 1 by the UK's Royal Marines in early July.
Both countries are now at an impasse. “The problem for the Iranians is that attacking UK shipping makes it extremely unlikely that the EU will take further risks to protect the Iranian economy from US sanctions,” Emery says. “The problem for the UK government is that it definitely doesn’t want to be dragged into supporting the Trump administration’s confrontational policy, and don’t believe a naval response will help, but it’s under pressure to protect the UK’s status as a global leader in maritime business services.”
This article was originally published by WIRED UK
