Playing Hide and Seek in the South China Sea
In this high-stakes strategic area—teeming with oil, natural gas, and fish, and crisscrossed by some of the world’s most vital shipping lanes—the battle for transparency is as murky as the seabed. As the French aerospace company Unseenlabs puts it,
“cooperative signals are often sporadic, and visibility is shaped more by grey-zone tactics than by any real transparency.”
But as it turns out, satellites now do a lot more than snap pretty pictures. For the past ten years, the Brittany-based Unseenlabs team has been working on a technology based on electromagnetic intelligence: satellites picking up radiofrequency (RF) signals emitted even by ships with their Automatic Identification Systems (AIS) switched off—either by necessity or, more often in this region, by choice.
Keeping Tabs from Space
Against the backdrop of mounting tensions in the West Philippine Sea (also known internationally as the South China Sea), Unseenlabs observed the same area of interest twice, at several months’ interval. During a 31-day campaign, 7% of identified RF emitters had no AIS signal,
“confirming the presence of vessels operating with no cooperative transmission.”
In their next 15-day campaign, that number was still a notable 6%—showing this isn’t just a fluke.
As Unseenlabs explains,
“By repeating observations over the same area at different times, our analysts can determine whether unusual signals are just oddballs or evidence of recurring patterns. This helps pinpoint where non-cooperative behavior persists—even in areas with dense maritime traffic. What remains visible through successive campaigns very likely reflects deliberate practices.”
The Curious Case of the Chinese Coast Guard
Within this context, one “vessel known to belong to the Chinese Coast Guard” operating near the fiercely contested Spratlys drew particular scrutiny. During a patrol on the first campaign, its AIS transmission mysteriously went silent for 45 minutes—but Unseenlabs never lost track.
Why? Because instead of relying on cooperative signals, Unseenlabs analysts match vessels to their unique, stable and repetitive RF signatures.
“This signature, combined with correlation methods, makes it possible to maintain continuous tracking—even when routes are erratic or cooperative transmissions stop.”
When Silence Speaks Volumes
In this specific instance,
“even though the identity of the vessel remains confidential, its behavior—including regular patrols, interruptions of its AIS transmission, and maneuvers consistent with asserting sovereignty—illustrates an emerging standard operating procedure.”
This fits right in with reports from other sources about the persistent Chinese Coast Guard presence around sensitive zones in the South China Sea.
So what are these ships hiding out there, flickering on and off the radar? Whatever it is, the satellites are still watching—and they don’t blink.
John is a curious mind who loves to write about diverse topics. Passionate about sharing his thoughts and perspectives, he enjoys sparking conversations and encouraging discovery. For him, every subject is an invitation to discuss and learn.
