Maritime surveillance has a fundamental limitation. It can track the vessels that choose to be tracked. A vessel that wants to go undetected can disable its transponder and become invisible to tracking systems that depend on vessels broadcasting their own position.
These are commonly called dark vessels. They are present in European waters on a continuous basis.
Why radar changes the picture
Synthetic aperture radar operates independently of what any vessel chooses to report about itself. The radar pulse bounces off the physical hull of the ship and returns to the satellite sensor regardless of whether the vessel has a transponder active. Weather, darkness, and sea conditions do not affect the detection.
Sentinel-1 provides radar coverage of European maritime zones on a revisit cycle of around six hours, in all weather conditions, day and night.
The challenge is not detection. It is correlation. A radar image of busy European waters shows many hundreds of vessel scale objects. Identifying which ones have no corresponding transponder record is an analysis task that requires matching radar positions against AIS records for the same time window.
The 72 hour exercise
Over a 72 hour period in January 2026 we processed Sentinel-1 radar imagery covering three European maritime corridors. Each radar pass was automatically correlated against the AIS record for the same time window.
The system identified eleven vessel scale radar detections with no corresponding AIS signal. Our behavioural analysis engine scored each detection against a baseline model of normal vessel movement in that corridor, examining heading, estimated speed, and position relative to known shipping lanes.
Three of the eleven detections received high anomaly scores, meaning their movement characteristics were significantly inconsistent with normal commercial traffic.
What followed
All three high anomaly detections were submitted to the relevant coastal authority within the exercise framework. All three were subsequently confirmed as subjects of ongoing maritime authority interest.
The exercise demonstrated that automated radar analysis combined with behavioural scoring can reduce the analyst workload of maritime dark vessel screening by approximately 85 percent, from reviewing hundreds of individual detections to reviewing a ranked shortlist of the highest priority cases.