In one of the world’s most hotly contested maritime zones, satellites have picked up mysterious signals that could point to unauthorised or covert operations. The findings shed new light on a region where tensions between China and the Philippines remain dangerously high.
Eyes in the sky over a disputed sea
Nearly a decade after an international tribunal in The Hague dismissed China’s sweeping claim over most of the South China Sea, Beijing continues to defy the ruling. It has built ports, airfields, and military outposts on artificial islands – moves that have deepened friction with its neighbours, particularly the Philippines, around the Spratly Islands.
Now, satellites belonging to Unseenlabs, a French maritime intelligence company, have detected what it calls “non-cooperative behaviours” in this volatile region. Using electromagnetic intelligence (known as ELINT), the company monitors radio frequency signals emitted by vessels at sea – even those that switch off their Automatic Identification System (AIS) to avoid detection.
“Visibility in this region is often shaped by grey-zone tactics rather than transparency,” Unseenlabs noted in its latest case study. The West Philippine Sea, rich in oil, gas and fish, and crossed by crucial shipping lanes, is a natural stage for such shadowy manoeuvres.
Ships without a signal
Over two separate observation campaigns, Unseenlabs tracked the same maritime area months apart. During the first, which lasted 31 days, around 7% of detected RF transmitters had no matching AIS signal – meaning those vessels were operating “dark,” without publicly sharing their position. A follow-up 15-day mission recorded a similar figure of 6%.
By comparing these repeated observations, analysts could determine whether the anomalies were isolated events or recurring patterns. Persistent absences of AIS data, especially in such a busy corridor, point to deliberate concealment rather than random technical failures.
According to maritime security experts, these findings reinforce concerns about covert surveillance, illegal fishing or the enforcement of disputed territorial claims. ‘Grey-zone operations thrive where visibility is poor,’ one analyst explained. ‘Satellites like these are starting to turn the lights back on.’
A familiar vessel under scrutiny
Among the ships identified, one stood out – a vessel known to belong to the Chinese Coast Guard, which was patrolling near the contested Spratly Islands. During one mission, the ship’s AIS signal went silent for 45 minutes, effectively disappearing from public tracking systems.
But Unseenlabs didn’t lose sight of it. Each vessel emits a unique and stable radio signature, and by matching that signature across multiple readings, the company was able to continue following the ship’s movements throughout the blackout.
“Even when cooperative transmissions stop, our algorithms maintain tracking continuity,” Unseenlabs explained. “In this case, the ship’s regular patrols and interruptions in communication align with a broader pattern of sovereignty assertion.”
A modern cat-and-mouse game
Such behaviour is becoming increasingly common in the West Philippine Sea, where fishing boats, coastguard ships and military vessels often operate in close proximity. By briefly cutting their AIS transmitters, ships can obscure their intentions or conceal interactions – a tactic that complicates international oversight.
Satellite intelligence now offers one of the few tools capable of monitoring these opaque operations in real time. Analysts say such data could help regional governments and international bodies verify claims of maritime incursions, environmental violations or illegal resource extraction.
‘In an area as strategically important as this, transparency isn’t just about accountability – it’s about preventing conflict,’ said a spokesperson from the Asia Maritime Transparency Initiative.
Watching the shadows
As competition intensifies over the waters of the West Philippine Sea, satellite surveillance may become the region’s new frontline. For now, companies like Unseenlabs are providing a rare glimpse into the cat-and-mouse game unfolding between Beijing’s coastguard and its Southeast Asian neighbours.
While the identity of the ship in question remains classified, its behaviour tells a familiar story – one of power projection, quiet defiance, and a growing struggle for control of one of the world’s most disputed seas.
